Assessment of cardiorespiratory fitness among medical students: a prospective study [version 1; peer review: 2 approved with reservations]

Background: Physical activity and fitness level of fitness decline mostly between adolescence and early adulthood. This leads to risks of non-communicable diseases in the future. Medical students, assumed to have an extensive understanding of physical exercise and its benefits, are less active than they were before attending graduate school. This study aimed to assess changes in physical fitness and physical activity of students over-time. Methods: This was a prospective study undertaken at Basic Science Complex of Kathmandu Medical College Teaching Hospital in Nepal. In total, 72 medical students were put through a modified Harvard step test during their first year and then three years later during their third year at medical school. Maximum aerobic capacity (VO 2 max) was calculated subsequently by plotting the average pulse rate on the Astrand-Rhyming Nomogram. Results: The mean value of relative maximum aerobic capacity (VO 2 max) decreased from first year to the third year. When the mean values of body mass index and relative maximum aerobic capacity were compared between first year and third year, the difference was found to be statistically significant (p-value=0.000). The physical


Introduction
Non-communicable diseases (NCDs) are the leading cause of death worldwide and are emerging as a global health threat.NCDs account for 71% of all deaths globally, out of which 77% of death are in middle and low income countries according to data extracted from WHO website on NCDs which was last updated on 13 th April, 2021. 1 Physical fitness is considered one of the most important health markers, as well as a predictor of morbidity and mortality of various noncommunicable diseases. 2About one and a half million deaths due to NCDs worldwide annually can be attributed to insufficient physical activity. 1ysical fitness is defined as a set of attributes or characteristics individuals have or achieve, that relates to their ability to perform physical activity 3 while physical activity is defined as any bodily movement produced by skeletal muscles that result in energy expenditure. 4A higher level of physical fitness is credited with lower rates of cardiovascular disease and also has positive effects on depression, anxiety, mood status, and self-esteem. 2,5However, the physical activity and fitness level of youth is steadily declining with more than one-third of the population being unfit -which appears to occur during adolescence and early adulthood. 6A recent study also showed a marked decline during high school and university years. 7College life is a period during which individuals have to struggle with academic workload, lack of free time -often picking up habits like smoking and lack of balanced diet posing a barrier to the adoption of healthy practices. 8In spite of this, it is presumed that medical students have substantial knowledge about physical activity and its benefits.However, research has shown that more than half of the clinicians and medical students perform less physical activity, as compared with their levels of activity undertaken prior to graduate training. 7 health care professionals, medical students will influence their patient's attitude toward maintaining optimal physical fitness and advocating good health physical exercise.For better productivity, students should be healthy and have good physical fitness. 9Therefore, there is a need for students to measure and analyze their physical fitness for their benefit.There are few studies regarding physical fitness among medical students in Nepal.Hence, the present study emphasizes assessing physical fitness among young medical students in a tertiary care hospital with the help of a heart rate which is measured in terms of maximum aerobic capacity (VO 2 max).VO 2 max has been considered by the World Health Organization as the single best indicator of cardiorespiratory fitness. 10Cardiorespiratory fitness is the overall capacity of the cardiovascular and respiratory systems and the ability to carry out prolonged strenuous exercise.It is one of the most frequently cited measurable components of physical fitness; other components include muscular endurance, muscular strength, body composition, and flexibility. 3VO 2 max is the maximal oxygen consumption attained during a graded maximal exercise to voluntary exhaustion. 11,12Direct measurement of VO 2 max is the standard index of cardiorespiratory fitness, although the use of indirect measurement of VO 2 max is considered suitable for epidemiological studies. 13 the present study, a step test has been used for measuring the VO 2 max of students as it is considered to be a practical field test for assessing individual aerobic fitness. 14This prospective study aimed to assess changes in physical fitness and physical activity of students in their first year at medical school followed up in the third year to assess the changes.

Study design
This was a prospective study conducted in Basic Science Complex of Kathmandu Medical College Teaching Hospital, Duwakot in Nepal between January 2017 and January 2020.It included apparently healthy male and female medical students in their first year willing to participate voluntarily.The same participants were followed up during their third year and underwent the same test.Participants having any acute or chronic illness, locomotive and musculoskeletal disability, and those taking regular medications were not included in this study.Convenience sampling was used to collect data, which included all 150 medical students in the class.The students were briefed in the class about the project and were asked for voluntary consent, and 72 of the participants agreed to take part in the research.Since this was a convenient sampling we were not able to address potential bias in the study.The limitation of this design is that it lacks generalizability and may not be representative of the sample population.

