This study aims to compare the effects of concentric and eccentric full can exercises on supraspinatus muscle architecture in individuals with partial rotator cuff tears.

Rotator cuff tears are a common cause of shoulder pain and functional limitation. The supraspinatus muscle plays a key role in shoulder movement and stability, and its structure may be affected in individuals with partial tears.

Exercise-based rehabilitation is widely used in the conservative management of these conditions. The full can exercise is commonly prescribed to selectively activate the supraspinatus muscle. However, the effects of different contraction types, specifically concentric and eccentric exercises, on muscle structure and clinical outcomes are not fully understood.

In this study, participants will be randomly assigned to either a concentric or eccentric full can exercise group. Both groups will receive a standard physiotherapy program, including therapeutic ultrasound and transcutaneous electrical nerve stimulation (TENS), in addition to the assigned exercise protocol.

The intervention will last for 6 weeks, with sessions performed three times per week. Outcomes will be assessed before and after the intervention.

The primary outcome is the change in supraspinatus muscle pennation angle measured by ultrasound imaging. Secondary outcomes include muscle architecture parameters, pain intensity, range of motion, muscle strength, functional status, and kinesiophobia.

The findings of this study may help improve exercise selection in the rehabilitation of individuals with rotator cuff tears.

Study Design and Setting This study is designed as a prospective, randomized, assessor-blinded, parallel-group clinical trial. The study will be conducted at Firat University Faculty of Health Sciences, Department of Physiotherapy and Rehabilitation, and Fethi Sekin City Hospital, Department of Physical Medicine and Rehabilitation.

Participants A total of 60 individuals aged between 18 and 65 years with a diagnosis of partial supraspinatus tendon tear confirmed by ultrasound or magnetic resonance imaging will be included. Participants will be randomly allocated into two groups (n=30 per group).

Randomization and Blinding Participants will be assigned to groups using a computer-generated randomization sequence. Allocation will be concealed using sealed, opaque envelopes. Outcome assessments will be performed by a blinded assessor.

Interventions

Both groups will receive a standard physiotherapy program including:

Therapeutic ultrasound Transcutaneous electrical nerve stimulation (TENS) Standard shoulder rehabilitation exercises

The only difference between groups will be the contraction type of the full can exercise:

Concentric Group: Emphasis on the lifting phase (approximately 2 seconds), with minimal eccentric loading Eccentric Group: Emphasis on the lowering phase (approximately 4 seconds), with minimal concentric loading

All interventions will be applied 3 times per week for 6 weeks (total of 18 sessions).

Outcome Measures

Primary Outcome:

Supraspinatus muscle pennation angle measured by B-mode ultrasonography

Secondary Outcomes:

Muscle architecture parameters (fiber length, physiological cross-sectional area) Pain intensity (Visual Analog Scale) Range of motion (goniometric assessment) Muscle strength (hand-held dynamometry) Functional status (DASH, SPADI) Kinesiophobia (Tampa Scale of Kinesiophobia)

Assessments will be performed at baseline (T0) and at the end of the 6-week intervention (T1).

Sample Size and Statistical Analysis Sample size calculation was based on the primary outcome (pennation angle change), assuming an effect size of 0.70, alpha of 0.05, and power of 80%. A minimum of 26 participants per group was required; therefore, 30 participants per group will be recruited to account for potential dropouts.

Data will be analyzed using appropriate statistical methods including mixed-design ANOVA for group and time comparisons. Non-parametric tests will be used if assumptions are not met. Intention-to-treat analysis will be applied.

Ethical Considerations The study will be conducted in accordance with ethical principles for human research. Informed consent will be obtained from all participants prior to inclusion.

Inclusion Criteria:

• Aged between 18 and 65 years
• Diagnosed with partial supraspinatus tendon tear confirmed by ultrasound or magnetic resonance imaging
• Shoulder pain lasting at least 3 months
• Pain intensity ≥3 on the Visual Analog Scale (VAS)
• Willing to participate and provide informed consent

Exclusion Criteria:

• Full-thickness rotator cuff tear
• History of shoulder surgery
• Shoulder instability
• Neurological disorders
• Rheumatological diseases
• Corticosteroid injection within the last 3 months
• Inability to adhere to the exercise program

Outcome assessments will be performed by a physiotherapist who is blinded to group allocation. Participants and care providers will not be blinded due to the nature of the exercise interventions.