Observed events frequencies and associated factors among soccer players during the 2021 African Cup of Nations competition: A video-based exploratory analysis

Amr Chaabeni; Amine Kalai; Helmi Ben Saad; Yacine Zerguini; Montassar Tabben; Karim Chamari; Anis Jellad

doi:10.12688/f1000research.148161.3

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Research Article

Revised

Observed events frequencies and associated factors among soccer players during the 2021 African Cup of Nations competition: A video-based exploratory analysis

[version 3; peer review: 1 approved, 2 not approved]

Previously titled: Injury incidence and associated factors among soccer players during the 2021 African Cup of Nations competition

Amr Chaabeni¹, Amine Kalai^1,2, Helmi Ben Saad³, [...] Yacine Zerguini^4,5, Montassar Tabben⁶, Karim Chamari^7,8, Anis Jellad ^1,2

Amr Chaabeni¹, Amine Kalai^1,2, [...] Helmi Ben Saad³, Yacine Zerguini^4,5, Montassar Tabben⁶, Karim Chamari^7,8, Anis Jellad ^1,2

PUBLISHED 31 Oct 2025

Author details Author details

¹ Physical Medicine and Rehabilitation, Faculty of Medicine University of Monastir, Monastir, Monastir, 5000, Tunisia
² Research Laboratory of Technology and Medical Imaging - LR12ES06, Center for Musculoskeletal Biomechanics Research, Faculty of Medicine, University of Monastir, Tunisia., Monastir, Tunisia
³ University of Sousse, Farhat Hached Hospital, Research Laboratory LR12SP09 “Heart Failure”, Sousse, Tunisia
⁴ FIFA Medical Centre of Excellence Algiers, Alger, Algeria
⁵ Medical Committee, Confederation of African Football, 6th of October City, Giza Governorate, Egypt
⁶ Aspetar, Orthopaedic and Sports Medicine Hospital, FIFA Medical Centre of Excellence, Doha, Qatar
⁷ Higher Institute of Sport and Physical Education Ksar-Said, University of La Manouba,, Tunis, Tunisia
⁸ Naufar Wellness & Recovery Center, Doha, Qatar

Amr Chaabeni
Roles: Conceptualization, Investigation, Methodology, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Amine Kalai
Roles: Methodology, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Helmi Ben Saad
Roles: Methodology, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Yacine Zerguini
Roles: Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Montassar Tabben
Roles: Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Karim Chamari
Roles: Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Anis Jellad
Roles: Conceptualization, Investigation, Methodology, Supervision, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

OPEN PEER REVIEW

REVIEWER STATUS

Abstract

Background

Understanding the epidemiology of soccer injuries during specific international competitions is essential for customizing preventive strategies. Several studies have reported outcomes related to international competitions but, to the best of our knowledge, there has been no investigation into the injury patterns during any African Cup of Nations (AFCON) tournaments. This study aimed to analyze the observed events frequencies and their characteristics during the 2021 African Cup of Nations (AFCON), which took place in Cameroon from January 9 to February 6, 2022.

Methods

A video-based analysis covering 52 matches was conducted by two independent consultant physicians. They reviewed “observed events” replays to determine frequencies and characteristics ( i.e. ; mechanisms, body location, match moment, player substitution, absence in the next match, and referee decisions).

Results

The tournament involved 519 male players, comprising 275 African (ALP) and 244 Non-African (NALP) league players. Eighty-seven “observed events” occurred, with frequencies of 1.7 and 48.8 injuries per match and per 1000 match hours, respectively. Observed event frequency rose with competition stages, particularly contact mechanism injuries. Non-contact injuries (23/87) predominantly occurred after 60 minutes of play (19/23), with the thigh being the most frequently affected body part (18/87). Older age and playing time significantly correlated with observed event occurrence (p=0.032 and p<0.001, respectively). NALP midfielders and forwards were notably injured by contact mechanisms (36/45) in the attacking zone. Although non-contact mechanisms were more common in ALP than NALP (13/42 vs. 9/45), the difference lacked statistical significance (p=0.240), with a higher rate of muscle injuries (13/42 vs. 10/45, p=0.001).

Conclusion

Muscle-related events were the most frequently observed during the 2021 AFCON, with older age and longer playing time identified as key associated factors. These events were more prevalent in ALP compared to NALP.

Keywords

Africa, Epidemiology, On-field injury, Athletes, Football, Sport

Corresponding author: Anis Jellad

Competing interests: No competing interests were disclosed.

Grant information: The author(s) declared that no grants were involved in supporting this work.

Copyright: © 2025 Chaabeni A et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

How to cite: Chaabeni A, Kalai A, Ben Saad H et al. Observed events frequencies and associated factors among soccer players during the 2021 African Cup of Nations competition: A video-based exploratory analysis [version 3; peer review: 1 approved, 2 not approved]. F1000Research 2025, 13:392 (https://doi.org/10.12688/f1000research.148161.3) First published: 25 Apr 2024, 13:392 (https://doi.org/10.12688/f1000research.148161.1) Latest published: 31 Oct 2025, 13:392 (https://doi.org/10.12688/f1000research.148161.3)

Revised Amendments from Version 2

Authors clarified that this is a video-coded event analysis, not a medical injury surveillance study. Terminology "Injury incidence" was replaced with "Observed events frequency". In the Methods section, authors specified that the reported numbers represent descriptive counts of stoppages associated with apparent discomfort rather than epidemiological injury rates. Authors Added statements acknowledging missing data (training, severity, return-to-play) and explained related feasibility constraints at AFCON tournaments.

See the authors' detailed response to the review by Afxentios Kekelekis
See the authors' detailed response to the review by Pablo Prieto González

Introduction

Soccer is a universally popular sport, boasting over 265 million licensed players globally, of which 46 million reside in Africa.¹ According to the Federation International de Football Association (FIFA), there are 128983 soccer professional players worldwide, with Africa contributing 22525, as per the Professional Football 2019 Report.² The physical demands of soccer, characterized by repetitive and high-impact movements, put players at a high risk of injuries.³ Epidemiological studies play a crucial role in sports medicine, both for enhancing athletic performance and for serving as the foundational first phase in developing and implementing effective injury prevention programs.⁴^,⁵ Importantly, injury characteristics can vary depending on geographical factors, such as climate and competition type.⁶^,⁷ For example, ACL injuries and ankle sprains are more prevalent in warmer climates, while achilles tendon injuries are more common in cooler climates.⁶ The reason why region-specific data are necessary for more effective preventive measures.

Injury rates differ significantly across competitions. For instance, the rate is 32.3 injuries per 1000 hours of exposure in national leagues, whereas it rises to 41.1 in international tournaments.⁸ Even within Africa, there is significant variability; the South African league reports 24.8 injuries per 1000 match hours,⁹ in contrast to 113.4 in the Nigerian league.¹⁰ The study of Zerguini et al.¹¹ investigating the EPFKIN league in Congo RDC revealed an alarming six injuries per game, equivalent to 182 injuries per 1000 hours of competition. Indeed, some regional competitions, such as the West Africa Football Union, exhibit even higher incidences up to 289 injuries per 1000 match hours.¹²

Despite the abundance of injury data from various leagues and tournaments worldwide, there remains a significant gap in the literature concerning injury patterns specific to the African Cup of Nations (AFCON). AFCON is a key competition in both the global and African soccer contexts. It features both local and professional players, including those from major European leagues with special infrastructure. Additionally, Africa serves as a vital talent pool for soccer players. Understanding the epidemiology of injuries within this competition is essential not only for developing localized preventive strategies but also for enhancing player safety and performance across Africa.

Thus, this study aimed to provide an exploratory, descriptive account of observed event-related stoppages during the 2021 AFCON, generating hypotheses that may inform future consensus-based surveillance research. By focusing on this previously unexplored population, this research seeks to provide novel insights into observed events trends, contributing to global sports medicine and informing future interventions tailored to African and international contexts.

Methods

Study design

This was a video-based descriptive observational study related to the 2021 AFCON, which took place in Cameroon from January 9 to February 6, 2022. The 2021 competition was postponed to 2022 because of the coronavirus disease 2019 pandemic. Twenty-four national team have participated in this competition (Box 1) with 519 players ( i.e. ; 275 African (ALP) and 244 Non-African (NALP) league players). The 52 matches were kicked off at four different times: 14:00 (n=5), 16:00 (n=1), 17:00 (n=22), and 20:00-h (n=24) (Box 2).

Box 1. Teams who participated in the African cup of nations-2022 competition (n=24).

Algeria; Burkina Faso; Cameroon; Cape Verde; Comoros; Ivory Coast; Egypt; Equatorial Guinea; Ethiopia; Gabon; Gambia; Ghana; Guinea; Guinea-Bissau; Malawi; Mali; Mauritania; Morocco; Nigeria; Senegal; Sierra Leone; South Africa; Sudan; Tunisia.

Box 2. List and times (T) of the 52 matches played during the African cup of nations-2022 competition.

Round of groups: from 9 to 20 January
Group A	Group B	Group C	Group D	Group E	Group F
Cameroon vs. Burkina Faso(T₃)	Senegal vs. Zimbabwe(T₁)	Ghana vs. Morocco(T₃)	Nigeria vs. Egypt(T₃)	Algeria vs. Sierra Leone(T₁)	Tunisia vs. Mali(T₁)
Cape Verde vs. Ethiopia(T₄)	Guinea vs. Malawi(T₃)	Comoros vs. Gabon(T₄)	Sudan vs. Guinea Bissau(T₄)	Equatorial Guinea vs. Ivory Coast(T₄)	Mauritania vs. Gambia(T₃)
Cameroon vs. Ethiopia(T₃)	Senegal vs. Guinea(T₁)	Morocco vs. Comoros(T₃)	Nigeria vs. Sudan(T₃)	Ivory Coast vs. Sierra Leone(T₃)	Gambia vs. Mali(T₁)
Cape Verde vs. Burkina Faso(T₄)	Malawi vs. Zimbabwe(T₃)	Gabon vs. Ghana(T₄)	Guinea Bissau vs. Egypt(T₄)	Algeria vs. Equatorial Guinea(T₄)	Tunisia vs. Mauritania(T₃)
Burkina Faso vs. Ethiopia(T₃)	Zimbabwe vs. Guinea(T₃)	Ghana vs. Comoros(T₄)	Egypt vs. Sudan(T₄)	Sierra Leone vs. Equatorial Guinea(T₃)	Mali vs. Mauritania(T₄)
Cape Verde vs. Cameroon(T₃)	Malawi vs. Senegal(T₃)	Gabon vs. Morocco(T₄)	Guinea Bissau vs. Nigeria(T₄)	Ivory Coast vs. Algeria(T₃)	Tunisia vs. Gambia(T₄)
Round of 16: from 23 to 26 January
Burkina Faso vs. Gabon(T₃)^*
Nigeria vs. Tunisia(T₄)
Guinea vs. Gambia(T₃)
Cameroon vs. Comoros(T₄)
Senegal vs. Cape Verde(T₃)
Morocco vs. Malawi(T₄)
Ivory Coast vs. Egypt(T₃)^*
Mali vs. Equatorial Guinea(T₄)^*
Quarter-final: from 29 to January 30
Gambia vs. Cameroon(T₃)
Burkina Faso vs. Tunisia(T₄)
Egypt vs. Morocco(T₂)^*
Senegal vs. Equatorial Guinea(T₄)
Semi-final: February 2 and 3
Burkina Faso vs. Senegal(T₄)
Cameroon vs. Egypt(T₄)^*
Match for 3^rd place: February 5
Burkina Faso vs. Cameroon(T₄)
Final: February 6
Senegal vs. Egypt(T₄)^*

* Match with extra-time

There was no need for an ethical committee approval as the data were taken from publicly available video footages. The study was conducted following the guidelines established by the STROBE statement.¹³

Study protocol

Two independent consultant physicians, ( AJ and AC in the authors’ list, with 17 and 4 years’ experience in sports medicine and physical rehabilitation, respectively), followed the live streaming of matches (Box 2) and collected data and observed-events related to every match. Potential biases, such as selection bias in event reporting, were mitigated by comprehensive video replay review, capturing all visible match incidents. In case of discrepancy, the intervention of a third author (AK) was required. Given that our approach relied on video-coded interruptions rather than medical injury surveillance, incidents measures should be interpreted as observed events frequencies rather than true epidemiological incidence rates.

An event was defined as any observed incident causing a match interruption of more than 15 seconds, during which a player appeared to be in pain or received medical attention, regardless of whether it resulted in absence from the match or training, consistent with previous studies.¹⁴^–¹⁶ It is important to note that this approach represents a video-coded event analysis rather than a medical injury surveillance system, and therefore does not adhere strictly to international consensus injury definitions ( e.g. ; International Olympic Committee, Union of European Football Associations, FIFA). Events identified may reflect transient discomfort, tactical behavior, or precautionary stoppages, and should not be interpreted as confirmed medical diagnoses.

Observed events responding to the previous definition were included in the study. Events occurring during training or warm-up were excluded.

Each observed event was characterized according to the characteristics of the:

i) Player’s age, playing position (goalkeeper, defender, midfielder, and forward), the league where the footballer was playing in at the moment of the competition ( i.e. ; NALP or ALP);
ii) Incident: Mechanism (contact vs. non-contact), body location (upper extremity, head and neck, trunk, thigh, knee, ankle), moment during the match, replacement after injury, absence next match, and eventual referee’s sanction;
iii) Match: Time, temperature and humidity (displayed at the presentation of each match just before the kick-off ), and competition stage ( e.g. ; round of groups, round of 16, quarterfinals, semi-finals, and finals (the third-place and final matches)).

Observed event with contact mechanism was defined with any “physical contact with other player or object”,¹⁴^,¹⁷ otherwise it was considered as non-contact mechanism. Body location was classified by anatomical regions based on previous studies.⁸^,¹⁸

The moment of the observed event was categorized into six “15-min” periods of standard match¹⁹^,²⁰ ( i.e. ; 0-15, 16-30, 31-45, 46-60, 61-75, and 76-90 minutes), as the added extra-time was considered as a seventh period ( i.e. ; > 90 min).

Statistical analysis

The Kolmogorov–Smirnov test was used to analyze the distribution of quantitative data. All quantitative data (except for time played) were normally distributed, and therefore were presented as means ± standard-deviation, and time played was expressed as median (interquartile). Mean difference (95% confidence interval) between two groups was calculated for the quantitative data. Categorical data were expressed as frequencies. For the analytical study, the Student’s t-test was used to compare means for normally distributed variables, while the Mann-Whitney U test was employed to compare medians for non-normally distributed variables. The 2-sided Chi squared test was used to compare the categorical data and rates between groups.