Statistical methods
The data was collected, compiled and analyzed using Statistical Package for the Social Sciences (SPSS) software version 20.Analysis was done using descriptive statistics like frequency, percentage, mean, standard deviation, and inferential statistics like students t-test and Pearson correlation analysis.

Ethical considerations
Ethical clearance was obtained from the Institutional Review Committee of Kathmandu Medical College (approval reference number: 30122016, approved granted on 30 th December 2016) prior to data collection.Informed written consent with details of ethical issues (confidentiality, anonymity, and beneficence) was obtained from all the participants of this study.All procedures were conducted in accordance with the principles of the Declaration of Helsinki.Participants received no monetary compensation.

Procedure
Prior explanation about the aim and purpose of the study, test procedure, method of testing, and instructions on how to perform the test were given.Detailed history of each participant was taken which included any history of hypertension, diabetes, asthma or any chronic illness along with any medications being taken.They were also assessed for any physical disabilities and their anthropometric measurements like weight, height, and body mass index were noted.Weight was measured with CAMRY digital weighing scale Model no EB9374.Subsequently, the students were put through a modified Harvard Step Test.The step test was conducted in a closed room during evenings at the hostel premises for the convenience of the students.The step test was undertaken by the authors themselves with proper instructions.The process undertaken to conduct the Harvard step Test was replicated completely during the follow-up session with no difference in the procedure.
The Harvard Step Test is a submaximal step test used as an indirect predictor of VO 2 max.Submaximal step tests are those tests that measure the VO 2 max without the test protocols reaching the maximum of their cardiovascular and respiratory system performance.The original Harvard Step Test was developed for taller people of western countries by Brouha et al  (1943) during World War II which consisted of a big step with a height of 20 inches. 15However, this test is not applicable to relatively shorter people of Nepal.The application of the original Harvard Step Test was also found to be unsatisfactory in the Indian population because of the step height of 20 inches. 16Therefore, in the modified Harvard Step Test, a shorter step height of 16 inches has been used.
After familiarizing the participants with the Harvard Step Test, resting pulse rate was noted.The participants were then asked to step up and down the step.A metronome was used to maintain the rhythm.On the count of one, the participants would keep one foot on the bench followed by the other; on the count of two he/she would put the first foot off the bench followed by the other.The participants were asked to step up and down 20 times per minute according to the metronome for five minutes or until exhaustion. 17Exhaustion is defined as the point when the participant can no longer maintain the stepping rate for 15 seconds.The time was noted with the help of a stopwatch.At the end of the test, the participants were asked to sit on a chair and the pulse was measured.The pulse was recorded during one to one and half minute, two to two and half minute, three to three and half minute interval immediately after the test.This is called recovery pulse. 16VO 2 max was then calculated by plotting the average pulse rate on the Astrand-Rhyming Nomogram. 18ysical fitness was calculated by the formula: Fitness Index long form ð Þ¼ 100 Â test duration in seconds ð Þ divided by 2 Â sum of heart beats in the recovery periods ð Þ :

Results
A total of 150 participants were approached to include in the study.However, only 72 participants met the inclusion criteria after undergoing examination for eligibility and giving consent and were hence included in the study. 33Among them, 49 were men and 23 were women.In the follow-up session all 72 participants were again assessed for any new disabilities, illness or intake of medications and all were deemed eligible and participated in the study.No participants were lost to follow-up.Majority of the participants were adolescents within the age range of 18-22 years.The mean AE standard deviation (SD) of BMI, physical fitness index (PFI) and relative VO 2 max is shown in Table 1.When the mean values of BMI and Relative VO 2 max was compared between the first year and the third year, the difference was found to be statistically significant with P value of 0.000.However, the difference in mean value of PFI was not found to be statistically significant with P value of 0.610 (Table 1).
Majority of the participants had a normal BMI.Number of participants who were underweight decreased from 15 to 9 whereas the number of participants in the overweight and obese groups increased (Table 2).
Most of the students had excellent PFI scores, 55 students in the first year and 56 in the third year.Only 5 students had poor PFI in the first year and 6 had poor PFI in the third year (Table 3).
Physical fitness Index mean value was similar, with 78.87AE18.86 and 79.43AE19.99 in the first and the third year respectively.It was found that there was no significant difference in the mean values of Physical fitness index in the first and the third year (Table 4).This table shows the comparison of categories of BMI with relative Vo2 max in the first year.The majority of the participants fall under the normal BMI category and had a relative v02 max of 37.92 ml/kg/min.Only 16 participants fall under the overweight and obese category of BMI and had a comparatively lower relative Vo2 max of 36.19 ml/kg/min and 34.09 ml/kg/min respectively (Table 5).
Through this table we can see that the mean relative V0 2 max has decreased from the first year to the third year.The mean relative VO 2 max was 37.46AE7.67ml/kg/min in the first year vs 34.95AE7.7 ml/kg/min in the third year.In the table we can also see that a higher change in VO 2 max was seen in the male population with 3.1ml/kg/min difference in the first year and the third year (Table 6).
In the first year, the correlation coefficient between PFI and relative VO 2 max was 0.594 with a P value of 0.000 which was statistically significant.Students with a higher VO 2 max also had high PFI (Table 7).
In the third year, the correlation coefficient between Physical Fitness Index and relative VO 2 max was found to be 0.475 with a P value of 0.000.The correlation was found to be statistically significant (Table 8).
The correlation coefficient between BMI and relative VO 2 max in the first year was found to be -0.123 with a P value of 0.302.The correlation was not found to be statistically significant (Table 9).The correlation coefficient between BMI and Relative VO 2 max in third year was found to be -0.238 with a P value of 0.045.The correlation was found to be inverse and statistically significant (Table 10).

