Effects of Intradialytic Exercise on Muscle Oxygenation and Dialysis Adequacy

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.