Following previous studies, we calculated the number of observed events per match and per 1000 match hours.¹⁵^–¹⁷ We have calculated the total hours of ‘match play’ as follows: 22 players × match duration using the factor 1.5, based on standard 90 min match play.¹⁵^,¹⁶ We decided to consider the 30 minutes possible extra-time during play offs ( i.e. ; rounds of 16, quarterfinal, semi-finals, and finals), we added the factor 0.5 for the matches requiring extra-time. Therefore, in this case we used the formula as follows: 22 players × match duration using factor 2.

The collected data were analyzed using a statistical software (StatSoft, Inc. (2014). STATISTICA (data analysis software system), version 12. www.statsoft.com, RRID: SCR_014213). The significance level was set at p<0.05.

Results

During the 2021 AFCON competition, 52 matches were played, among which seven required the addition of extra-time (Box 2). The total number of players who effectively participated in the AFCON was 519 (244 (47%) were NALP) ( Table 1). All NALP were European league players.

Table 1. African cup of nations (2022 competition): General characteristics.

Variable	Category	Value
Participating teams		24
Convoked players		672
Effectively participating players		519
Players’ league	Non-African	244 (47.0)
Players’ league	African	275 (53.0)
Age of effectively participating players (Year)		26±3
Age of “non-African” league players (Year)		25±3
Age of African league players (Year)		26±3
Players’ positions (“non-African” league/African league)	Goalkeeper	41 (7/34)
	Defender	153 (76/77)
	Midfielder	177 (89/88)
	Forward	148 (72/76)
Total number of matches		52
Number of matches with extra time		7
Temperature (°C)		28±2
Humidity (%)		55±15
Time of match	14:00	5 (9.6)
	16:00	1 (1.9)
	17:00	22 (42.3)
	20:00	24 (46.1)

During the competition, 87 events were recorded, with 45 (51.7%) in NALP and 42 (48.2%) in ALP. These events occurred in 77 players, with 34 (44%) NALP and 43 (56%) ALP. The overall observed event frequencies were 1.7 and 48.8 events per match and per 1000 match hours, respectively. These values represent stoppages associated with apparent discomfort, not medically confirmed injury rates. The average age of players with events was 26±4 years. The observed event mechanisms were contact in 64 (74%) and non-contact in 23 (26%) cases. When analyzed by match time, 9 (10%) events occurred at 14:00, 43 (49%) at 16:00 and 17:00, and 35 (40.2%) at 20:00. Observed events frequencies also varied by the round of the competition. A higher rate of events was recorded in playoff (2.5±1.5) compared to groups’ stage (1.3±1.2) (p=0.002).

Events resulting from contact mechanisms were mainly observed during the 16-30- and 76-90-minute intervals of the game (17/65 (26%) and 14/65 (21.5%) of observed events, respectively) ( Figure 1). Most non-contact events were observed after 60 minutes of play (19/23; 82.6%) ( Figure 1). The percentage of observed events due to contact mechanism compared to non-contact mechanism was significantly higher during the intervals of 0-15, 16-31 minutes, and 46-60 minutes ( Figure 1). Lower extremity events accounted for 65.5% of the total observed events (57/87). The most common observed events locations were the thigh (20.7%), ankle (17.2%), and knee (16%).

Figure 1. Distribution of observed events by mechanism and time intervals of the match.

^#p-value (2-sided Chi squared test test) < 0.05: Comparison between the 2 groups.

The frequency of observed events per match increased with the competition stage, especially those caused by contact mechanism ( Figure 2). The highest frequency was noticed during the finals ( Figure 2).

Figure 2. Progression of observed events by match rounds.

Table 2 displays the factors associated with observed events. Compared to the group of players free from events, the group of players with events was significantly older, had played longer than the players free from events, and included a higher percentage of goalkeepers.

Table 2. African cup of nations (2022 competition): Factors associated with observed events.

Factors	category	Players with events(n=77)	Players free from events(n=442)	p-value
Age (Year)		27±4	26±3	0.032^*
Player position	Goalkeeper	13 (17)	28 (6)	0.002^#
	Defender	21 (27)	132 (30)	0.644^#
	Midfielder	23 (30)	154 (35)	0.402^#
	Forward	20 (26)	128 (30)	0.591^#
Players’ league	«Non-African»	34 (44)	210 (48)	0.586^#
Players’ league	African	43 (56)	232 (52)	0.586^#
Time played	Minutes	262 [171-425]	160 [73-270]	0.001^*
Temperature (°C)		28.8±2.4	28.5±2.7	0.309*
Humidity (%)		52.4±12.3	51.0±15.8	0.476*

* p-value (Student t test or Mann-Witney U test) < 0.05: Comparison of quantitative data between the 2 groups.

# p-value (2-sided Chi squared test test) < 0.05: Comparison of categorical data between the 2 groups.

Table 3 displays the comparison between NALP and ALP in terms of observed events characteristics. The NALP with events were significantly younger than the ALP. Non-contact mechanisms and muscle observed events were more common in the ALP compared to the NALP. In the NALP group, observed events were more frequent for midfielders and forwards than goalkeepers and defenders.

Table 3. Comparison between «non-African» league players (NALP) and African league (ALP) players in terms of observed events characteristics.

Data	Category	NALP (n=45)	ALP (n=42)	p-value
Age (Year)		25.9±4.0	27.9±3.6	0.017^*
Age of players with muscle observed events (Year)		25±3.3	28.4±3.8	0.038^*
Player position	Goalkeeper and defender	18 (40)	25 (60)	0.069
Player position	Midfielder and forward	27 (60)	17 (40)	0.069
Mechanisms of the observed events	Non-contact	9 (20)	13 (31)	0.240
Mechanisms of the observed events	Contact	36 (80)	29 (69)	0.240
Type of observed events	Muscle	10 (22.2)	13 (31)	0.001^*
Type of observed events	Other	35 (77.8)	29 (69)	0.001^*
Replacement of the player	Yes	15 (33.3)	23 (54.8)	0.044^*
Absence next match	Yes	6 (13.3)	15 (35.7)	0.015^*
Temperature (°C)		28.8±4.6	27.9±3.7	0.339
Humidity (%)		58.1±10.2	53.5±12.0	0.317

* p-value (Student t test or 2-sided Chi squared test) < 0.05: comparison between the 2 groups.

Discussion

The present study identified observed events’ frequencies of 48.8 per 1000 match hours and 1.7 per match during the 2021 AFCON. These figures represent descriptive match events rather than epidemiological injury frequencies, and therefore complement rather than replace consensus-based surveillance data. The rate of observed events per match increased with the competition stage. Observed events occurred mostly in goalkeepers. Non-contact events occurred mainly during the last third of the game. Observed events involved mainly lower extremity with the thigh being the most common concerned location. Players with events were significantly older and had longer amount of time played compared to those free from events. NALP were “injured” mainly by contact mechanism, in the attacking zone of the field and events involved especially midfielders and forwards. Non-contact mechanism was more common in ALP with a higher rate of muscle events compared to NALP.

The documented frequency of observed events per 1000 match hours in the present study ( i.e. ; 48.8) is comparable to the 50.8 injury incidence reported during the 2014 FIFA World Cup,¹⁷ but is higher than incidences reported by Waldén et al.²¹ during the 2004 European Football Championship (EURO) (36 per 1000 match hours) and by Bengtsson et al.²² during the 2015/2016 and 2016/2017 Champions League seasons (20.3 per 1000 match hours) and 2016 Copa Libertadores (20.9 per 1000 match hours). The documented observed events frequency is lower than the injuries incidences reported during the FIFA World Cup hold in Korea/Japan 2002, Germany 2006, and South Africa 2010, respectively 81, 68.7, and 61.1 per 1000 match hours.¹⁵^,¹⁶^,²³ Moreover, the frequency of observed events per match we reported ( i.e. ; 1.7 observed events) is comparable to the 1.68 reported incidence of injuries during the 2014 FIFA World Cup¹⁷ but (i) Lower than injuries incidences noticed during FIFA World Cup (2.3 per match), Olympic Games (2.3 per match) and FIFA confederation cups (2.8 per match) from 1998 to 2012²⁴; and (ii) Higher than injuries incidences noticed during the 2017 Gold Cup¹⁴ and EURO 2004,²¹ 1.22 and 1.04 per match respectively. This discrepancy may potentially be due to the different type of competition/environment, the improvement in “injuries/events” prevention programs and the strict referees’ interventions. Indeed, the decrease in the injuries’ incidence in recent years was noticed by Junge et Dvořák¹⁷ and explained by the referee sanctions’ evolution and the greater fair play by players. Differences in injury/events definitions and data collection methods across studies may account for variations in injury/events rates, highlighting the need for standardized reporting.

The increase of the rate of observed events with competition stages in our study is aligned with the conclusions of Yoon et al.²⁵ This can be explained by the cumulative fatigue during playoffs and the fact that physical commitment on the field is increasingly important as players approach the finals. Observed events during the later stages of the tournament may have influenced player availability and team outcomes, with key players missing subsequent matches. Discordantly, Junge et al.¹⁵ reported no significant association between the incidence of injuries and the competition stages. The latter study investigated the 2002 FIFA World Cup, which included a higher number of matches and a different organization than continental competitions.

In accordance with our findings, the literature reported that, the incidence of injury within a match time increases especially after 60-min of the game.¹⁴^,²⁶ As players spent more time on the field, the incidence of muscle injuries increased significantly. This is comparable to the results of Pangrazio and Forriol²⁶ and Chahla et al.¹⁴ In fact, Pangrazio and Forriol²⁶ reported during the 2015 America cup that muscle strains happened in the last quarter of the match. Chahla et al.¹⁴ reported an increase of injuries’ incidence with play time, especially between the 60^th and 75^th minute of play. Physical fatigue is the main explanatory factor according to some authors.¹⁴^,²⁷ Other studies have reported the increase of injuries during the end of each half¹⁵^,¹⁹^,²⁰^,²⁸ with the high intensity of the match as possible explanation.¹⁵ Non-contact observed events were most prevalent among midfielders and forwards, particularly during the last third of the match, likely due to accumulated fatigue. In contrasts with our results, Dvořák et al.²³ identified no differences in injuries’ distribution between the two halves.

Studies about soccer injuries identified that lower extremity is by far the most affected body part. Similarly to our findings, the thigh has previously been reported as the most commonly injured body part.⁸^,¹⁷^,¹⁹^,²⁶^,²⁹ Soccer injuries epidemiology studies identified the older age as one of the main risk factors for muscle injuries.²⁰^,³⁰^–³² In concordance with Pangrazio and Forriol²⁶ and Arnason et al.,³⁰ we found that players who played for longer times were more exposed to events. Thus, the longer the exposure was (related to the long-time of practice), the higher the rate of observed events/injuries was.²⁶

There is no agreement in the literature about the rate of injuries/events by player position. We found that goalkeepers had the highest rate of observed events. Chahla et al.¹⁴ and Arliani et al.³³ reported that forward players had the highest rate of injuries, while Chomiac et al.³⁴ reported the defenders as the most injured. This divergence in findings between studies may be explained by the difference of competitions type with the playing style potentially exposing specific player’s positions to a higher risk of being injured, and by differences in injury/events definitions.

No previous study has investigated the injuries/events characteristics between players belonging to different continental leagues at the same competition. The higher rate of contact events noticed in our study among NALP may be explained by the fact that these players are essentially forward and midfielder players with high level of skills, commonly “injured” in the attacking zone of the field. The fact that ALP in our study had the highest rate of muscle events may be explained by the difference in training cultures between continents as it was reported between South American and Asian competitions and European competition.²²^,²⁵ While our study identified significant differences in observed events between ALP and NALP, the underlying reasons for these variations were not fully explored. It is possible that geographical and cultural differences in training practices, such as variations in training intensity, recovery protocols, and match frequency, may contribute to these differences. Future research should focus on examining how these regional and cultural factors impact injury mechanisms and outcomes, as they likely play a role in the observed discrepancies between ALP and NALP.

Study limitations

A key limitation is that our event coding did not follow consensus definitions of sports injury surveillance. Instead, we relied on video-based observations of match interruptions, which may overestimate or underestimate medically confirmed injuries. We therefore interpret these findings as descriptive indicators of match events rather than validated epidemiological injury data. The video-based analysis approach used in our study did not include training and potential match’ warm-up-related injuries. Furthermore, our design did not allow for collection of observed event severity, medical confirmation, or return-to-play outcomes. As a result, the burden and recovery impact of the observed events remain unknown, which limits comparability with consensus-based epidemiological studies. These omissions are related to feasibility constraints inherent to AFCON tournaments, where centralized medical surveillance data are not accessible. This exclusion may underestimate the total injury burden, as training injuries/events are known to contribute significantly to overall injury/events rates. Furthermore, due to the study design, observed events severity and recovery duration are not reported, missing an important piece of information of the recent epidemiological studies, i.e. injury/event burden.²⁹^,³⁵ Future studies should incorporate this information to better understand the long-term effects on player performance. Accordingly, our findings should be interpreted as exploratory, offering complementary descriptive insights into AFCON match events rather than definitive epidemiological estimates. Additionally, future research should address the limitations of this study by including training injuries/events, analyzing the impact of injury/event prevention measures, and evaluating the role of conditioning programs to determine their effectiveness in reducing injury/events rates, thereby providing a more comprehensive understanding of injury/events epidemiology.

Conclusion

We report an observed events frequency of 48.8 per 1000 match hours and a frequency of 1.7 observed events per match during the 2021 AFCON. Older age and longer playing time were the main factors associated with observed events. NALPs were mostly ‘injured’ by contact mechanisms, while ALPs were mainly “injured” by non-contact mechanisms. ALPs had the highest rate of muscle observed events. These findings may highlight the importance of preventive interventions, especially targeting muscle incidents in ALPs.

Ethics and consent

Ethical approval and written consent were not required.

Data availability statement

Underlying data

Zenodo: Excel data of the study titled: Observed events frequencies and associated factors among soccer players during the 2021 African Cup of Nations competition: A video-based exploratory analysis. DOI: https://doi.org/10.5281/zenodo.10465671.³⁶

The project contains the following underlying data:

- Excel Data with description of observed events, matches and players’ characteristics.

Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).