Discussion
This study is a prospective study conducted once the students entered medical school during their first year.A follow-up data collection was done during their third year after having spent three years in medical school with no intervention in between.Various parameters indicating cardiorespiratory fitness were compared as the participants progressed through medical school.Amongst those parameters, VO 2 max was taken as the best indicator of cardiorespiratory fitness.

Body mass index Body mass index comparison in medical school
We measured the BMI of medical students when they first entered medical school and compared it with their BMI three years later.In the first year, 13.8% of the students were overweight and 8.3% of the students were obese.Subsequently, in the third year, 22.2% of them were found to be overweight and 9.72% of them were obese.The mean BMI in the first year and third year were 21.07AE3.02and 21.63AE3.05,respectively.The comparison of the baseline BMI and subsequent BMI showed a statistically significant increase.

BMI of medical students of Nepal in previous research
A study conducted in 2005 among students of third-year medical school in Nepal 19 showed only 1% and 2% of males and females to be overweight.However, a study conducted in 2017 at the Institute of Medicine found 32.5% of students to be overweight and 11.4% to be obese. 20However, a prospective study comparing BMI of medical students in Nepal was not found.

BMI changes in students of university program
A prospective study monitoring weight gain of students as they entered the university as a freshman and during their sophomore years was done in the United States. 21The study which was conducted in two universities, showed an increase of 3.1% and 15.6% in overweight/obesity rates from baseline to sophomore year, respectively.This study also supports the theory that getting into a university for a graduate degree may affect fitness level.

Prevalence of obesity in Nepal
According to the STEPS survey in 2019 of Nepal, 20% of adults were overweight and 4.3% were obese. 22Comparing this with our data on youths (18-22 years) which is a subset of the population taken in the STEPS survey we can see that practices leading to overweight and obesity begin from this age range in the youth itself.This study helps us show that targeting interventions in youth during their academic ventures can help reduce the overall overweight and obesity burden of Nepal.

Cardiorespiratory fitness Relative VO 2 max change in medical school
A relative VO 2 max is considered the strongest indicator of cardiorespiratory fitness.We found that the baseline mean relative VO 2 max was found to be 37.46AE7.68ml/kg/min.In the final data collection, the mean relative VO 2 max was 34.95AE7.72ml/kg/min.Although the mean VO 2 max was found to be in the average range of non-athletes which is 35-40ml/kg/min for males and 27-31ml/kg/min, 23 it showed a statistically significant decrease from the first year to the third year.This study indicates that the cardiorespiratory fitness of the students decreased after being enrolled in medical studies.During the transition into college years, various factors come into play; academic pressure, changes in family and peer social support and risk-taking behaviors. 24Studies have also found that academic stress that students face in medical school brings about a decrease in exercise, poor nutrition and increased drug use 25 ; all these combined plays a critical role in declining fitness.Moreover, there is evidence suggesting that youths who attend college are prone to have a greater weight gain than those who do not which also impacts fitness. 26The findings in these studies support our findings suggesting that college students experience a decline in fitness as they progress through school.

