Frozen shoulder (FS), also known as adhesive capsulitis, is a common upper extremity condition characterized by an inflammatory contracture of the glenohumeral joint capsule. This leads to progressive restriction of both active and passive shoulder movements, particularly external rotation. ¹ The condition affects approximately 2–5% of the general population and is more prevalent in females between 40 and 60 years of age. ² While pain is typically localized to the anterior shoulder, it can radiate to the anterolateral arm and significantly impair functional activities and quality of life. ^{2, 3}

Despite substantial research, the pathophysiology of FS remains not fully understood. It is hypothesized to involve a nonspecific, chronic inflammatory response in the synovial tissue, resulting in thickening and fibrosis of the capsule, and subsequent limitation of joint movement. FS is also more frequently observed in individuals with comorbidities such as diabetes mellitus, cardiovascular disease, Parkinson’s disease, stroke, and Dupuytren’s contracture, as well as those with a history of neck or cardiac surgery, smoking, or hyperlipidemia. ⁴

The clinical presentation of FS varies with disease progression. In early, high-irritability phases, patients often report intense pain with minimal stiffness. As the condition advances, stiffness becomes the predominant symptom with reduced pain levels. ^{3, 4}

Exercise therapy is widely regarded as an effective conservative management strategy for FS. ⁵ Early-stage interventions typically include pendulum (Codman’s) exercises, wall walks, pulley-assisted movements, and shoulder wheels. As pain subsides, rehabilitation progresses to stretching, isotonic exercises, rotator cuff and scapular strengthening, and joint mobilization techniques. ⁶

Eccentric exercises, those that involve muscle lengthening under load, have been found effective in treating various musculoskeletal disorders, including subacromial impingement syndrome, lateral epicondylitis, and rotator cuff tendinopathy. ^{7– 10} These exercises generate high mechanical tension, believed to promote remodelling of connective tissues and improve neuromuscular control. ⁸ Their metabolic efficiency and ability to induce tissue adaptation have made them a subject of growing interest in rehabilitation research.

Although eccentric training has demonstrated effectiveness in upper limb disorders, its application in frozen shoulder remains underexplored. Considering the potential for improving joint range, muscular flexibility, and tendon compliance, eccentric training may serve as a valuable therapeutic strategy in FS management.

Therefore, we hypothesized that eccentric control exercises targeting the rotator cuff and shoulder musculature would improve pain, range of motion, functional disability, fear of movement (kinesiophobia), and pain self-efficacy in patients with frozen shoulder and mild to moderate disability.

The aim of this study was to investigate the effectiveness of an eccentric control exercise protocol on physical and psychosocial outcomes in this population.

The study was conducted at an outpatient department in a medical college Hospital after obtaining approval from the authors affiliated institutions. This is a single group pre-post design which included 20 patients with FS with mild-moderate disability. The clinical trial registration number for the study is CTRI/2023/01/048754. The study was conducted from December 2022 to October 2023. The inclusion criteria were age between 40 and 65 years of both the gender, diagnosed case of frozen shoulder (equal limitation of active range of motion and passive range of motion and normal X ray) with mild to moderate disability <50% reduction of external rotation when comparing opposite side, for mild disability Pain intensity was 3/10 on numerical pain rating scale, No night pain or sleeping pain, both active and passive range of motion are equally limited, but can tolerate passive overpressure at end range of motion. For moderate disability, pain was 4-6/10 on numerical pain rating scale, periodic ache while sleeping or resting, both active and passive range of motion are equally limited, can tolerate basic shoulder loading. The Exclusion criteria include FS patients with calcifying tendinitis, Greater tuberosity fracture, Necrosis of the humeral head, Rotator cuff related shoulder pain, pseudo-frozen shoulder, Neoplasm, Osteonecrosis, Cervicogenic shoulder pain, Locked dislocation, Glenohumeral osteoarthritis.

The demographic characteristics of the recruited sample are presented in Table 1. Since the demographic variables follow a normal distribution, they are expressed as mean ± SD with range.

Table 2 displays the recorded data for outcome measures at baseline, post-intervention, 3-month follow-up, and 6-month follow-up.