Reporting guidelines

Zenodo: STROBE of the paper titled: Observed events frequencies and associated factors among soccer players during the 2021 African Cup of Nations competition: A video-based exploratory analysis. DOI: https://doi.org/10.5281/zenodo.10944493.³⁷

Acknowledgments

In memory of Yacine ZERGUINI, a dedicated contributor to this article whose passion for sports science and commitment to advancing our understanding of athlete health and performance was truly inspiring. Yacine’s invaluable insights and contributions to the research on injury incidence among soccer players during the 2021 African Cup of Nations competition will forever remain a testament to his expertise and dedication to the field. However, he is no longer with us, his impact on this work and on the broader sports science community will continue to be felt. The authors disclose that two artificial intelligence tools—ChatGPT (ephemeral version) and QuillBot—were utilized to improve the clarity and coherence of the manuscript. These tools were used exclusively for language refinement, without modifying the scientific content or generating original material.³⁸ The authors would like to express their sincere gratitude to the reviewers for their excellent feedback, which has substantially improved the quality of this work. Their insightful comments and constructive suggestions were invaluable in refining our manuscript.³⁹

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15. Junge A, Dvorak J, Graf-Baumann T: Football injuries during the World Cup 2002. Am. J. Sports Med. 2004 Jan-Feb; 32(1 Suppl): 23S–27S. PubMed Abstract
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Comments on this article Comments (0)

Version 3

VERSION 3 PUBLISHED 25 Apr 2024

Author details Author details

Amr Chaabeni
Roles: Conceptualization, Investigation, Methodology, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Amine Kalai
Roles: Methodology, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Helmi Ben Saad
Roles: Methodology, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Yacine Zerguini
Roles: Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Montassar Tabben
Roles: Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Karim Chamari
Roles: Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Anis Jellad
Roles: Conceptualization, Investigation, Methodology, Supervision, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Competing interests

No competing interests were disclosed.

Grant information

The author(s) declared that no grants were involved in supporting this work.

Article Versions (3)

version 3

Revised

Published: 31 Oct 2025, 13:392

https://doi.org/10.12688/f1000research.148161.3

version 2

Revised

Published: 13 Jan 2025, 13:392

https://doi.org/10.12688/f1000research.148161.2

version 1

Published: 25 Apr 2024, 13:392

https://doi.org/10.12688/f1000research.148161.1

© 2025 Chaabeni A et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Chaabeni A, Kalai A, Ben Saad H et al. Observed events frequencies and associated factors among soccer players during the 2021 African Cup of Nations competition: A video-based exploratory analysis [version 3; peer review: 1 approved, 2 not approved]. F1000Research 2025, 13:392 (https://doi.org/10.12688/f1000research.148161.3)

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ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested

Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.

Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions

Version 2

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PUBLISHED 13 Jan 2025

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Reviewer Report 11 Sep 2025

Afxentios Kekelekis, Aristotle University of Thessaloniki, Serres, Greece

Not Approved

https://doi.org/10.5256/f1000research.176730.r409125

The manuscript entitled “Injury incidence and associated factors among soccer players during the 2021 African Cup of Nations competition” addresses an important competition and a population that has not been widely studied in the epidemiological literature. However, there are major methodological concerns that severely limit the validity of the findings.The principal issue lies in the exclusive reliance on video-based analysis to define and record injuries. The authors report that an injury was defined as any interruption in play lasting more than 15 seconds where a player appeared to be in pain or received medical attention. This definition does not align with internationally accepted consensus statements (IOC, FIFA, UEFA), which require medical confirmation and/or time-loss criteria. Because of this, it is impossible to determine whether the incidents recorded represented true musculoskeletal injuries, transient complaints such as cramps or knocks, or tactical simulations aimed at gaining advantage. Consequently, the calculated incidence rates (48.8 injuries/1000 match hours; 1.7 injuries/match) cannot be interpreted as true epidemiological measures but rather as counts of all stoppages associated with apparent discomfortFurthermore, no data were collected on training injuries, warm-up incidents, injury severity, diagnostic confirmation, or return-to-play duration.

This omission substantially underestimates the overall burden of injury and prevents meaningful comparisons with existing epidemiological surveillance systems. The reliance on observational coding without validation or medical oversight introduces a high risk of misclassification and selection bias. Without these essential elements, the study should not be considered an epidemiological investigation, but rather a descriptive video analysis of match events. In its current form, the paper cannot provide robust conclusions about injury incidence, mechanisms, or risk factors. While the intention to describe injuries at AFCON is commendable, the methodological flaws undermine both internal validity and external generalisability. I would encourage the authors to explicitly acknowledge these limitations, refrain from presenting the results as epidemiological incidence rates, and instead frame the work as exploratory video-based observations. Only with medically confirmed data, standardised definitions, and comprehensive surveillance (including training and severity outcomes) can a study of this type contribute reliable information to the injury epidemiology literature.

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

No
Are sufficient details of methods and analysis provided to allow replication by others?

No
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

No
Are the conclusions drawn adequately supported by the results?

No

References

1. Fuller C, Ekstrand J, Junge A, Andersen T, et al.: Consensus statement on injury definitions and data collection procedures in studies of football (soccer) injuries. Scandinavian Journal of Medicine & Science in Sports. 2006; 16 (2): 83-92 Publisher Full Text

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Injury epidemiology, Injury risk analysis

I confirm that I have read this submission and believe that I have an appropriate level of expertise to state that I do not consider it to be of an acceptable scientific standard, for reasons outlined above.

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Author Response 31 Oct 2025

Anis Jellad, Physical Medicine and Rehabilitation, Faculty of Medicine University of Monastir, Monastir, 5000, Tunisia

31 Oct 2025

Author Response

Dear Reviewer,
We sincerely thank you for your careful reading of our manuscript and for the constructive critiques, you have provided.
Your observations have been invaluable in helping us clarify ... Continue reading Dear Reviewer,
We sincerely thank you for your careful reading of our manuscript and for the constructive critiques, you have provided.
Your observations have been invaluable in helping us clarify the scope, strengthen the methodology section, and better situate our findings within the literature.
Below we provide a detailed, point-by-point response to the concerns raised.

1. Concern: Use of video analysis and non-consensus injury definition
Response: We agree with the reviewer that our injury definition does not follow the IOC/FIFA/UEFA consensus statements. To address this, we have clarified in the Methods section that our study is a video-coded event analysis rather than a medical injury surveillance study. We explicitly acknowledge in the Discussion section, that the coded events may include transient discomfort or tactical behavior and should not be interpreted as medically confirmed injuries. References to the consensus statements have been added to situate our approach within existing standards.
2. Concern: Reported “incidence rates” are not true epidemiological measures
Response: We appreciate this important point. To avoid misinterpretation, we have replaced the term “incidence rates” with “observed event frequencies” throughout the manuscript.
In the Title, we changed “Injury incidence” by “observed event frequencies”.
In the Methods section, we now specify that the reported numbers represent descriptive counts of stoppages associated with apparent discomfort rather than epidemiological injury rates.
In the Results and Discussion sections, we emphasize that these values should be interpreted as descriptive indicators rather than epidemiological measures.

3. Concern: Absence of training data, warm-up incidents, injury severity, severity, diagnostic confirmation, and return-to-play outcomes
Response: We recognize the absence of training surveillance, injury severity grading, and return-to-play outcomes as important limitations. We have added explicit statements in the Methods and Discussion sections, noting that such data were not available within the scope of this study. In the Limitations subsection, we explaine that this precludes direct comparison with consensus-based epidemiological studies and that these omissions reflect feasibility constraints inherent to AFCON tournaments, where access to centralized medical surveillance data is limited.

4. Concern: Framing of the study as epidemiology
Response: We agree that our initial framing overstated the scope of the work. The manuscript has been revised to present the study as exploratory and hypothesis-generating. The title, abstract, and introduction section have been reframed to emphasize that our work provides descriptive insights into match events at AFCON, complementing rather than replacing consensus-based injury surveillance systems. The Discussion section explicitly acknowledges this positioning, clarifying that our findings are descriptive indicators and should not be considered definitive epidemiological estimates.
Dear Reviewer,
We sincerely thank you for your careful reading of our manuscript and for the constructive critiques, you have provided.
Your observations have been invaluable in helping us clarify the scope, strengthen the methodology section, and better situate our findings within the literature.
Below we provide a detailed, point-by-point response to the concerns raised.

1. Concern: Use of video analysis and non-consensus injury definition
Response: We agree with the reviewer that our injury definition does not follow the IOC/FIFA/UEFA consensus statements. To address this, we have clarified in the Methods section that our study is a video-coded event analysis rather than a medical injury surveillance study. We explicitly acknowledge in the Discussion section, that the coded events may include transient discomfort or tactical behavior and should not be interpreted as medically confirmed injuries. References to the consensus statements have been added to situate our approach within existing standards.
2. Concern: Reported “incidence rates” are not true epidemiological measures
Response: We appreciate this important point. To avoid misinterpretation, we have replaced the term “incidence rates” with “observed event frequencies” throughout the manuscript.
In the Title, we changed “Injury incidence” by “observed event frequencies”.
In the Methods section, we now specify that the reported numbers represent descriptive counts of stoppages associated with apparent discomfort rather than epidemiological injury rates.
In the Results and Discussion sections, we emphasize that these values should be interpreted as descriptive indicators rather than epidemiological measures.

3. Concern: Absence of training data, warm-up incidents, injury severity, severity, diagnostic confirmation, and return-to-play outcomes
Response: We recognize the absence of training surveillance, injury severity grading, and return-to-play outcomes as important limitations. We have added explicit statements in the Methods and Discussion sections, noting that such data were not available within the scope of this study. In the Limitations subsection, we explaine that this precludes direct comparison with consensus-based epidemiological studies and that these omissions reflect feasibility constraints inherent to AFCON tournaments, where access to centralized medical surveillance data is limited.

4. Concern: Framing of the study as epidemiology
Response: We agree that our initial framing overstated the scope of the work. The manuscript has been revised to present the study as exploratory and hypothesis-generating. The title, abstract, and introduction section have been reframed to emphasize that our work provides descriptive insights into match events at AFCON, complementing rather than replacing consensus-based injury surveillance systems. The Discussion section explicitly acknowledges this positioning, clarifying that our findings are descriptive indicators and should not be considered definitive epidemiological estimates.
Competing Interests: No competing interests were disclosed. Close
Report a concern
Respond or Comment

COMMENTS ON THIS REPORT

Author Response 31 Oct 2025

Anis Jellad, Physical Medicine and Rehabilitation, Faculty of Medicine University of Monastir, Monastir, 5000, Tunisia

31 Oct 2025

Author Response

Dear Reviewer,
We sincerely thank you for your careful reading of our manuscript and for the constructive critiques, you have provided.
Your observations have been invaluable in helping us clarify ... Continue reading Dear Reviewer,
We sincerely thank you for your careful reading of our manuscript and for the constructive critiques, you have provided.
Your observations have been invaluable in helping us clarify the scope, strengthen the methodology section, and better situate our findings within the literature.
Below we provide a detailed, point-by-point response to the concerns raised.

1. Concern: Use of video analysis and non-consensus injury definition
Response: We agree with the reviewer that our injury definition does not follow the IOC/FIFA/UEFA consensus statements. To address this, we have clarified in the Methods section that our study is a video-coded event analysis rather than a medical injury surveillance study. We explicitly acknowledge in the Discussion section, that the coded events may include transient discomfort or tactical behavior and should not be interpreted as medically confirmed injuries. References to the consensus statements have been added to situate our approach within existing standards.
2. Concern: Reported “incidence rates” are not true epidemiological measures
Response: We appreciate this important point. To avoid misinterpretation, we have replaced the term “incidence rates” with “observed event frequencies” throughout the manuscript.
In the Title, we changed “Injury incidence” by “observed event frequencies”.
In the Methods section, we now specify that the reported numbers represent descriptive counts of stoppages associated with apparent discomfort rather than epidemiological injury rates.
In the Results and Discussion sections, we emphasize that these values should be interpreted as descriptive indicators rather than epidemiological measures.

3. Concern: Absence of training data, warm-up incidents, injury severity, severity, diagnostic confirmation, and return-to-play outcomes
Response: We recognize the absence of training surveillance, injury severity grading, and return-to-play outcomes as important limitations. We have added explicit statements in the Methods and Discussion sections, noting that such data were not available within the scope of this study. In the Limitations subsection, we explaine that this precludes direct comparison with consensus-based epidemiological studies and that these omissions reflect feasibility constraints inherent to AFCON tournaments, where access to centralized medical surveillance data is limited.

4. Concern: Framing of the study as epidemiology
Response: We agree that our initial framing overstated the scope of the work. The manuscript has been revised to present the study as exploratory and hypothesis-generating. The title, abstract, and introduction section have been reframed to emphasize that our work provides descriptive insights into match events at AFCON, complementing rather than replacing consensus-based injury surveillance systems. The Discussion section explicitly acknowledges this positioning, clarifying that our findings are descriptive indicators and should not be considered definitive epidemiological estimates.
Dear Reviewer,
We sincerely thank you for your careful reading of our manuscript and for the constructive critiques, you have provided.
Your observations have been invaluable in helping us clarify the scope, strengthen the methodology section, and better situate our findings within the literature.
Below we provide a detailed, point-by-point response to the concerns raised.

1. Concern: Use of video analysis and non-consensus injury definition
Response: We agree with the reviewer that our injury definition does not follow the IOC/FIFA/UEFA consensus statements. To address this, we have clarified in the Methods section that our study is a video-coded event analysis rather than a medical injury surveillance study. We explicitly acknowledge in the Discussion section, that the coded events may include transient discomfort or tactical behavior and should not be interpreted as medically confirmed injuries. References to the consensus statements have been added to situate our approach within existing standards.
2. Concern: Reported “incidence rates” are not true epidemiological measures
Response: We appreciate this important point. To avoid misinterpretation, we have replaced the term “incidence rates” with “observed event frequencies” throughout the manuscript.
In the Title, we changed “Injury incidence” by “observed event frequencies”.
In the Methods section, we now specify that the reported numbers represent descriptive counts of stoppages associated with apparent discomfort rather than epidemiological injury rates.
In the Results and Discussion sections, we emphasize that these values should be interpreted as descriptive indicators rather than epidemiological measures.

3. Concern: Absence of training data, warm-up incidents, injury severity, severity, diagnostic confirmation, and return-to-play outcomes
Response: We recognize the absence of training surveillance, injury severity grading, and return-to-play outcomes as important limitations. We have added explicit statements in the Methods and Discussion sections, noting that such data were not available within the scope of this study. In the Limitations subsection, we explaine that this precludes direct comparison with consensus-based epidemiological studies and that these omissions reflect feasibility constraints inherent to AFCON tournaments, where access to centralized medical surveillance data is limited.

4. Concern: Framing of the study as epidemiology
Response: We agree that our initial framing overstated the scope of the work. The manuscript has been revised to present the study as exploratory and hypothesis-generating. The title, abstract, and introduction section have been reframed to emphasize that our work provides descriptive insights into match events at AFCON, complementing rather than replacing consensus-based injury surveillance systems. The Discussion section explicitly acknowledges this positioning, clarifying that our findings are descriptive indicators and should not be considered definitive epidemiological estimates.
Competing Interests: No competing interests were disclosed. Close
Report a concern

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Reviewer Report 30 Jan 2025

Pablo Prieto González, Prince Sultan University, Riyadh, Riyadh Province, Saudi Arabia

Not Approved

https://doi.org/10.5256/f1000research.176730.r358773

I consider that the article is not index for the following reasons:
The study demonstrates methodological weaknesses, as it relies solely on video-based analysis without incorporating direct player medical data or confirmed injury diagnoses. This limitation compromises the accuracy and reliability of the findings. Additionally, the research lacks approval from an Institutional Review Board (IRB), a critical requirement for studies involving human subjects or their data, even when using publicly available footage. The rationale for relying exclusively on video footage is insufficient, and the potential biases—such as missed injuries or misclassification of mechanisms—are not adequately addressed. While the focus on the African Cup of Nations (AFCON) offers novelty, the observational approach used undermines the generalizability of the findings to broader contexts or injury prevention strategies.
I regret not being more positive on this occasion.