VO 2 max of medical students in Nepal in previous research
A 2008 study done at Nepal Medical College in medical students who did not smoke showed a VO 2 max of 54.32ml/kg/ min and 44.88 ml/kg/min in men and women, respectively. 27Similarly, a study done to assess cardiorespiratory fitness in 2013 at Kathmandu Medical College showed a VO 2 max of 48.8 and 37.3 ml/kg/min in boys and girls. 28These data showed considerably good cardiorespiratory fitness at a point of time.However, since the studies were cross-sectional studies we cannot predict the progression of cardiorespiratory fitness throughout medical school.A previous study done in a similar age group of Nepalese youth also showed a VO 2 max of 48.30 ml/kg/min. 29In regards to the previous studies where absolute VO 2 max is calculated, our study calculated relative VO 2 max, the difference being that the absolute VO 2 max is the total amount of oxygen consumed by the body irrespective of the person's age, gender, mass while relative VO 2 max is the value corrected for mass.This change was essential as the relative VO 2 max helped us compare individuals and their own previous VO 2 max.For example, a heavier person burns more oxygen during rest showing high absolute VO 2 max when in reality VO 2 max corrected for the mass may show a lower value.This fact helps us understand that absolute VO 2 max values are not ideal for comparison since their weight is a variable parameter.Also, we were able to do a prospective study which helped us compare the change in VO 2 max as the students progressed through medical school.
Compared to these studies we can see that in the current scenario the VO 2 max of Nepalese youth has significantly decreased portraying the increasing trend of a sedentary lifestyle and increased risk of non-communicable diseases.The nationwide STEP 2019 survey 22 has also shown the increasing trend of obesity and increased risk of non-communicable disease in Nepal in the current scenario to support this theory.

VO 2 max of students in other university programs
A cross-sectional study conducted in the department of physiology of Maharishi Markandweshwar Institute of Medical Sciences and Research, Mullana found that VO 2 max for men was 45.66AE8.9ml/kg/min and for women was 37.85AE4.3ml/kg/min.This study is also a cross-sectional study unlike ours and is unable to predict changes in the VO 2 max levels.From the study, it was concluded that their subjects fitted in the category 'fair' on cardiorespiratory fitness scale, which could be because of the decreased physical activity, unhealthy lifestyle behaviors as are established during the years of gaining education, which may influence adult behavior and health status. 30other study compared the VO 2 max levels of male students of one university with the other and also, female students of one university with the other.Maximum oxygen consumption of male students fall in the category 'good', according to the criteria of Cooper's oxygen consumption, for the Romanian students, the value is 50.9, while for the Serbian students, the value is 46.1 ml/min/kg.The maximal oxygen consumption of female Romanian students was 39.6, and of female Serbian students was 34 ml/min/kg, according to Cooper, it falls in the category 'average'. 31This research showed that the maximum oxygen consumption of students across different universities is comparable, however, they fail to elucidate factors that can influence VO 2 max levels.

Relative VO 2 max correlation with BMI
In our study, we have found that in the third year, the relative VO 2 max of students decreased with increase in BMI.
A study conducted in 2020 also revealed similar results 32 .It is also seen that a larger body mass and a high degree of correlation between body mass and relative VO 2 max indicators are characteristics of mesomorphic and endomorphicmesomorphic somatotypes.Whereas, smaller body mass and a lower degree of correlation between body mass and relative VO2 max indicator are characteristics of ectomorph and balanced somatotypes. 32This shows that different body types have a different characteristic association between relative VO 2 max and Body mass index.

Conclusion
Our study being a prospective study covered the gap in data that arose from cross-sectional studies about fitness levels in students.This study was able to provide data about medical students' physical fitness which may contribute to the burden of non-communicable disease in the future.The significant data showing changes from the first year to the third year of medical school represents lack and/or decrease of physical activity during the time period in the school.This highlights a major gap in the curriculum i.e focus on the physical fitness of the students.The academic coursework should include and proactively focus on the physical activity of the students and promote them to adopt a healthier lifestyle as a part of their daily routine.If implemented this could significantly decrease the burden of non-communicable diseases in the future.

Data availability
Harvard Dataverse: Assessment of Cardiorespiratory fitness among medical students: A prospective study.https://doi.org/10.7910/DVN/HNZKHI. 33ta are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).

INTRODUCTION
Despite being well written, the introduction does not provide enough information based on the level of cardiorespiratory fitness in university students and its consequences for this population.In order to contribute to the study, the authors could use the study by (Jalene et al., 2019 1 ) or the study of (Singh et al., 2023 2 ).

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The authors cite that "A recent study also showed a marked decline during high school and university years, however reference 7 is from 2011 (12 years ago).Could you insert a newer reference?

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The authors describe at the end that "In the present study, a step test has been used for measuring the VO 2 max of students as it is considered to be a practical field test for assessing individual aerobic fitness.I believe it is necessary to say that other tests can be used to assess this capacity, therefore, better justify the use of this test.

Study design
The paragraph "The limitation of this design is that it lacks generalizability and may not be ○ representative of the sample population" refers to the limitation of the study, I believe it would be better at the end of the discussion.

