This randomized controlled trial will evaluate the effects of a 12-week intradialytic combined exercise program, consisting of aerobic and resistance training, in patients with stage 5 chronic kidney disease receiving maintenance hemodialysis. Sarcopenia, a progressive loss of muscle mass and strength, is common in this population due to chronic disease burden and the sedentary nature of dialysis sessions. The intervention group will perform structured exercise three times per week during the first two hours of dialysis, while the control group will continue routine dialysis care without exercise.

The primary aim is to investigate whether intradialytic exercise can improve dialysis adequacy and muscle oxygenation, and reduce sarcopenia severity. Secondary objectives include evaluating changes in physical performance, muscle strength, fatigue levels, and health-related quality of life. Approximately 40 participants will be randomized into intervention and control groups. Outcomes will be assessed through clinical measurements, functional tests, and patient-reported questionnaires before and after the intervention period.

Sarcopenia is a progressive loss of skeletal muscle mass and strength, associated with physical disability, poor quality of life, and increased mortality risk. Although commonly linked to aging, sarcopenia may also develop as a secondary condition in patients with chronic kidney disease (CKD) due to malnutrition, low physical activity, or treatment-related catabolism. In individuals undergoing hemodialysis, protein catabolism, inflammation, and nutrient loss are accelerated, further contributing to sarcopenia. Prolonged dialysis sessions also enforce sedentary behavior, exacerbating physical decline.

Exercise interventions have been shown to delay sarcopenia progression, improve functional capacity, and support survival. Intradialytic exercise, performed during dialysis sessions, offers practical advantages as it is time-efficient, conducted under medical supervision, and associated with better adherence compared to exercise outside dialysis. Combined programs involving both aerobic and resistance training are particularly effective in improving dialysis adequacy, reducing fatigue, and supporting muscle maintenance.

Muscle oxygenation plays an important role in sarcopenia. Factors such as oxidative stress, mitochondrial dysfunction, and impaired circulation can reduce oxygen delivery and utilization, leading to muscle weakness and atrophy. Hemodialysis itself alters microcirculation and oxygenation, negatively affecting muscle recovery. Near-infrared spectroscopy (NIRS) enables non-invasive monitoring of muscle oxygenation and has demonstrated that exercise interventions can improve tissue oxygenation parameters.

This randomized controlled trial will investigate the effects of a 12-week intradialytic combined exercise program-including aerobic and resistance training-on dialysis adequacy, muscle oxygenation, and sarcopenia severity in patients with CKD undergoing maintenance hemodialysis. Secondary outcomes will include physical performance, fatigue, and health-related quality of life.

The study will be conducted at Kadıköy Dialife Ata Dialysis Center in Istanbul, Turkey. A total of 40 participants aged 18-65 with stage 5 CKD on maintenance hemodialysis for at least one year, and diagnosed with sarcopenia according to EWGSOP2 criteria, will be enrolled. Participants will be randomly assigned to either an exercise group or a control group.

Intervention group: Participants will receive a 12-week intradialytic combined exercise program performed three times per week during the first two hours of dialysis sessions. Aerobic training will consist of supine cycling with a portable ergometer at 45-70% of maximum heart rate, adjusted progressively and monitored with pulse oximetry and the Borg scale. Resistance training will include exercises with elastic bands and ankle weights targeting upper and lower extremities, performed as 2 sets of 8-12 repetitions with progressive load increments according to ACSM guidelines. Each session will also include a 10-minute warm-up and cool-down with stretching and breathing exercises.

Control group: Participants will receive routine hemodialysis care without structured exercise. After completion of the study, the exercise program will be offered to this group.

Safety monitoring: Exercise intensity will be individualized. Sessions will be interrupted in cases of chest pain, dizziness, hypotension, severe fatigue, or excessive perceived exertion. Continuous monitoring of heart rate, blood pressure, and oxygen saturation will be conducted.

Primary outcomes will include dialysis adequacy (Kt/V, URR) and muscle oxygenation (SmO₂) assessed by NIRS. Secondary outcomes will include handgrip strength, body composition, peripheral muscle strength, the 6-minute walk test (6MWT), the Short Physical Performance Battery (SPPB), fatigue severity, quality of life (KDQOL-36), and selected laboratory parameters.

Statistical analysis will be performed using appropriate parametric or non-parametric tests according to data distribution. Significance will be set at p < 0.05.

Inclusion Criteria:

Age between 18 and 65 years

Diagnosed with stage 5 chronic kidney disease (end-stage renal disease) according to GFR, undergoing maintenance hemodialysis for at least 1 year

Diagnosed with sarcopenia based on EWGSOP2 (2018) criteria

Able to read and write

Cooperative and able to follow instructions

Voluntary participation with written informed consent

Exclusion Criteria:

Presence of orthopedic or neurological disorders affecting mobility or exercise capacity

Uncontrolled diabetes mellitus or uncontrolled hypertension

Untreated intradialytic hypotension

Heart failure

Unstable angina

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Individual participant data (IPD) will not be shared because data sharing was not included in the informed consent process.

Participants were aware of their group assignment (exercise or routine care) due to the nature of the intervention. Neither researchers nor outcome assessors were masked.