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Sports training and injury prevention

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Version 1

VERSION 1

PUBLISHED 25 Apr 2024

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Reviewer Report 13 Sep 2024

Pablo Prieto González, Prince Sultan University, Riyadh, Riyadh Province, Saudi Arabia

Not Approved

https://doi.org/10.5256/f1000research.162439.r300243

Thank you very much for giving me the opportunity to review this study. Below, I share my observations regarding the manuscript in each of its sections:

INTRODUCCIÓN:
The introduction of the article "Injury incidence and associated factors among soccer players during the 2021 African Cup of Nations competition" presents strengths and areas for improvement. Among the strengths, it provides relevant context, highlighting the popularity of soccer and the large number of registered players both in Africa and worldwide, establishing the importance of the study within the global soccer landscape. Additionally, the introduction underscores the relevance of epidemiological studies in sports medicine, both for enhancing athletic performance and for developing injury prevention programs. It also mentions that injury characteristics can vary according to geographical factors such as climate and competition type, reinforcing the need for specific data to implement effective preventive measures. A comparative analysis of injury rates in various competitions, both national and international, contextualizes the severity and variability of the issue. Finally, the introduction identifies a research gap: the lack of studies on injury characteristics in African Cup of Nations (AFCON) tournaments, justifying the study's objective.

However, the introduction has several weaknesses. Some parts of the introduction could be clearer to improve understanding. Although geographical differences in injury incidence are mentioned, the study could developed deeper into how these differences influence the nature of injuries and the need for specific studies in different regions. It would be beneficial to provide more specific background on AFCON, highlighting its importance in the context of African and global soccer, to strengthen the study's justification. The transition to the study objectives could be smoother, improving the connection between identifying the research gap and the study's objectives for a more natural flow. There is room to improve clarity and particularly in depth in key aspects. Additionally, studying a previously unexamined population (players participating in the African Cup of Nations) does not constitute a novelty in itself unless it provides new insights into scientific knowledge.

METHODS:
Regarding the type of study, it is indicated as an analytical study. While this is not incorrect, it would be more accurate to specify that this is a video-based descriptive observational study. The STROBE-SIIS guidelines recommend providing a clear and detailed description of the study design, including the process for selecting injury events.

Regarding the statement that "there was no need for an ethical committee approval," it is important to emphasize that ethical approval is necessary to protect the privacy and rights of the players, ensure informed consent, minimize potential harm, and comply with ethical regulations and guidelines. Review by an ethics committee provides an independent evaluation and ensures that the study is conducted in an ethical and responsible manner.

Inclusion and Exclusion Criteria:
Specific inclusion and exclusion criteria for injury events are not detailed. It is essential to specify these criteria to understand how it was determined which injuries were included in the analysis.

Clearly Defined Outcomes:
The definition of an injury incident is relatively general. STROBE-SIIS suggests clearly defining specific outcomes and justifying the criteria used. In this study, the definition of a "situation in which the match was interrupted" may be ambiguous.

Sample Size Rationale:
No justification is provided for the sample size or the formula used to calculate it. STROBE-SIIS recommends describing how the sample size was determined and providing adequate statistical justification for this.

Variable Details:
While some characteristics of the injuries and players are mentioned, a detailed description of all variables considered in the analysis is missing. STROBE-SIIS emphasizes the importance of accurately specifying and categorizing all variables. I consider that one of the main limitations of the study is the small number of variables studied, and the absence of a clear criterion to analyze in depth the mechanisms that cause injuries.

Data Collection Methodology:
The data collection methodology is based on observing live broadcasts and replays, but specific tools or methods used to ensure consistency and accuracy in data collection are not detailed. STROBE-SIIS suggests providing a detailed description of data collection methods, including any standardized tools or protocols used.

Data Validation and Reliability:
There is no mention of how the reliability of the data collected by the consulting physicians was validated. STROBE-SIIS recommends describing any validation processes or reliability tests applied to the data.

Data Analysis and Statistical Considerations:
Although some statistical analyses are described, there is a lack of justification for the choice of statistical tests used. STROBE-SIIS suggests providing a clear justification for the statistical techniques employed and explaining how potential confounders were addressed.

Bias Information:
Possible sources of bias and how they were addressed are not discussed. STROBE-SIIS recommends identifying and discussing potential sources of bias in the study and the strategies used to minimize them.

Context and Confounding Data:
Not enough information is provided on potential confounding factors, such as exact weather conditions or the previous physical condition of the players. STROBE-SIIS suggests considering and adjusting for potential confounders in the analysis.

RESULTS
The lack of clear definitions and criteria in the methodology section affects the results section. Although data on injuries are presented, there is no clear definition of the criteria used for injury categorization. While it specifies that injuries were either contact or non-contact and further breaks down the analysis by injury location and timing, the specific criteria for including injuries in the dataset are not detailed. This lack of clarity may hinder the evaluation of the validity and reliability of the findings.

Inconsistent Data Presentation:
Some data are presented as means with standard deviations while others are presented as medians with interquartile ranges, and the rationale for choosing these methods is not explained. For example, the choice of using the median for playing time should be justified, as the standard deviation is used for other continuous variables. The inconsistency in data presentation could affect the interpretability and comparability of the results.

Absence of Statistical Power Analysis:
The results section lacks information on statistical power analysis, which is essential to determine whether the sample size was adequate to detect significant differences. There is no mention of how the sample size was determined or justified, which could raise concerns about the validity of the statistical comparisons made.

Potential Bias in Injury Reporting:
The results indicate that injuries were recorded and analyzed, but there is no discussion of potential biases in injury reporting. For example, whether all injuries were uniformly reported and categorized, or if there was any observer bias in the injury assessment process, is not addressed.

Limited Information on Contextual Factors:
Factors such as weather conditions, listed as temperature and humidity, are mentioned but not thoroughly analyzed in relation to injury incidence. The impact of these variables should be examined more comprehensively to understand their effect on injury rates. Additionally, there is a lack of analysis regarding confounding factors such as player fatigue or previous injuries.

Inadequate Analysis of Injury Mechanisms:
While the results provide a general breakdown of injury mechanisms (contact vs. non-contact) and their occurrence by match time, there is a lack of detailed analysis of how different mechanisms relate to specific injury types or player positions. A more detailed examination could help in understanding injury patterns more comprehensively.

Inadequate Analysis of Injury Impact:
Although the results show variations in injury rates by match round and time, there is limited analysis of how these injuries affected player performance and match outcomes. The study does not explore how injuries impacted player availability or team performance, which could provide valuable insights into the broader implications of the findings.

DISCUSSION AND CONCLUSION
One of the main shortcomings is the lack of consideration for injuries occurring during training sessions, warm-ups, and cool-downs. This is a significant limitation, as injuries during these periods can substantially contribute to the overall injury burden. Excluding these injuries from the study may lead to an underestimation of the total incidence and severity of injuries, affecting the comprehensiveness of the findings.

Additionally, the study does not report on the severity of the injuries or the duration of recovery. This omission is critical, as understanding the severity and recovery time of injuries provides crucial information on the injury burden and the long-term impact on players' health and performance.

The study compares injury rates with several previous studies but does not delve deeply into the potential differences in study methodologies, such as variations in injury definitions, data collection methods, or competitive environments. These differences may introduce inconsistencies in comparative findings, making it difficult to draw definitive conclusions.

The video-based analysis used in the study may introduce selection bias if certain injuries were less likely to be recorded or if injuries involving some players were not reported. Dependence on video footage may also overlook injuries that occurred off-camera or were inadequately captured, affecting the accuracy of reported injury rates.

While the study reports injury rates by player position, it does not explore how different playing styles or positional demands might contribute to the observed injury patterns. Understanding these factors could provide a more nuanced view of injury risks associated with different player positions.

The study highlights differences between players from different leagues (NALP vs. ALP) but does not thoroughly investigate how geographical or cultural differences in training practices might influence injury patterns. These differences could contribute to variations observed in injury mechanisms and types, but are not fully explored.

The study also does not address whether players or teams had access to specific injury prevention measures, such as strength and conditioning programs or medical interventions. The presence or absence of such measures could influence injury rates and should be considered when interpreting the results.

Despite presenting important limitations, the study does not thoroughly address the need for future research to address these shortcomings.

As for the conclusion, it must be taken into account that the findings are specific to the 2021 AFCON competition, and may not be generalizable to other tournaments or leagues. Factors such as competition level, player conditioning, and environmental conditions may vary, impacting the applicability of the conclusions to different contexts.

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

No
Are sufficient details of methods and analysis provided to allow replication by others?

No
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

References

1. Bahr R, Clarsen B, Derman W, Dvorak J, et al.: International Olympic Committee consensus statement: methods for recording and reporting of epidemiological data on injury and illness in sport 2020 (including STROBE Extension for Sport Injury and Illness Surveillance (STROBE-SIIS)).Br J Sports Med. 2020; 54 (7): 372-389 PubMed Abstract | Publisher Full Text

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Sports training and injury prevention

CITE

Report a concern

Author Response 13 Jan 2025

Anis Jellad, Physical Medicine and Rehabilitation, Faculty of Medicine University of Monastir, Monastir, 5000, Tunisia

13 Jan 2025

Author Response
Reviewer comments
Response

Comment: Although geographical differences in injury incidence are mentioned, the study could developed deeper into how these differences influence the nature of injuries and the need ... Continue reading
Reviewer comments
Response

Comment: Although geographical differences in injury incidence are mentioned, the study could developed deeper into how these differences influence the nature of injuries and the need for specific studies in different regions.
Response: As suggested, we added an example illustrating the influence of climate differences on injury nature.

Comment: It would be beneficial to provide more specific background on AFCON, highlighting its importance in the context of African and global soccer, to strengthen the study's justification.
Response: As suggested, we have added additional details about AFCON's significance, positioning it as a key tournament that features both local talent and international stars. Its importance for African football and global soccer development is emphasized, supporting the study's relevance.

Comment: The transition to the study objectives could be smoother, improving the connection between identifying the research gap and the study's objectives for a more natural flow. There is room to improve clarity and particularly in depth in key aspects. Additionally, studying a previously unexamined population (players participating in the African Cup of Nations) does not constitute a novelty in itself unless it provides new insights into scientific knowledge.
Response: We appreciate the reviewer's feedback on improving the flow and clarity. In response, we have refined the transition to better connect the identified research gap with the study’s objectives. We have also emphasized how this study contributes novel insights into injury epidemiology within the unique context of AFCON, offering valuable information for both regional and international injury prevention strategies.

Comment: Regarding the type of study, it is indicated as an analytical study. While this is not incorrect, it would be more accurate to specify that this is a video-based descriptive observational study.
Response: As suggested, the study design has been clearly redefined as a "video-based descriptive observational study" to align with reviewer recommendations and clarify the methodology.

Comment: The STROBE-SIIS guidelines recommend providing a clear and detailed description of the study design, including the process for selecting injury events.
Response: According to the STROBE-SIIS guidelines:

“SIIS-4.1. Clearly specify which health problems are being observed”: this item is explained lines 122-125.

SIIS-4.2. State explicitly which approach was used to record the health problem data, including all outcome measures or tools: this item is detailed lines 117-121.

SIIS-4.3.State explicitly which coding system was used to classify the health problems: lines 129-131

SIIS-4.4. Where relevant, clearly describe how athletes were categorised: players were categorised based Player's age, playing position, and the league where the footballer was playing in at the moment of the competition (NALP or ALP); lines 127-128.

Comment: Regarding the statement that "there was no need for an ethical committee approval," it is important to emphasize that ethical approval is necessary to protect the privacy and rights of the players, ensure informed consent, minimize potential harm, and comply with ethical regulations and guidelines. Review by an ethics committee provides an independent evaluation and ensures that the study is conducted in an ethical and responsible manner.
Response: We stated that ethical approval was not required as the data were sourced from publicly available video footage. Additionally, the identities of the players were not disclosed (lines 114–115).

Comment: Inclusion and Exclusion Criteria:
Specific inclusion and exclusion criteria for injury events are not detailed. It is essential to specify these criteria to understand how it was determined which injuries were included in the analysis.
Response: As suggested, we added an inclusion/exclusion criteria.

Comment: Clearly Defined Outcomes:
The definition of an injury incident is relatively general. STROBE-SIIS suggests clearly defining specific outcomes and justifying the criteria used. In this study, the definition of a "situation in which the match was interrupted" may be ambiguous.
Response: As suggested, we reformulated the injury definition in order to raise ambiguity.

Comment: Sample Size Rationale:
No justification is provided for the sample size or the formula used to calculate it. STROBE-SIIS recommends describing how the sample size was determined and providing adequate statistical justification for this.
Response: Sample size calculation was unnecessary, as all players participating in the tournament were included. In our case we conducted a population study.

Comment: Variable Details:
While some characteristics of the injuries and players are mentioned, a detailed description of all variables considered in the analysis is missing. STROBE-SIIS emphasizes the importance of accurately specifying and categorizing all variables. I consider that one of the main limitations of the study is the small number of variables studied, and the absence of a clear criterion to analyze in depth the mechanisms that cause injuries.
Response: As suggested, we added a detailed description of missing variables. We reviewer for his valuable remark.

Comment: Data Collection Methodology:
The data collection methodology is based on observing live broadcasts and replays, but specific tools or methods used to ensure consistency and accuracy in data collection are not detailed. STROBE-SIIS suggests providing a detailed description of data collection methods, including any standardized tools or protocols used.
Response: We thank the reviewer for their remark. Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day.

Comment: Data Validation and Reliability:
There is no mention of how the reliability of the data collected by the consulting physicians was validated. STROBE-SIIS recommends describing any validation processes or reliability tests applied to the data.
Response: Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day. In case of discrepancy, the intervention of a third author (AK) was required.
Details were added in the text (lines 121-122)

Comment: Data Analysis and Statistical Considerations:
Although some statistical analyses are described, there is a lack of justification for the choice of statistical tests used. STROBE-SIIS suggests providing a clear justification for the statistical techniques employed and explaining how potential confounders were addressed.
Response: The authors thank the reviewer for their remark. For clarity, we have added a justification for the choice of statistical tests used.

