The aim of this study is to investigate the effect of post-stroke sarcopenia on prognosis and clinical outcomes in patients with ischemic stroke and to compare the effects of High Intensity Interval Training (HIIT) and Moderate Intensity Continuous Training (MCIT) exercise programs on muscle mass, as well as on functional capacity, quality of life, and clinical outcomes.

Sarcopenia is a skeletal muscle disease characterized by progressive and generalized loss of muscle mass, muscle strength, and physical performance, and is associated with an increased risk of falls, fractures, functional dependency, and mortality. Although aging is one of the most important causes of sarcopenia, factors such as acute and chronic diseases, physical inactivity, inflammation, and malnutrition also play a critical role in its development.

Stroke is one of the leading causes of mortality and long-term disability worldwide, and muscle loss occurring in the post-stroke period negatively affects the functional recovery process of patients. The loss of muscle mass and muscle strength that develops after stroke is not limited to the paretic extremity; significant muscle atrophy can also be observed on the non-paretic side. This condition is defined in the literature as "stroke-related sarcopenia".

Stroke-related sarcopenia arises through multifactorial mechanisms such as changes in muscle fiber type, motor unit loss, decreased neuromuscular activation, increased inflammatory response, and physical inactivity. Studies have shown that there is a marked reduction in motor unit number in the early period after stroke, and that this condition is associated with loss of muscle strength. In addition, it has been reported that post-stroke sarcopenia has negative effects on activities of daily living, walking capacity, and quality of life.

Exercise is considered one of the most effective interventions for the prevention and treatment of sarcopenia. The positive effects of aerobic and resistance exercises on muscle mass and functional performance have been demonstrated in many studies. In recent years, the effects of High Intensity Interval Training (HIIT) and Moderate Intensity Continuous Training (MCIT) approaches on the cardiovascular and musculoskeletal systems have been increasingly investigated.

HIIT is an exercise model in which short periods of high-intensity exercise are alternated with low-intensity recovery periods and is notable for providing high physiological adaptation within a limited time. MCIT, on the other hand, is an exercise approach performed at a longer duration and at a constant intensity. Although both exercise methods have been reported to be safe and feasible in stroke rehabilitation, data regarding their comparative effects on post-stroke sarcopenia are limited.

In the literature, the number of randomized controlled trials evaluating changes in muscle structure during the stroke rehabilitation process using objective measurement methods such as muscle ultrasonography is quite limited. Therefore, investigating the effects of different exercise approaches applied in the post-stroke period on sarcopenia, functional capacity, and clinical outcomes is important for both clinical practice and the planning of rehabilitation programs.

This study aims to investigate the effect of sarcopenia on prognosis and clinical outcomes in patients with ischemic stroke and to compare the effects of HIIT and MCIT exercise programs on muscle mass, as well as on functional and clinical parameters.

Inclusion Criteria:

• First-ever stroke.
• Age 18 years or older.
• Diagnosis of ischemic stroke.
• Stroke duration between 1-6 months (subacute phase).
• Modified Rankin Scale score < 3.
• Mini-Mental State Examination (MMSE) score ≥ 24.
• Brunnstrom lower extremity motor stage between Stage III-V.
• Lower extremity functional capacity sufficient to allow exercise participation (able to ambulate at least with an assistive device).
• Lower extremity spasticity ≤ 2 according to the Modified Ashworth Scale.
• Independent sitting balance (able to sit unsupported for at least 30 seconds).
• Presence of sufficient voluntary active movement in the lower extremity to permit exercise application.
• Ability to communicate.
• Willingness to participate in the study and provision of written informed consent.

Exclusion Criteria:

• Presence of hemispatial neglect.
• History of recurrent stroke.
• Presence of a psychiatric disorder.
• Presence of orthopedic, neurological, or cardiopulmonary conditions that would contraindicate the planned exercise protocols.

Participants and care providers will not be blinded due to the nature of the exercise interventions. However, the outcomes assessor conducting the evaluations will be blinded to group allocation. Participants will be instructed not to disclose their assigned intervention to the assessor.