Effects of intradialytic resistance versus flexibility exercises on clinical outcomes in hemodialysis patients: a pilot randomized controlled trial

BACKGROUND: Intradialytic exercise is increasingly used in hemodialysis patients; however, the comparative effects of different exercise modalities remain unclear. This pilot randomized controlled trial aimed to evaluate the feasibility and preliminary effects of intradialytic resistance and flexibility exercises on dialysis adequacy and selected clinical and patient-reported outcomes. METHODS: In this prospective pilot randomized controlled trial, 49 patients undergoing maintenance hemodialysis were allocated to control (CG), flexibility exercise (FEG), or resistance exercise (REG) groups. Exercise sessions were performed three times per week for 40 min over 12 weeks. Primary outcomes were dialysis adequacy parameters (Kt/V and URR). Secondary outcomes, including body composition and quality of life, were considered exploratory. Group × time interactions were evaluated using linear mixed-effects and nonparametric longitudinal models; given the exploratory design and limited sample size, p < 0.10 was considered indicative of potential interaction effects. RESULTS: showed no significant within-group changes, whereas URR increased in the resistance exercise group (P = 0.017). A group × time interaction was also observed for BMI (P = 0.073), with a reduction observed only in the resistance group. For quality-of-life outcomes, interactions were detected in the general health (P = 0.056) and emotional role limitation (P = 0.043) domains, with improvements observed in the flexibility and resistance groups, respectively. CONCLUSIONS: Intradialytic resistance exercise showed a signal toward improvements in URR, BMI, and SF-36 emotional role limitations, whereas flexibility exercise showed a signal toward improvement in the SF-36 general health domain. These findings suggest potential differences between exercise modalities in psychosocial and physiological outcomes. Further studies are needed to clarify which exercise modalities may provide greater benefit for specific patient profiles. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT07390656. Registered on 5 February 2026. Retrospectively registered.