Comment: Bias Information:
Possible sources of bias and how they were addressed are not discussed. STROBE-SIIS recommends identifying and discussing potential sources of bias in the study and the strategies used to minimize them.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Context and Confounding Data:
Not enough information is provided on potential confounding factors, such as exact weather conditions or the previous physical condition of the players. STROBE-SIIS suggests considering and adjusting for potential confounders in the analysis.
Response: We acknowledge the lack details about potential confounding factors like player fatigue are now addressed.

Comment: Although data on injuries are presented, there is no clear definition of the criteria used for injury categorization. While it specifies that injuries were either contact or non-contact and further breaks down the analysis by injury location and timing, the specific criteria for including injuries in the dataset are not detailed. This lack of clarity may hinder the evaluation of the validity and reliability of the findings.
Response: We thank the reviewer for their valuable remark. This issue has been addressed in the Methods section under the inclusion criteria.

Comment: Inconsistent Data Presentation:
Some data are presented as means with standard deviations while others are presented as medians with interquartile ranges, and the rationale for choosing these methods is not explained. For example, the choice of using the median for playing time should be justified, as the standard deviation is used for other continuous variables. The inconsistency in data presentation could affect the interpretability and comparability of the results.
Response: The mean and standard deviation are used when the distribution of data is approximately symmetrical. In contrast, the median and interquartile range are employed for skewed distributions, such as playing time, to better represent central tendency and variability. This approach ensures that the most appropriate statistical measures are used, enhancing the interpretability of the results.

Comment: Absence of Statistical Power Analysis:
The results section lacks information on statistical power analysis, which is essential to determine whether the sample size was adequate to detect significant differences. There is no mention of how the sample size was determined or justified, which could raise concerns about the validity of the statistical comparisons made.
Response: We acknowledge the reviewer's comment regarding the absence of a statistical power analysis. Due to the nature of the study, which analyzed all available injury data from the 2021 AFCON, conducting a formal power analysis was not feasible. The study sample reflects the entire population of players and matches from the tournament, providing a comprehensive dataset. While this limits our ability to perform a prospective power calculation, we believe that analyzing the complete dataset ensures that the study captures all relevant injury patterns and associations.

Comment: Potential Bias in Injury Reporting:
The results indicate that injuries were recorded and analyzed, but there is no discussion of potential biases in injury reporting. For example, whether all injuries were uniformly reported and categorized, or if there was any observer bias in the injury assessment process, is not addressed.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Limited Information on Contextual Factors:
Factors such as weather conditions, listed as temperature and humidity, are mentioned but not thoroughly analyzed in relation to injury incidence. The impact of these variables should be examined more comprehensively to understand their effect on injury rates. Additionally, there is a lack of analysis regarding confounding factors such as player fatigue or previous injuries.
Response: Weather conditions (temperature and humidity) have been analyzed, we haven’t find a relationship with injury incidence. We acknowledge the lack of analysis regarding confounding factors such as player fatigue or previous injuries

Comment: Inadequate Analysis of Injury Mechanisms:
While the results provide a general breakdown of injury mechanisms (contact vs. non-contact) and their occurrence by match time, there is a lack of detailed analysis of how different mechanisms relate to specific injury types or player positions. A more detailed examination could help in understanding injury patterns more comprehensively.
Response: The analysis of injury mechanisms has been expanded to explore how different player positions and match contexts influence injury patterns.

Comment: Inadequate Analysis of Injury Impact:
Although the results show variations in injury rates by match round and time, there is limited analysis of how these injuries affected player performance and match outcomes. The study does not explore how injuries impacted player availability or team performance, which could provide valuable insights into the broader implications of the findings.
Response: As suggested, we included a discussion on how injuries impacted player availability and potential performance in subsequent matches.

Comment: One of the main shortcomings is the lack of consideration for injuries ocurring during training sessions, warm-ups, and cool-downs. This is a significant limitation, as injuries during these periods can substantially contribute to the overall injury burden. Excluding these injuries from the study may lead to an underestimation of the total incidence and severity of injuries, affecting the comprehensiveness of the findings.
Response: We acknowledge this limitation and discuss how it may underestimate the total injury burden, suggesting it as an area for future research.

Comment: Additionally, the study does not report on the severity of the injuries or the duration of recovery. This omission is critical, as understanding the severity and recovery time of injuries provides crucial information on the injury burden and the long-term impact on players' health and performance.
Response: We address this limitation, indicating the need for future studies to incorporate data on injury severity and recovery time to better understand the overall burden.

Comment: The study compares injury rates with several previous studies but does not delve deeply into the potential differences in study methodologies, such as variations in injury definitions, data collection methods, or competitive environments. These differences may introduce inconsistencies in comparative findings, making it difficult to draw definitive conclusions.
Response: A discussion has been added to compare methodologies between this study and others, including how different definitions of injury and data collection techniques may influence findings.

Comment: The video-based analysis used in the study may introduce selection bias if certain injuries were less likely to be recorded or if injuries involving some players were not reported. Dependence on video footage may also overlook injuries that occurred off-camera or were inadequately captured, affecting the accuracy of reported injury rates.
Response: As suggested, some injuries may be not recorded, this discussion is added in limitation section

Comment: While the study reports injury rates by player position, it does not explore how different playing styles or positional demands might contribute to the observed injury patterns. Understanding these factors could provide a more nuanced view of injury risks associated with different player positions.
Response: As suggested, we provide a more detailed discussion of how different playing styles and positional demands may explain variations in injury patterns across player roles.

Comment: The study highlights differences between players from different leagues (NALP vs. ALP) but does not thoroughly investigate how geographical or cultural differences in training practices might influence injury patterns. These differences could contribute to variations observed in injury mechanisms and types, but are not fully explored.
Response: we acknowledge that differences in training loads, intensity, and preparation between African and non-African league players (ALP vs. NALP) could contribute to variations in injury mechanisms, this was beyond the scope of our current analysis. However, we have added a discussion in the manuscript, noting that future research should explore how regional training practices, competition schedules, and recovery protocols may impact injury risk and mechanisms, potentially contributing to the observed differences between ALP and NALP players.

Comment: The study also does not address whether players or teams had access to specific injury prevention measures, such as strength and conditioning programs or medical interventions. The presence or absence of such measures could influence injury rates and should be considered when interpreting the results.
Response: While detailed data on prevention measures were unavailable, we recommend that future studies investigate the influence of training and medical interventions on injury rates.

Comment: Despite presenting important limitations, the study does not thoroughly address the need for future research to address these shortcomings.
Response: A section on future research is included, emphasizing the need to study injury prevention strategies, the role of training, and to include training and warm-up injury data.
Reviewer comments
Response

Comment: Although geographical differences in injury incidence are mentioned, the study could developed deeper into how these differences influence the nature of injuries and the need for specific studies in different regions.
Response: As suggested, we added an example illustrating the influence of climate differences on injury nature.

Comment: It would be beneficial to provide more specific background on AFCON, highlighting its importance in the context of African and global soccer, to strengthen the study's justification.
Response: As suggested, we have added additional details about AFCON's significance, positioning it as a key tournament that features both local talent and international stars. Its importance for African football and global soccer development is emphasized, supporting the study's relevance.

Comment: The transition to the study objectives could be smoother, improving the connection between identifying the research gap and the study's objectives for a more natural flow. There is room to improve clarity and particularly in depth in key aspects. Additionally, studying a previously unexamined population (players participating in the African Cup of Nations) does not constitute a novelty in itself unless it provides new insights into scientific knowledge.
Response: We appreciate the reviewer's feedback on improving the flow and clarity. In response, we have refined the transition to better connect the identified research gap with the study’s objectives. We have also emphasized how this study contributes novel insights into injury epidemiology within the unique context of AFCON, offering valuable information for both regional and international injury prevention strategies.

Comment: Regarding the type of study, it is indicated as an analytical study. While this is not incorrect, it would be more accurate to specify that this is a video-based descriptive observational study.
Response: As suggested, the study design has been clearly redefined as a "video-based descriptive observational study" to align with reviewer recommendations and clarify the methodology.

Comment: The STROBE-SIIS guidelines recommend providing a clear and detailed description of the study design, including the process for selecting injury events.
Response: According to the STROBE-SIIS guidelines:

“SIIS-4.1. Clearly specify which health problems are being observed”: this item is explained lines 122-125.

SIIS-4.2. State explicitly which approach was used to record the health problem data, including all outcome measures or tools: this item is detailed lines 117-121.

SIIS-4.3.State explicitly which coding system was used to classify the health problems: lines 129-131

SIIS-4.4. Where relevant, clearly describe how athletes were categorised: players were categorised based Player's age, playing position, and the league where the footballer was playing in at the moment of the competition (NALP or ALP); lines 127-128.

Comment: Regarding the statement that "there was no need for an ethical committee approval," it is important to emphasize that ethical approval is necessary to protect the privacy and rights of the players, ensure informed consent, minimize potential harm, and comply with ethical regulations and guidelines. Review by an ethics committee provides an independent evaluation and ensures that the study is conducted in an ethical and responsible manner.
Response: We stated that ethical approval was not required as the data were sourced from publicly available video footage. Additionally, the identities of the players were not disclosed (lines 114–115).

Comment: Inclusion and Exclusion Criteria:
Specific inclusion and exclusion criteria for injury events are not detailed. It is essential to specify these criteria to understand how it was determined which injuries were included in the analysis.
Response: As suggested, we added an inclusion/exclusion criteria.

Comment: Clearly Defined Outcomes:
The definition of an injury incident is relatively general. STROBE-SIIS suggests clearly defining specific outcomes and justifying the criteria used. In this study, the definition of a "situation in which the match was interrupted" may be ambiguous.
Response: As suggested, we reformulated the injury definition in order to raise ambiguity.

Comment: Sample Size Rationale:
No justification is provided for the sample size or the formula used to calculate it. STROBE-SIIS recommends describing how the sample size was determined and providing adequate statistical justification for this.
Response: Sample size calculation was unnecessary, as all players participating in the tournament were included. In our case we conducted a population study.

Comment: Variable Details:
While some characteristics of the injuries and players are mentioned, a detailed description of all variables considered in the analysis is missing. STROBE-SIIS emphasizes the importance of accurately specifying and categorizing all variables. I consider that one of the main limitations of the study is the small number of variables studied, and the absence of a clear criterion to analyze in depth the mechanisms that cause injuries.
Response: As suggested, we added a detailed description of missing variables. We reviewer for his valuable remark.

Comment: Data Collection Methodology:
The data collection methodology is based on observing live broadcasts and replays, but specific tools or methods used to ensure consistency and accuracy in data collection are not detailed. STROBE-SIIS suggests providing a detailed description of data collection methods, including any standardized tools or protocols used.
Response: We thank the reviewer for their remark. Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day.

Comment: Data Validation and Reliability:
There is no mention of how the reliability of the data collected by the consulting physicians was validated. STROBE-SIIS recommends describing any validation processes or reliability tests applied to the data.
Response: Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day. In case of discrepancy, the intervention of a third author (AK) was required.
Details were added in the text (lines 121-122)

Comment: Data Analysis and Statistical Considerations:
Although some statistical analyses are described, there is a lack of justification for the choice of statistical tests used. STROBE-SIIS suggests providing a clear justification for the statistical techniques employed and explaining how potential confounders were addressed.
Response: The authors thank the reviewer for their remark. For clarity, we have added a justification for the choice of statistical tests used.

Comment: Bias Information:
Possible sources of bias and how they were addressed are not discussed. STROBE-SIIS recommends identifying and discussing potential sources of bias in the study and the strategies used to minimize them.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Context and Confounding Data:
Not enough information is provided on potential confounding factors, such as exact weather conditions or the previous physical condition of the players. STROBE-SIIS suggests considering and adjusting for potential confounders in the analysis.
Response: We acknowledge the lack details about potential confounding factors like player fatigue are now addressed.

Comment: Although data on injuries are presented, there is no clear definition of the criteria used for injury categorization. While it specifies that injuries were either contact or non-contact and further breaks down the analysis by injury location and timing, the specific criteria for including injuries in the dataset are not detailed. This lack of clarity may hinder the evaluation of the validity and reliability of the findings.
Response: We thank the reviewer for their valuable remark. This issue has been addressed in the Methods section under the inclusion criteria.

Comment: Inconsistent Data Presentation:
Some data are presented as means with standard deviations while others are presented as medians with interquartile ranges, and the rationale for choosing these methods is not explained. For example, the choice of using the median for playing time should be justified, as the standard deviation is used for other continuous variables. The inconsistency in data presentation could affect the interpretability and comparability of the results.
Response: The mean and standard deviation are used when the distribution of data is approximately symmetrical. In contrast, the median and interquartile range are employed for skewed distributions, such as playing time, to better represent central tendency and variability. This approach ensures that the most appropriate statistical measures are used, enhancing the interpretability of the results.

Comment: Absence of Statistical Power Analysis:
The results section lacks information on statistical power analysis, which is essential to determine whether the sample size was adequate to detect significant differences. There is no mention of how the sample size was determined or justified, which could raise concerns about the validity of the statistical comparisons made.
Response: We acknowledge the reviewer's comment regarding the absence of a statistical power analysis. Due to the nature of the study, which analyzed all available injury data from the 2021 AFCON, conducting a formal power analysis was not feasible. The study sample reflects the entire population of players and matches from the tournament, providing a comprehensive dataset. While this limits our ability to perform a prospective power calculation, we believe that analyzing the complete dataset ensures that the study captures all relevant injury patterns and associations.

Comment: Potential Bias in Injury Reporting:
The results indicate that injuries were recorded and analyzed, but there is no discussion of potential biases in injury reporting. For example, whether all injuries were uniformly reported and categorized, or if there was any observer bias in the injury assessment process, is not addressed.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Limited Information on Contextual Factors:
Factors such as weather conditions, listed as temperature and humidity, are mentioned but not thoroughly analyzed in relation to injury incidence. The impact of these variables should be examined more comprehensively to understand their effect on injury rates. Additionally, there is a lack of analysis regarding confounding factors such as player fatigue or previous injuries.
Response: Weather conditions (temperature and humidity) have been analyzed, we haven’t find a relationship with injury incidence. We acknowledge the lack of analysis regarding confounding factors such as player fatigue or previous injuries

Comment: Inadequate Analysis of Injury Mechanisms:
While the results provide a general breakdown of injury mechanisms (contact vs. non-contact) and their occurrence by match time, there is a lack of detailed analysis of how different mechanisms relate to specific injury types or player positions. A more detailed examination could help in understanding injury patterns more comprehensively.
Response: The analysis of injury mechanisms has been expanded to explore how different player positions and match contexts influence injury patterns.

Comment: Inadequate Analysis of Injury Impact:
Although the results show variations in injury rates by match round and time, there is limited analysis of how these injuries affected player performance and match outcomes. The study does not explore how injuries impacted player availability or team performance, which could provide valuable insights into the broader implications of the findings.
Response: As suggested, we included a discussion on how injuries impacted player availability and potential performance in subsequent matches.

Comment: One of the main shortcomings is the lack of consideration for injuries ocurring during training sessions, warm-ups, and cool-downs. This is a significant limitation, as injuries during these periods can substantially contribute to the overall injury burden. Excluding these injuries from the study may lead to an underestimation of the total incidence and severity of injuries, affecting the comprehensiveness of the findings.
Response: We acknowledge this limitation and discuss how it may underestimate the total injury burden, suggesting it as an area for future research.

Comment: Additionally, the study does not report on the severity of the injuries or the duration of recovery. This omission is critical, as understanding the severity and recovery time of injuries provides crucial information on the injury burden and the long-term impact on players' health and performance.
Response: We address this limitation, indicating the need for future studies to incorporate data on injury severity and recovery time to better understand the overall burden.

Comment: The study compares injury rates with several previous studies but does not delve deeply into the potential differences in study methodologies, such as variations in injury definitions, data collection methods, or competitive environments. These differences may introduce inconsistencies in comparative findings, making it difficult to draw definitive conclusions.
Response: A discussion has been added to compare methodologies between this study and others, including how different definitions of injury and data collection techniques may influence findings.

Comment: The video-based analysis used in the study may introduce selection bias if certain injuries were less likely to be recorded or if injuries involving some players were not reported. Dependence on video footage may also overlook injuries that occurred off-camera or were inadequately captured, affecting the accuracy of reported injury rates.
Response: As suggested, some injuries may be not recorded, this discussion is added in limitation section

Comment: While the study reports injury rates by player position, it does not explore how different playing styles or positional demands might contribute to the observed injury patterns. Understanding these factors could provide a more nuanced view of injury risks associated with different player positions.
Response: As suggested, we provide a more detailed discussion of how different playing styles and positional demands may explain variations in injury patterns across player roles.

Comment: The study highlights differences between players from different leagues (NALP vs. ALP) but does not thoroughly investigate how geographical or cultural differences in training practices might influence injury patterns. These differences could contribute to variations observed in injury mechanisms and types, but are not fully explored.
Response: we acknowledge that differences in training loads, intensity, and preparation between African and non-African league players (ALP vs. NALP) could contribute to variations in injury mechanisms, this was beyond the scope of our current analysis. However, we have added a discussion in the manuscript, noting that future research should explore how regional training practices, competition schedules, and recovery protocols may impact injury risk and mechanisms, potentially contributing to the observed differences between ALP and NALP players.

Comment: The study also does not address whether players or teams had access to specific injury prevention measures, such as strength and conditioning programs or medical interventions. The presence or absence of such measures could influence injury rates and should be considered when interpreting the results.
Response: While detailed data on prevention measures were unavailable, we recommend that future studies investigate the influence of training and medical interventions on injury rates.

Comment: Despite presenting important limitations, the study does not thoroughly address the need for future research to address these shortcomings.
Response: A section on future research is included, emphasizing the need to study injury prevention strategies, the role of training, and to include training and warm-up injury data.
Competing Interests: No competing interests were disclosed. Close
Report a concern
Respond or Comment

COMMENTS ON THIS REPORT

Author Response 13 Jan 2025

Anis Jellad, Physical Medicine and Rehabilitation, Faculty of Medicine University of Monastir, Monastir, 5000, Tunisia

13 Jan 2025

Author Response
Reviewer comments
Response

Comment: Although geographical differences in injury incidence are mentioned, the study could developed deeper into how these differences influence the nature of injuries and the need ... Continue reading
Reviewer comments
Response

Comment: Although geographical differences in injury incidence are mentioned, the study could developed deeper into how these differences influence the nature of injuries and the need for specific studies in different regions.
Response: As suggested, we added an example illustrating the influence of climate differences on injury nature.

Comment: It would be beneficial to provide more specific background on AFCON, highlighting its importance in the context of African and global soccer, to strengthen the study's justification.
Response: As suggested, we have added additional details about AFCON's significance, positioning it as a key tournament that features both local talent and international stars. Its importance for African football and global soccer development is emphasized, supporting the study's relevance.

Comment: The transition to the study objectives could be smoother, improving the connection between identifying the research gap and the study's objectives for a more natural flow. There is room to improve clarity and particularly in depth in key aspects. Additionally, studying a previously unexamined population (players participating in the African Cup of Nations) does not constitute a novelty in itself unless it provides new insights into scientific knowledge.
Response: We appreciate the reviewer's feedback on improving the flow and clarity. In response, we have refined the transition to better connect the identified research gap with the study’s objectives. We have also emphasized how this study contributes novel insights into injury epidemiology within the unique context of AFCON, offering valuable information for both regional and international injury prevention strategies.

Comment: Regarding the type of study, it is indicated as an analytical study. While this is not incorrect, it would be more accurate to specify that this is a video-based descriptive observational study.
Response: As suggested, the study design has been clearly redefined as a "video-based descriptive observational study" to align with reviewer recommendations and clarify the methodology.

Comment: The STROBE-SIIS guidelines recommend providing a clear and detailed description of the study design, including the process for selecting injury events.
Response: According to the STROBE-SIIS guidelines:

“SIIS-4.1. Clearly specify which health problems are being observed”: this item is explained lines 122-125.

SIIS-4.2. State explicitly which approach was used to record the health problem data, including all outcome measures or tools: this item is detailed lines 117-121.

SIIS-4.3.State explicitly which coding system was used to classify the health problems: lines 129-131

SIIS-4.4. Where relevant, clearly describe how athletes were categorised: players were categorised based Player's age, playing position, and the league where the footballer was playing in at the moment of the competition (NALP or ALP); lines 127-128.

Comment: Regarding the statement that "there was no need for an ethical committee approval," it is important to emphasize that ethical approval is necessary to protect the privacy and rights of the players, ensure informed consent, minimize potential harm, and comply with ethical regulations and guidelines. Review by an ethics committee provides an independent evaluation and ensures that the study is conducted in an ethical and responsible manner.
Response: We stated that ethical approval was not required as the data were sourced from publicly available video footage. Additionally, the identities of the players were not disclosed (lines 114–115).

Comment: Inclusion and Exclusion Criteria:
Specific inclusion and exclusion criteria for injury events are not detailed. It is essential to specify these criteria to understand how it was determined which injuries were included in the analysis.
Response: As suggested, we added an inclusion/exclusion criteria.

Comment: Clearly Defined Outcomes:
The definition of an injury incident is relatively general. STROBE-SIIS suggests clearly defining specific outcomes and justifying the criteria used. In this study, the definition of a "situation in which the match was interrupted" may be ambiguous.
Response: As suggested, we reformulated the injury definition in order to raise ambiguity.

Comment: Sample Size Rationale:
No justification is provided for the sample size or the formula used to calculate it. STROBE-SIIS recommends describing how the sample size was determined and providing adequate statistical justification for this.
Response: Sample size calculation was unnecessary, as all players participating in the tournament were included. In our case we conducted a population study.

Comment: Variable Details:
While some characteristics of the injuries and players are mentioned, a detailed description of all variables considered in the analysis is missing. STROBE-SIIS emphasizes the importance of accurately specifying and categorizing all variables. I consider that one of the main limitations of the study is the small number of variables studied, and the absence of a clear criterion to analyze in depth the mechanisms that cause injuries.
Response: As suggested, we added a detailed description of missing variables. We reviewer for his valuable remark.

Comment: Data Collection Methodology:
The data collection methodology is based on observing live broadcasts and replays, but specific tools or methods used to ensure consistency and accuracy in data collection are not detailed. STROBE-SIIS suggests providing a detailed description of data collection methods, including any standardized tools or protocols used.
Response: We thank the reviewer for their remark. Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day.

Comment: Data Validation and Reliability:
There is no mention of how the reliability of the data collected by the consulting physicians was validated. STROBE-SIIS recommends describing any validation processes or reliability tests applied to the data.
Response: Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day. In case of discrepancy, the intervention of a third author (AK) was required.
Details were added in the text (lines 121-122)

Comment: Data Analysis and Statistical Considerations:
Although some statistical analyses are described, there is a lack of justification for the choice of statistical tests used. STROBE-SIIS suggests providing a clear justification for the statistical techniques employed and explaining how potential confounders were addressed.
Response: The authors thank the reviewer for their remark. For clarity, we have added a justification for the choice of statistical tests used.

Comment: Bias Information:
Possible sources of bias and how they were addressed are not discussed. STROBE-SIIS recommends identifying and discussing potential sources of bias in the study and the strategies used to minimize them.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Context and Confounding Data:
Not enough information is provided on potential confounding factors, such as exact weather conditions or the previous physical condition of the players. STROBE-SIIS suggests considering and adjusting for potential confounders in the analysis.
Response: We acknowledge the lack details about potential confounding factors like player fatigue are now addressed.

Comment: Although data on injuries are presented, there is no clear definition of the criteria used for injury categorization. While it specifies that injuries were either contact or non-contact and further breaks down the analysis by injury location and timing, the specific criteria for including injuries in the dataset are not detailed. This lack of clarity may hinder the evaluation of the validity and reliability of the findings.
Response: We thank the reviewer for their valuable remark. This issue has been addressed in the Methods section under the inclusion criteria.

Comment: Inconsistent Data Presentation:
Some data are presented as means with standard deviations while others are presented as medians with interquartile ranges, and the rationale for choosing these methods is not explained. For example, the choice of using the median for playing time should be justified, as the standard deviation is used for other continuous variables. The inconsistency in data presentation could affect the interpretability and comparability of the results.
Response: The mean and standard deviation are used when the distribution of data is approximately symmetrical. In contrast, the median and interquartile range are employed for skewed distributions, such as playing time, to better represent central tendency and variability. This approach ensures that the most appropriate statistical measures are used, enhancing the interpretability of the results.

Comment: Absence of Statistical Power Analysis:
The results section lacks information on statistical power analysis, which is essential to determine whether the sample size was adequate to detect significant differences. There is no mention of how the sample size was determined or justified, which could raise concerns about the validity of the statistical comparisons made.
Response: We acknowledge the reviewer's comment regarding the absence of a statistical power analysis. Due to the nature of the study, which analyzed all available injury data from the 2021 AFCON, conducting a formal power analysis was not feasible. The study sample reflects the entire population of players and matches from the tournament, providing a comprehensive dataset. While this limits our ability to perform a prospective power calculation, we believe that analyzing the complete dataset ensures that the study captures all relevant injury patterns and associations.

Comment: Potential Bias in Injury Reporting:
The results indicate that injuries were recorded and analyzed, but there is no discussion of potential biases in injury reporting. For example, whether all injuries were uniformly reported and categorized, or if there was any observer bias in the injury assessment process, is not addressed.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Limited Information on Contextual Factors:
Factors such as weather conditions, listed as temperature and humidity, are mentioned but not thoroughly analyzed in relation to injury incidence. The impact of these variables should be examined more comprehensively to understand their effect on injury rates. Additionally, there is a lack of analysis regarding confounding factors such as player fatigue or previous injuries.
Response: Weather conditions (temperature and humidity) have been analyzed, we haven’t find a relationship with injury incidence. We acknowledge the lack of analysis regarding confounding factors such as player fatigue or previous injuries

Comment: Inadequate Analysis of Injury Mechanisms:
While the results provide a general breakdown of injury mechanisms (contact vs. non-contact) and their occurrence by match time, there is a lack of detailed analysis of how different mechanisms relate to specific injury types or player positions. A more detailed examination could help in understanding injury patterns more comprehensively.
Response: The analysis of injury mechanisms has been expanded to explore how different player positions and match contexts influence injury patterns.

Comment: Inadequate Analysis of Injury Impact:
Although the results show variations in injury rates by match round and time, there is limited analysis of how these injuries affected player performance and match outcomes. The study does not explore how injuries impacted player availability or team performance, which could provide valuable insights into the broader implications of the findings.
Response: As suggested, we included a discussion on how injuries impacted player availability and potential performance in subsequent matches.

Comment: One of the main shortcomings is the lack of consideration for injuries ocurring during training sessions, warm-ups, and cool-downs. This is a significant limitation, as injuries during these periods can substantially contribute to the overall injury burden. Excluding these injuries from the study may lead to an underestimation of the total incidence and severity of injuries, affecting the comprehensiveness of the findings.
Response: We acknowledge this limitation and discuss how it may underestimate the total injury burden, suggesting it as an area for future research.

Comment: Additionally, the study does not report on the severity of the injuries or the duration of recovery. This omission is critical, as understanding the severity and recovery time of injuries provides crucial information on the injury burden and the long-term impact on players' health and performance.
Response: We address this limitation, indicating the need for future studies to incorporate data on injury severity and recovery time to better understand the overall burden.

Comment: The study compares injury rates with several previous studies but does not delve deeply into the potential differences in study methodologies, such as variations in injury definitions, data collection methods, or competitive environments. These differences may introduce inconsistencies in comparative findings, making it difficult to draw definitive conclusions.
Response: A discussion has been added to compare methodologies between this study and others, including how different definitions of injury and data collection techniques may influence findings.

Comment: The video-based analysis used in the study may introduce selection bias if certain injuries were less likely to be recorded or if injuries involving some players were not reported. Dependence on video footage may also overlook injuries that occurred off-camera or were inadequately captured, affecting the accuracy of reported injury rates.
Response: As suggested, some injuries may be not recorded, this discussion is added in limitation section

Comment: While the study reports injury rates by player position, it does not explore how different playing styles or positional demands might contribute to the observed injury patterns. Understanding these factors could provide a more nuanced view of injury risks associated with different player positions.
Response: As suggested, we provide a more detailed discussion of how different playing styles and positional demands may explain variations in injury patterns across player roles.

Comment: The study highlights differences between players from different leagues (NALP vs. ALP) but does not thoroughly investigate how geographical or cultural differences in training practices might influence injury patterns. These differences could contribute to variations observed in injury mechanisms and types, but are not fully explored.
Response: we acknowledge that differences in training loads, intensity, and preparation between African and non-African league players (ALP vs. NALP) could contribute to variations in injury mechanisms, this was beyond the scope of our current analysis. However, we have added a discussion in the manuscript, noting that future research should explore how regional training practices, competition schedules, and recovery protocols may impact injury risk and mechanisms, potentially contributing to the observed differences between ALP and NALP players.

Comment: The study also does not address whether players or teams had access to specific injury prevention measures, such as strength and conditioning programs or medical interventions. The presence or absence of such measures could influence injury rates and should be considered when interpreting the results.
Response: While detailed data on prevention measures were unavailable, we recommend that future studies investigate the influence of training and medical interventions on injury rates.

Comment: Despite presenting important limitations, the study does not thoroughly address the need for future research to address these shortcomings.
Response: A section on future research is included, emphasizing the need to study injury prevention strategies, the role of training, and to include training and warm-up injury data.
Reviewer comments
Response

Comment: Although geographical differences in injury incidence are mentioned, the study could developed deeper into how these differences influence the nature of injuries and the need for specific studies in different regions.
Response: As suggested, we added an example illustrating the influence of climate differences on injury nature.

Comment: It would be beneficial to provide more specific background on AFCON, highlighting its importance in the context of African and global soccer, to strengthen the study's justification.
Response: As suggested, we have added additional details about AFCON's significance, positioning it as a key tournament that features both local talent and international stars. Its importance for African football and global soccer development is emphasized, supporting the study's relevance.

Comment: The transition to the study objectives could be smoother, improving the connection between identifying the research gap and the study's objectives for a more natural flow. There is room to improve clarity and particularly in depth in key aspects. Additionally, studying a previously unexamined population (players participating in the African Cup of Nations) does not constitute a novelty in itself unless it provides new insights into scientific knowledge.
Response: We appreciate the reviewer's feedback on improving the flow and clarity. In response, we have refined the transition to better connect the identified research gap with the study’s objectives. We have also emphasized how this study contributes novel insights into injury epidemiology within the unique context of AFCON, offering valuable information for both regional and international injury prevention strategies.

Comment: Regarding the type of study, it is indicated as an analytical study. While this is not incorrect, it would be more accurate to specify that this is a video-based descriptive observational study.
Response: As suggested, the study design has been clearly redefined as a "video-based descriptive observational study" to align with reviewer recommendations and clarify the methodology.

Comment: The STROBE-SIIS guidelines recommend providing a clear and detailed description of the study design, including the process for selecting injury events.
Response: According to the STROBE-SIIS guidelines:

“SIIS-4.1. Clearly specify which health problems are being observed”: this item is explained lines 122-125.

SIIS-4.2. State explicitly which approach was used to record the health problem data, including all outcome measures or tools: this item is detailed lines 117-121.

SIIS-4.3.State explicitly which coding system was used to classify the health problems: lines 129-131

SIIS-4.4. Where relevant, clearly describe how athletes were categorised: players were categorised based Player's age, playing position, and the league where the footballer was playing in at the moment of the competition (NALP or ALP); lines 127-128.

Comment: Regarding the statement that "there was no need for an ethical committee approval," it is important to emphasize that ethical approval is necessary to protect the privacy and rights of the players, ensure informed consent, minimize potential harm, and comply with ethical regulations and guidelines. Review by an ethics committee provides an independent evaluation and ensures that the study is conducted in an ethical and responsible manner.
Response: We stated that ethical approval was not required as the data were sourced from publicly available video footage. Additionally, the identities of the players were not disclosed (lines 114–115).

Comment: Inclusion and Exclusion Criteria:
Specific inclusion and exclusion criteria for injury events are not detailed. It is essential to specify these criteria to understand how it was determined which injuries were included in the analysis.
Response: As suggested, we added an inclusion/exclusion criteria.

Comment: Clearly Defined Outcomes:
The definition of an injury incident is relatively general. STROBE-SIIS suggests clearly defining specific outcomes and justifying the criteria used. In this study, the definition of a "situation in which the match was interrupted" may be ambiguous.
Response: As suggested, we reformulated the injury definition in order to raise ambiguity.

Comment: Sample Size Rationale:
No justification is provided for the sample size or the formula used to calculate it. STROBE-SIIS recommends describing how the sample size was determined and providing adequate statistical justification for this.
Response: Sample size calculation was unnecessary, as all players participating in the tournament were included. In our case we conducted a population study.

Comment: Variable Details:
While some characteristics of the injuries and players are mentioned, a detailed description of all variables considered in the analysis is missing. STROBE-SIIS emphasizes the importance of accurately specifying and categorizing all variables. I consider that one of the main limitations of the study is the small number of variables studied, and the absence of a clear criterion to analyze in depth the mechanisms that cause injuries.
Response: As suggested, we added a detailed description of missing variables. We reviewer for his valuable remark.

Comment: Data Collection Methodology:
The data collection methodology is based on observing live broadcasts and replays, but specific tools or methods used to ensure consistency and accuracy in data collection are not detailed. STROBE-SIIS suggests providing a detailed description of data collection methods, including any standardized tools or protocols used.
Response: We thank the reviewer for their remark. Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day.

Comment: Data Validation and Reliability:
There is no mention of how the reliability of the data collected by the consulting physicians was validated. STROBE-SIIS recommends describing any validation processes or reliability tests applied to the data.
Response: Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day. In case of discrepancy, the intervention of a third author (AK) was required.
Details were added in the text (lines 121-122)

Comment: Data Analysis and Statistical Considerations:
Although some statistical analyses are described, there is a lack of justification for the choice of statistical tests used. STROBE-SIIS suggests providing a clear justification for the statistical techniques employed and explaining how potential confounders were addressed.
Response: The authors thank the reviewer for their remark. For clarity, we have added a justification for the choice of statistical tests used.

Comment: Bias Information:
Possible sources of bias and how they were addressed are not discussed. STROBE-SIIS recommends identifying and discussing potential sources of bias in the study and the strategies used to minimize them.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Context and Confounding Data:
Not enough information is provided on potential confounding factors, such as exact weather conditions or the previous physical condition of the players. STROBE-SIIS suggests considering and adjusting for potential confounders in the analysis.
Response: We acknowledge the lack details about potential confounding factors like player fatigue are now addressed.

Comment: Although data on injuries are presented, there is no clear definition of the criteria used for injury categorization. While it specifies that injuries were either contact or non-contact and further breaks down the analysis by injury location and timing, the specific criteria for including injuries in the dataset are not detailed. This lack of clarity may hinder the evaluation of the validity and reliability of the findings.
Response: We thank the reviewer for their valuable remark. This issue has been addressed in the Methods section under the inclusion criteria.

Comment: Inconsistent Data Presentation:
Some data are presented as means with standard deviations while others are presented as medians with interquartile ranges, and the rationale for choosing these methods is not explained. For example, the choice of using the median for playing time should be justified, as the standard deviation is used for other continuous variables. The inconsistency in data presentation could affect the interpretability and comparability of the results.
Response: The mean and standard deviation are used when the distribution of data is approximately symmetrical. In contrast, the median and interquartile range are employed for skewed distributions, such as playing time, to better represent central tendency and variability. This approach ensures that the most appropriate statistical measures are used, enhancing the interpretability of the results.

Comment: Absence of Statistical Power Analysis:
The results section lacks information on statistical power analysis, which is essential to determine whether the sample size was adequate to detect significant differences. There is no mention of how the sample size was determined or justified, which could raise concerns about the validity of the statistical comparisons made.
Response: We acknowledge the reviewer's comment regarding the absence of a statistical power analysis. Due to the nature of the study, which analyzed all available injury data from the 2021 AFCON, conducting a formal power analysis was not feasible. The study sample reflects the entire population of players and matches from the tournament, providing a comprehensive dataset. While this limits our ability to perform a prospective power calculation, we believe that analyzing the complete dataset ensures that the study captures all relevant injury patterns and associations.

Comment: Potential Bias in Injury Reporting:
The results indicate that injuries were recorded and analyzed, but there is no discussion of potential biases in injury reporting. For example, whether all injuries were uniformly reported and categorized, or if there was any observer bias in the injury assessment process, is not addressed.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Limited Information on Contextual Factors:
Factors such as weather conditions, listed as temperature and humidity, are mentioned but not thoroughly analyzed in relation to injury incidence. The impact of these variables should be examined more comprehensively to understand their effect on injury rates. Additionally, there is a lack of analysis regarding confounding factors such as player fatigue or previous injuries.
Response: Weather conditions (temperature and humidity) have been analyzed, we haven’t find a relationship with injury incidence. We acknowledge the lack of analysis regarding confounding factors such as player fatigue or previous injuries

Comment: Inadequate Analysis of Injury Mechanisms:
While the results provide a general breakdown of injury mechanisms (contact vs. non-contact) and their occurrence by match time, there is a lack of detailed analysis of how different mechanisms relate to specific injury types or player positions. A more detailed examination could help in understanding injury patterns more comprehensively.
Response: The analysis of injury mechanisms has been expanded to explore how different player positions and match contexts influence injury patterns.

Comment: Inadequate Analysis of Injury Impact:
Although the results show variations in injury rates by match round and time, there is limited analysis of how these injuries affected player performance and match outcomes. The study does not explore how injuries impacted player availability or team performance, which could provide valuable insights into the broader implications of the findings.
Response: As suggested, we included a discussion on how injuries impacted player availability and potential performance in subsequent matches.

Comment: One of the main shortcomings is the lack of consideration for injuries ocurring during training sessions, warm-ups, and cool-downs. This is a significant limitation, as injuries during these periods can substantially contribute to the overall injury burden. Excluding these injuries from the study may lead to an underestimation of the total incidence and severity of injuries, affecting the comprehensiveness of the findings.
Response: We acknowledge this limitation and discuss how it may underestimate the total injury burden, suggesting it as an area for future research.

Comment: Additionally, the study does not report on the severity of the injuries or the duration of recovery. This omission is critical, as understanding the severity and recovery time of injuries provides crucial information on the injury burden and the long-term impact on players' health and performance.
Response: We address this limitation, indicating the need for future studies to incorporate data on injury severity and recovery time to better understand the overall burden.

Comment: The study compares injury rates with several previous studies but does not delve deeply into the potential differences in study methodologies, such as variations in injury definitions, data collection methods, or competitive environments. These differences may introduce inconsistencies in comparative findings, making it difficult to draw definitive conclusions.
Response: A discussion has been added to compare methodologies between this study and others, including how different definitions of injury and data collection techniques may influence findings.

Comment: The video-based analysis used in the study may introduce selection bias if certain injuries were less likely to be recorded or if injuries involving some players were not reported. Dependence on video footage may also overlook injuries that occurred off-camera or were inadequately captured, affecting the accuracy of reported injury rates.
Response: As suggested, some injuries may be not recorded, this discussion is added in limitation section

Comment: While the study reports injury rates by player position, it does not explore how different playing styles or positional demands might contribute to the observed injury patterns. Understanding these factors could provide a more nuanced view of injury risks associated with different player positions.
Response: As suggested, we provide a more detailed discussion of how different playing styles and positional demands may explain variations in injury patterns across player roles.

Comment: The study highlights differences between players from different leagues (NALP vs. ALP) but does not thoroughly investigate how geographical or cultural differences in training practices might influence injury patterns. These differences could contribute to variations observed in injury mechanisms and types, but are not fully explored.
Response: we acknowledge that differences in training loads, intensity, and preparation between African and non-African league players (ALP vs. NALP) could contribute to variations in injury mechanisms, this was beyond the scope of our current analysis. However, we have added a discussion in the manuscript, noting that future research should explore how regional training practices, competition schedules, and recovery protocols may impact injury risk and mechanisms, potentially contributing to the observed differences between ALP and NALP players.

Comment: The study also does not address whether players or teams had access to specific injury prevention measures, such as strength and conditioning programs or medical interventions. The presence or absence of such measures could influence injury rates and should be considered when interpreting the results.
Response: While detailed data on prevention measures were unavailable, we recommend that future studies investigate the influence of training and medical interventions on injury rates.

Comment: Despite presenting important limitations, the study does not thoroughly address the need for future research to address these shortcomings.
Response: A section on future research is included, emphasizing the need to study injury prevention strategies, the role of training, and to include training and warm-up injury data.
Competing Interests: No competing interests were disclosed. Close
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Reviewer Report 14 Jun 2024

Fouad Chiha, Universite Constantine 2, Constantine, Constantine Province, Algeria

Approved

https://doi.org/10.5256/f1000research.162439.r281561

Knowing the epidemiology of footballer injuries during international competitions is essential for developing preventive strategies. The study compared its results to those linked to other international competitions. This study aimed to characterize injuries contracted during the African Cup of Nations (AFCON) in Cameroon from January 9 to February 6, 2021.

The study reports an injury incidence of 48.8 per 1000 match hours and a rate of 1.7 injuries per match. Muscle injuries were the highest and the main factors being advanced age and length of play.

In conclusion, the study highlights the importance of preventive interventions. Addressing the use of preventive sessions (the FMS test is the best example) and recognized prophylactic means would have been relevant to put forward practical recommendations based on the results of the study. When discussing the results, we must pay attention to the characteristics of the competitions to be compared (climate, timing, match schedule, number of participating teams, number of matches played) to better appreciate the comparisons.

Is the work clearly and accurately presented and does it cite the current literature?

Yes
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Training methodology –football- physical preparation- exercise physiology- monotoring..

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

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Version 3

VERSION 3 PUBLISHED 25 Apr 2024

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Reviewer Reports

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	1	2	3
Version 3 (revision) 31 Oct 25
Version 2 (revision) 13 Jan 25		read	read
Version 1 25 Apr 24	read	read

Fouad Chiha, Universite Constantine 2, Constantine, Algeria
Pablo Prieto González, Prince Sultan University, Riyadh, Saudi Arabia
Afxentios Kekelekis, Aristotle University of Thessaloniki, Serres, Greece

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Reviewer Report

10 Views

11 Sep 2025 | for Version 2

Afxentios Kekelekis, Aristotle University of Thessaloniki, Serres, Greece

10 Views Cite this report Responses(1)

Not Approved

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

No
Are sufficient details of methods and analysis provided to allow replication by others?

No
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

No
Are the conclusions drawn adequately supported by the results?

No

References

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Injury epidemiology, Injury risk analysis

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Responses (1)

Author Response

31 Oct 2025

Anis Jellad, Physical Medicine and Rehabilitation, Faculty of Medicine University of Monastir, Monastir, 5000, Tunisia

Dear Reviewer,
We sincerely thank you for your careful reading of our manuscript and for the constructive critiques, you have provided.
Your observations have been invaluable in helping us clarify the scope, strengthen the methodology section, and better situate our findings within the literature.
Below we provide a detailed, point-by-point response to the concerns raised.

1. Concern: Use of video analysis and non-consensus injury definition
Response: We agree with the reviewer that our injury definition does not follow the IOC/FIFA/UEFA consensus statements. To address this, we have clarified in the Methods section that our study is a video-coded event analysis rather than a medical injury surveillance study. We explicitly acknowledge in the Discussion section, that the coded events may include transient discomfort or tactical behavior and should not be interpreted as medically confirmed injuries. References to the consensus statements have been added to situate our approach within existing standards.
2. Concern: Reported “incidence rates” are not true epidemiological measures
Response: We appreciate this important point. To avoid misinterpretation, we have replaced the term “incidence rates” with “observed event frequencies” throughout the manuscript.
In the Title, we changed “Injury incidence” by “observed event frequencies”.
In the Methods section, we now specify that the reported numbers represent descriptive counts of stoppages associated with apparent discomfort rather than epidemiological injury rates.
In the Results and Discussion sections, we emphasize that these values should be interpreted as descriptive indicators rather than epidemiological measures.