Statistical methods
Was the analysis of normality of data distribution performed?Both the t-test and Pearson's correlation require that the data have a normal distribution for their use.Also include the degree of significance used (e.g.p < 0.05 or 5%).

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Place this item at the end of Methods.

Ethical considerations
Insert this item right after Study design ○

RESULTS
Was any analysis of the level of physical fitness, for example the IPAQ, carried out at the beginning of the assessments?This data is very important to analyze each student individually.Thus, it will be possible to establish the baseline level for the first analysis.If no initial physical fitness assessment was performed, this should also be considered as a limitation of the study.

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The first paragraph should be in the methodology as a description of the sample.
○ I suggest that the data from tables 1, 2 and 3 are in a single table.

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Why was the data analyzed with men and women together?It is known that men and women have different characteristics, mainly related to the hormone.... men are modulated by testosterone (greater fat free mass gain) while women by progesterone (greater fat accumulation).Were analyzes performed separately by gender?Were the results the same?I believe justification is needed for these joint analyses.

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It would be interesting, in the tables or in the text, to put the values in %, as it would facilitate the comparison and analysis of the results.

DISCUSSION
The discussion is long, could be more specific and discuss the results without the need for threads.

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In addition, it is necessary to add the limitations of the study, for example, the low number of participants, in addition to the items mentioned above.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, however I have significant reservations, as outlined above.

Methods
Generally well written and procedures well described.1.
This study took place between January 2017 and January 2020.It may be necessary to let readers appreciate how a student in 1 st year of study in 2017 would only be a 3 rd year in 2020 (and not a 4 th year).

2.
The sampling technique looks more like a census and not convenience.All students who gave consent were sampled.

Results
Normally, females and males perform physical activities differently and, further, have differences in the various physiological parameters -for example, their VO2max values are graded differently.It is unclear why their data was pooled together for analysis. 1.
There are a lot of repetitions of data (tables and prose).This should be revised.

2.
BMI categorizations and physical fitness index categories should be defined for readers.For example, what does "very good PFI" mean?What does "underweight" mean?

3.
Table 4 refers to PFI between 1 st and 3 rd year yet the table data is for 1 st and 2 nd year.4.
Tables 5 and 6 have VO2max pooled for males and females.This should be disaggregated for sex and age as physiologically expected.

5.
There are too many tables!10.This makes the work a little untidy.They could be reduced to a maximum of 4 or 5 without losing the information they carry.

Discussion
The opening statement "This study is a prospective study conducted once the students entered medical school during their first year" needs revision.It is not sound.

1.
Authors state "A follow-up data collection was done during their third year after having spent three years in medical school with no intervention in between."If they have spent 3 years since joining 1 st year, then they are in 4 th year and not 3. No? 2.
The discussion section has a lot of results.This should be revised.Discussions should explain the findings and the physiologic mechanisms involved, and place the current findings in perspective given other studies.

3.
Authors compare their cardiorespiratory fitness findings with those from literature that are already disaggregated per sex.Theirs are not.It would be interesting to see if there is a drop in both sexes or how this compares.

Conclusion
Some conclusions are not derived from the current work.For example, we do not know that the curriculum lacks in physical activity scheduled time and etc. 1.

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?Partly Are all the source data underlying the results available to ensure full reproducibility?No

Are the conclusions drawn adequately supported by the results? Partly
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Medical physiology/exercise and sports medicine 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, however I have significant reservations, as outlined above.
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Table 1 .
Mean values of body mass index, physical fitness index and relative VO 2 max.

Table 2 .
Body mass index categorization.

Table 4 .
Physical fitness index mean value comparison among the students in first year and third year.

Table 3 .
Physical fitness index (PFI) score categorization and frequency.

Table 5 .
Comparison of relative VO 2 max in the first year with body mass index (BMI).

Table 6 .
Comparison of relative VO 2 max in the first year and the third year.

Table 7 .
Correlation between physical fitness index and relative VO 2 max in the first year.

Table 8 .
Correlation between relative VO 2 max and physical fitness index in the third year.

Table 9 .
Correlation between body mass index and relative VO 2 max in first year.

Table 10 .
Correlation between body mass index and relative VO 2 max in third year.

the study design appropriate and is the work technically sound? Yes Are sufficient details of methods and analysis provided to allow replication by others? Yes If applicable, is the statistical analysis and its interpretation appropriate? Partly Are all the source data underlying the results available to ensure full reproducibility? Yes Are the conclusions drawn adequately supported by the results? Yes
○ Partly Is Competing Interests: No competing interests were disclosed.Reviewer Expertise: Experience in Physical Activity and Health, Exercise Physiology and Sports Training with emphasis on Growth and Development, Body Composition and Bone Geometry.