The effect size indices for the outcome measures SPADI, TSK, PSEQ, NPRS, SFI, Sab, SHb, and SEr were 1.48, 2.49, 0.93, 0.89, 1.93, 2.25, 2.96, and 1.15, respectively, indicating that the treatment was effective.

Figure 8 illustrates the timeline changes in patients with frozen shoulder (FS).

Figure 9 shows the timeline changes in TSK scores in patients with FS.

Figure 10 depicts the timeline changes in PSEQ scores in patients with FS.

This is the first study to evaluate the effects of eccentric control exercises in patients with frozen shoulder (FS) and mild to moderate disability, using a range of outcome measures including psychosocial parameters such as kinesiophobia and pain self-efficacy.

Previous research has shown that eccentric exercises outperform concentric exercises in improving pain, muscle strength, and function in various shoulder conditions such as subacromial impingement syndrome and rotator cuff tendinopathy. ^{18– 20} In the present study, the observed recovery in shoulder range of motion (ROM) may be attributed to an increase in sarcomere length and alterations in passive tension within the rotator cuff muscles or surrounding connective tissue structures. ²¹

Eccentric exercises have demonstrated rapid improvements in ROM, often with less energy expenditure than stretching. Unlike concentric contractions, which involve muscle shortening, eccentric contractions occur while the muscle lengthens under tension. This method of training is more metabolically efficient, as it requires less energy to produce the same force. ²² In addition to musculoskeletal benefits, eccentric exercises are known to enhance insulin sensitivity, promote muscle regeneration, improve lipid profiles, increase cortical excitability, and boost cardiorespiratory fitness. ¹⁷ Owing to these systemic effects, eccentric exercises have been utilized in managing conditions such as type 2 diabetes, sarcopenia, and cardiorespiratory disorders. ¹⁷

The primary goals of FS treatment include increasing both active and passive ROM, reducing pain, and improving shoulder function. ²³ In our study, shoulder flexion, abduction, hand-behind-back (HBB) reach, and external rotation all showed notable improvements following the intervention. Importantly, our protocol involved a longer eccentric contraction duration of 10–15 seconds, which contrasts with earlier studies that adopted shorter durations. ^{16, 17}

A systematic review concluded that eccentric training is more effective than concentric training for enhancing muscle mass in healthy individuals. ¹⁸ Additionally, individuals with subacromial pain syndrome demonstrated significant functional gains following eccentric exercise interventions. ¹⁶ Another study suggested that eccentric control exercises may be a key component of rehabilitation, particularly in female patients with FS. ^{6, 18} Based on these insights, we hypothesized that the improvements observed in our study may be due to mechanical changes such as reorganization of collagen fibers in the joint capsule and remodelling of adhered tissue. ²⁴ Furthermore, increased synovial fluid circulation may have contributed to capsular tissue softening and increased joint mobilit. ²⁵

Strength of the study: The internal validity of this study is strengthened by the standardized protocol, consistent outcome assessment tools, and blinded assessment of outcome measures. The study has several limitations that must be acknowledged. As a single-group pre-post design, it is vulnerable to threats such as history, maturation, and regression to the mean, which may confound the observed effects. The significant improvements seen across various timelines are encouraging, but without a control group, causal inferences should be made cautiously.

The external validity, or generalizability, is limited due to the small sample size (n=20), and single-centre design. While the results may be applicable to similar clinical populations in controlled settings, their extrapolation to broader populations (e.g., patients with severe FS, different age groups, or other comorbidities) should be done with caution.

Suggestions for future research

Future studies should consider using randomized controlled trials with larger and more diverse samples to compare eccentric exercises with other standard or emerging physiotherapy interventions. Inclusion of a placebo or active control group would help establish causal relationships. Additionally, further investigation into the neurophysiological and biomechanical mechanisms underlying the effects of eccentric loading in FS may enhance understanding and inform protocol optimization. It would also be beneficial to explore the long-term adherence to home-based eccentric programs and their impact on sustained functional recovery.

Eccentric control exercises led to significant improvements in pain, functional disability, range of motion (including flexion, abduction, hand-behind-back, and external rotation), pain self-efficacy, kinesiophobia, and patient satisfaction in individuals with frozen shoulder and mild to moderate disability.