Sarcopenia is a geriatric syndrome characterized by age-related loss of skeletal muscle mass, strength, and physical performance, leading to increased risk of falls, functional decline, and reduced quality of life. Exercise interventions, particularly resistance training, are effective in managing sarcopenia; however, land-based exercises may be challenging for older adults due to balance impairments, joint problems, and fear of falling.

Pool-based exercise programs may offer a safe and feasible alternative, as water buoyancy reduces joint loading while providing resistance to support muscle strengthening. Despite these potential benefits, evidence regarding the effects of aquatic exercise in individuals with sarcopenia remains limited, especially in Türkiye.

This study aims to evaluate the effects of a 6-week supervised pool-based exercise program on muscle strength, muscle morphology, physical performance, mood, and quality of life in individuals aged 65 years and older with sarcopenia. Sarcopenia will be identified using the Sonographic Thigh Adjustment Ratio (STAR), based on ultrasound measurements of anterior thigh muscle thickness. In addition, appendicular skeletal muscle mass will be assessed using bioelectrical impedance analysis (ASM/height²).

Outcome measures will include ultrasound-based muscle thickness, STAR, muscle strength, functional performance tests, depressive symptoms, and health-related quality of life. Assessments will be performed at baseline, immediately after the intervention, and at 1-month follow-up.

Participants aged 65 years and older who present to the Physical Medicine and Rehabilitation outpatient clinic and volunteer to participate in the study will be screened for sarcopenia. Individuals diagnosed with definite sarcopenia according to the ISarcoPRM diagnostic algorithm will be included in the study.

The aim of the study is to evaluate the effects of a 6-week supervised pool-based exercise program on muscle strength, muscle mass, muscle morphology, physical performance, mood, and health-related quality of life.

Muscle strength will be assessed using a handgrip dynamometer and the Five Times Chair Stand Test. Muscle mass will be evaluated using bioelectrical impedance analysis (BIA), and appendicular skeletal muscle mass will be calculated. Gait speed will be assessed using the 4-meter walking test. Balance and mobility will be evaluated using the Berg Balance Scale and the Timed Up and Go (TUG) test. Physical performance will be assessed using the Short Physical Performance Battery (SPPB). Psychological status will be evaluated using the Geriatric Depression Scale, and health-related quality of life will be assessed using the SF-36 questionnaire.

In addition, anterior thigh muscle thickness will be measured using musculoskeletal ultrasound. The Sonographic Thigh Adjustment Ratio (STAR) will be calculated by dividing anterior thigh muscle thickness by body mass index, providing an ultrasound-based assessment of muscle quantity and quality.

All participants will undergo a supervised pool-based exercise program for 6 weeks. The exercise program will be designed to improve muscle strength, balance, and functional performance.

All outcome measures will be evaluated at three time points: before the intervention (baseline), immediately after completion of the 6-week exercise program, and at 1 month following the end of the intervention.

Inclusion Criteria:

1. Age ≥65 years
2. Diagnosis of "definite sarcopenia" according to the ISarcoPRM diagnostic algorithm
3. Not receiving nutritional supplementation and not requiring nutritional support according to the Mini Nutritional Assessment (MNA)
4. Sufficient cognitive ability to understand and follow instructions, including study-related questions and the home exercise program
5. Voluntary participation in the study
6. Ability to ambulate independently (assistive devices such as a cane are allowed; however, fully dependent individuals will be excluded)

Exclusion Criteria:

1. Inability to complete assessment tests and questionnaires
2. Presence of severe systemic disease that may contraindicate exercise
3. Severe visual or hearing impairment
4. Presence of a cardiac pacemaker
5. Severe cardiopulmonary disease
6. Uncontrolled hypertension
7. Uncontrolled diabetes mellitus
8. Receiving nutritional supplementation
9. Severe anemia
10. Conditions contraindicating hydrotherapy, including aquaphobia (fear of water), behavioral disorders, dyspnea at rest, urinary or fecal incontinence, known chlorine allergy, open wounds, acute systemic illness, epilepsy, tracheostomy, indwelling drainage devices, and immunodeficiency

Individual participant data (IPD) will not be shared due to ethical and privacy considerations. The dataset contains sensitive personal and health-related information, and participants did not provide consent for public data sharing. Data may be made available in aggregated form upon reasonable request.