Effects of Respiratory Muscle Training on Respiratory Function and Fatigue in Multiple Sclerosis: A Systematic Review and Meta-Analysis

OBJECTIVE: To evaluate the effects of respiratory muscle training (RMT) on respiratory function and fatigue in individuals with multiple sclerosis (MS). METHODS: In accordance with the PRISMA 2020 guidelines, a systematic search was conducted across five electronic databases (PubMed/MEDLINE, Web of Science, Cochrane Library, SPORTDiscus, Scopus) from inception through 31 August 2025. