This observational case-control study will compare inspiratory muscle function and diaphragm morphology between individuals with shoulder pain and asymptomatic controls. Participants will be allocated into two groups according to the presence or absence of shoulder pain.

Inspiratory muscle strength will be assessed by measuring maximal inspiratory pressure (MIP) using standardized procedures. Diaphragm thickness will be evaluated bilaterally using ultrasound imaging at the end of inspiration (Tins) and at the end of expiration (Texp).

Pain intensity will be assessed using the Visual Analog Scale (VAS). Upper limb disability will be evaluated using the QuickDASH questionnaire, including the activities of daily living module and the optional sports module.

All outcomes will be assessed in a single evaluation session. Between-group comparisons will be performed to analyze differences in inspiratory muscle strength, diaphragm thickness, pain intensity, and upper limb disability between participants with and without shoulder pain.

Inclusion Criteria:

• Tennis player who suffered from non-specific shoulder pain
• Training at least two times per week
• Have experienced at least 1 episode of non-specific shoulder pain in the last month
• A positive result on the following diagnostic tests: Neer Test and Jobe Test

Exclusion Criteria:

• Having taken anti-inflammatories or muscle relaxants within the last 72 hours before the study
• Pregnancy
• Previous diagnosis of respiratory or neurological diseases
• Previous surgeries, fractures, and dislocations in the dominant shoulder
• Inability to follow instructions during the study
• All those for whom measuring maximum inspiratory pressure is contraindicated: unstable angina, recent myocardial infarction (within 4 weeks of the even or myocarditis, uncontrolled systemic hypertension, recent pneumothorax, post-lung biopsy surgery of less than one week, postoperative abdominal or genitourinary surgery of less than 6 months, and urinary incontinence

Adult racket sport players aged 18 to 60 years, both with and without non-specific shoulder pain, recruited from local sports clubs and university-related facilities.

At this time, it is unclear whether individual participant data (IPD) will be shared. Data sharing will depend on institutional policies, ethical approvals, participant privacy considerations, and the feasibility of preparing de-identified datasets. A final decision will be made once data collection and analysis are completed.