3. Concern: Absence of training data, warm-up incidents, injury severity, severity, diagnostic confirmation, and return-to-play outcomes
Response: We recognize the absence of training surveillance, injury severity grading, and return-to-play outcomes as important limitations. We have added explicit statements in the Methods and Discussion sections, noting that such data were not available within the scope of this study. In the Limitations subsection, we explaine that this precludes direct comparison with consensus-based epidemiological studies and that these omissions reflect feasibility constraints inherent to AFCON tournaments, where access to centralized medical surveillance data is limited.

4. Concern: Framing of the study as epidemiology
Response: We agree that our initial framing overstated the scope of the work. The manuscript has been revised to present the study as exploratory and hypothesis-generating. The title, abstract, and introduction section have been reframed to emphasize that our work provides descriptive insights into match events at AFCON, complementing rather than replacing consensus-based injury surveillance systems. The Discussion section explicitly acknowledges this positioning, clarifying that our findings are descriptive indicators and should not be considered definitive epidemiological estimates.

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Competing Interests

No competing interests were disclosed.

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Reviewer Report

7 Views

30 Jan 2025 | for Version 2

Pablo Prieto González, Prince Sultan University, Riyadh, Riyadh Province, Saudi Arabia

7 Views Cite this report Responses(0)

Not Approved

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Sports training and injury prevention

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Reviewer Report

25 Views

13 Sep 2024 | for Version 1

Pablo Prieto González, Prince Sultan University, Riyadh, Riyadh Province, Saudi Arabia

25 Views Cite this report Responses(1)

Not Approved

Is the work clearly and accurately presented and does it cite the current literature?

No
Is the study design appropriate and is the work technically sound?

No
Are sufficient details of methods and analysis provided to allow replication by others?

No
If applicable, is the statistical analysis and its interpretation appropriate?

Partly
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

References

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Sports training and injury prevention

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Responses (1)

Author Response

13 Jan 2025

Anis Jellad, Physical Medicine and Rehabilitation, Faculty of Medicine University of Monastir, Monastir, 5000, Tunisia

Reviewer comments
Response

Comment: Although geographical differences in injury incidence are mentioned, the study could developed deeper into how these differences influence the nature of injuries and the need for specific studies in different regions.
Response: As suggested, we added an example illustrating the influence of climate differences on injury nature.

Comment: It would be beneficial to provide more specific background on AFCON, highlighting its importance in the context of African and global soccer, to strengthen the study's justification.
Response: As suggested, we have added additional details about AFCON's significance, positioning it as a key tournament that features both local talent and international stars. Its importance for African football and global soccer development is emphasized, supporting the study's relevance.

Comment: The transition to the study objectives could be smoother, improving the connection between identifying the research gap and the study's objectives for a more natural flow. There is room to improve clarity and particularly in depth in key aspects. Additionally, studying a previously unexamined population (players participating in the African Cup of Nations) does not constitute a novelty in itself unless it provides new insights into scientific knowledge.
Response: We appreciate the reviewer's feedback on improving the flow and clarity. In response, we have refined the transition to better connect the identified research gap with the study’s objectives. We have also emphasized how this study contributes novel insights into injury epidemiology within the unique context of AFCON, offering valuable information for both regional and international injury prevention strategies.

Comment: Regarding the type of study, it is indicated as an analytical study. While this is not incorrect, it would be more accurate to specify that this is a video-based descriptive observational study.
Response: As suggested, the study design has been clearly redefined as a "video-based descriptive observational study" to align with reviewer recommendations and clarify the methodology.

Comment: The STROBE-SIIS guidelines recommend providing a clear and detailed description of the study design, including the process for selecting injury events.
Response: According to the STROBE-SIIS guidelines:

“SIIS-4.1. Clearly specify which health problems are being observed”: this item is explained lines 122-125.
SIIS-4.2. State explicitly which approach was used to record the health problem data, including all outcome measures or tools: this item is detailed lines 117-121.
SIIS-4.3.State explicitly which coding system was used to classify the health problems: lines 129-131
SIIS-4.4. Where relevant, clearly describe how athletes were categorised: players were categorised based Player's age, playing position, and the league where the footballer was playing in at the moment of the competition (NALP or ALP); lines 127-128.

Comment: Regarding the statement that "there was no need for an ethical committee approval," it is important to emphasize that ethical approval is necessary to protect the privacy and rights of the players, ensure informed consent, minimize potential harm, and comply with ethical regulations and guidelines. Review by an ethics committee provides an independent evaluation and ensures that the study is conducted in an ethical and responsible manner.
Response: We stated that ethical approval was not required as the data were sourced from publicly available video footage. Additionally, the identities of the players were not disclosed (lines 114–115).

Comment: Inclusion and Exclusion Criteria:
Specific inclusion and exclusion criteria for injury events are not detailed. It is essential to specify these criteria to understand how it was determined which injuries were included in the analysis.
Response: As suggested, we added an inclusion/exclusion criteria.

Comment: Clearly Defined Outcomes:
The definition of an injury incident is relatively general. STROBE-SIIS suggests clearly defining specific outcomes and justifying the criteria used. In this study, the definition of a "situation in which the match was interrupted" may be ambiguous.
Response: As suggested, we reformulated the injury definition in order to raise ambiguity.

Comment: Sample Size Rationale:
No justification is provided for the sample size or the formula used to calculate it. STROBE-SIIS recommends describing how the sample size was determined and providing adequate statistical justification for this.
Response: Sample size calculation was unnecessary, as all players participating in the tournament were included. In our case we conducted a population study.

Comment: Variable Details:
While some characteristics of the injuries and players are mentioned, a detailed description of all variables considered in the analysis is missing. STROBE-SIIS emphasizes the importance of accurately specifying and categorizing all variables. I consider that one of the main limitations of the study is the small number of variables studied, and the absence of a clear criterion to analyze in depth the mechanisms that cause injuries.
Response: As suggested, we added a detailed description of missing variables. We reviewer for his valuable remark.

Comment: Data Collection Methodology:
The data collection methodology is based on observing live broadcasts and replays, but specific tools or methods used to ensure consistency and accuracy in data collection are not detailed. STROBE-SIIS suggests providing a detailed description of data collection methods, including any standardized tools or protocols used.
Response: We thank the reviewer for their remark. Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day.

Comment: Data Validation and Reliability:
There is no mention of how the reliability of the data collected by the consulting physicians was validated. STROBE-SIIS recommends describing any validation processes or reliability tests applied to the data.
Response: Injuries were registered by the two authors (AJ and AC) independently and outcomes were compared at the end of each competition day. In case of discrepancy, the intervention of a third author (AK) was required.
Details were added in the text (lines 121-122)

Comment: Data Analysis and Statistical Considerations:
Although some statistical analyses are described, there is a lack of justification for the choice of statistical tests used. STROBE-SIIS suggests providing a clear justification for the statistical techniques employed and explaining how potential confounders were addressed.
Response: The authors thank the reviewer for their remark. For clarity, we have added a justification for the choice of statistical tests used.

Comment: Bias Information:
Possible sources of bias and how they were addressed are not discussed. STROBE-SIIS recommends identifying and discussing potential sources of bias in the study and the strategies used to minimize them.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Context and Confounding Data:
Not enough information is provided on potential confounding factors, such as exact weather conditions or the previous physical condition of the players. STROBE-SIIS suggests considering and adjusting for potential confounders in the analysis.
Response: We acknowledge the lack details about potential confounding factors like player fatigue are now addressed.

Comment: Although data on injuries are presented, there is no clear definition of the criteria used for injury categorization. While it specifies that injuries were either contact or non-contact and further breaks down the analysis by injury location and timing, the specific criteria for including injuries in the dataset are not detailed. This lack of clarity may hinder the evaluation of the validity and reliability of the findings.
Response: We thank the reviewer for their valuable remark. This issue has been addressed in the Methods section under the inclusion criteria.

Comment: Inconsistent Data Presentation:
Some data are presented as means with standard deviations while others are presented as medians with interquartile ranges, and the rationale for choosing these methods is not explained. For example, the choice of using the median for playing time should be justified, as the standard deviation is used for other continuous variables. The inconsistency in data presentation could affect the interpretability and comparability of the results.
Response: The mean and standard deviation are used when the distribution of data is approximately symmetrical. In contrast, the median and interquartile range are employed for skewed distributions, such as playing time, to better represent central tendency and variability. This approach ensures that the most appropriate statistical measures are used, enhancing the interpretability of the results.

Comment: Absence of Statistical Power Analysis:
The results section lacks information on statistical power analysis, which is essential to determine whether the sample size was adequate to detect significant differences. There is no mention of how the sample size was determined or justified, which could raise concerns about the validity of the statistical comparisons made.
Response: We acknowledge the reviewer's comment regarding the absence of a statistical power analysis. Due to the nature of the study, which analyzed all available injury data from the 2021 AFCON, conducting a formal power analysis was not feasible. The study sample reflects the entire population of players and matches from the tournament, providing a comprehensive dataset. While this limits our ability to perform a prospective power calculation, we believe that analyzing the complete dataset ensures that the study captures all relevant injury patterns and associations.

Comment: Potential Bias in Injury Reporting:
The results indicate that injuries were recorded and analyzed, but there is no discussion of potential biases in injury reporting. For example, whether all injuries were uniformly reported and categorized, or if there was any observer bias in the injury assessment process, is not addressed.
Response: A section has been added to address potential biases, such as selection bias in video-based injury analysis, and how these were mitigated.

Comment: Limited Information on Contextual Factors:
Factors such as weather conditions, listed as temperature and humidity, are mentioned but not thoroughly analyzed in relation to injury incidence. The impact of these variables should be examined more comprehensively to understand their effect on injury rates. Additionally, there is a lack of analysis regarding confounding factors such as player fatigue or previous injuries.
Response: Weather conditions (temperature and humidity) have been analyzed, we haven’t find a relationship with injury incidence. We acknowledge the lack of analysis regarding confounding factors such as player fatigue or previous injuries

Comment: Inadequate Analysis of Injury Mechanisms:
While the results provide a general breakdown of injury mechanisms (contact vs. non-contact) and their occurrence by match time, there is a lack of detailed analysis of how different mechanisms relate to specific injury types or player positions. A more detailed examination could help in understanding injury patterns more comprehensively.
Response: The analysis of injury mechanisms has been expanded to explore how different player positions and match contexts influence injury patterns.

Comment: Inadequate Analysis of Injury Impact:
Although the results show variations in injury rates by match round and time, there is limited analysis of how these injuries affected player performance and match outcomes. The study does not explore how injuries impacted player availability or team performance, which could provide valuable insights into the broader implications of the findings.
Response: As suggested, we included a discussion on how injuries impacted player availability and potential performance in subsequent matches.

Comment: One of the main shortcomings is the lack of consideration for injuries ocurring during training sessions, warm-ups, and cool-downs. This is a significant limitation, as injuries during these periods can substantially contribute to the overall injury burden. Excluding these injuries from the study may lead to an underestimation of the total incidence and severity of injuries, affecting the comprehensiveness of the findings.
Response: We acknowledge this limitation and discuss how it may underestimate the total injury burden, suggesting it as an area for future research.

Comment: Additionally, the study does not report on the severity of the injuries or the duration of recovery. This omission is critical, as understanding the severity and recovery time of injuries provides crucial information on the injury burden and the long-term impact on players' health and performance.
Response: We address this limitation, indicating the need for future studies to incorporate data on injury severity and recovery time to better understand the overall burden.

Comment: The study compares injury rates with several previous studies but does not delve deeply into the potential differences in study methodologies, such as variations in injury definitions, data collection methods, or competitive environments. These differences may introduce inconsistencies in comparative findings, making it difficult to draw definitive conclusions.
Response: A discussion has been added to compare methodologies between this study and others, including how different definitions of injury and data collection techniques may influence findings.

Comment: The video-based analysis used in the study may introduce selection bias if certain injuries were less likely to be recorded or if injuries involving some players were not reported. Dependence on video footage may also overlook injuries that occurred off-camera or were inadequately captured, affecting the accuracy of reported injury rates.
Response: As suggested, some injuries may be not recorded, this discussion is added in limitation section

Comment: While the study reports injury rates by player position, it does not explore how different playing styles or positional demands might contribute to the observed injury patterns. Understanding these factors could provide a more nuanced view of injury risks associated with different player positions.
Response: As suggested, we provide a more detailed discussion of how different playing styles and positional demands may explain variations in injury patterns across player roles.

Comment: The study highlights differences between players from different leagues (NALP vs. ALP) but does not thoroughly investigate how geographical or cultural differences in training practices might influence injury patterns. These differences could contribute to variations observed in injury mechanisms and types, but are not fully explored.
Response: we acknowledge that differences in training loads, intensity, and preparation between African and non-African league players (ALP vs. NALP) could contribute to variations in injury mechanisms, this was beyond the scope of our current analysis. However, we have added a discussion in the manuscript, noting that future research should explore how regional training practices, competition schedules, and recovery protocols may impact injury risk and mechanisms, potentially contributing to the observed differences between ALP and NALP players.

Comment: The study also does not address whether players or teams had access to specific injury prevention measures, such as strength and conditioning programs or medical interventions. The presence or absence of such measures could influence injury rates and should be considered when interpreting the results.
Response: While detailed data on prevention measures were unavailable, we recommend that future studies investigate the influence of training and medical interventions on injury rates.

Comment: Despite presenting important limitations, the study does not thoroughly address the need for future research to address these shortcomings.
Response: A section on future research is included, emphasizing the need to study injury prevention strategies, the role of training, and to include training and warm-up injury data.

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Competing Interests

No competing interests were disclosed.

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Reviewer Report

14 Views

14 Jun 2024 | for Version 1

Fouad Chiha, Universite Constantine 2, Constantine, Constantine Province, Algeria

14 Views Cite this report Responses(0)

Approved

Is the work clearly and accurately presented and does it cite the current literature?

Yes
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Training methodology –football- physical preparation- exercise physiology- monotoring..

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

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Alongside their report, reviewers assign a status to the article:

Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested

Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.

Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions

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Observed events frequencies and associated factors among soccer players during the 2021 African Cup of Nations competition: A video-based exploratory analysis

Abstract

Background

Methods

Results

Conclusion

Keywords

Revised Amendments from Version 2

Introduction

Methods

Study design

Box 1. Teams who participated in the African cup of nations-2022 competition (n=24).

Box 2. List and times (T) of the 52 matches played during the African cup of nations-2022 competition.

Study protocol

Statistical analysis

Results

Table 1. African cup of nations (2022 competition): General characteristics.

Figure 1. Distribution of observed events by mechanism and time intervals of the match.

Figure 2. Progression of observed events by match rounds.

Table 2. African cup of nations (2022 competition): Factors associated with observed events.

Table 3. Comparison between «non-African» league players (NALP) and African league (ALP) players in terms of observed events characteristics.

Discussion

Study limitations

Conclusion

Ethics and consent

Data availability statement

Underlying data

Reporting guidelines

Acknowledgments

References

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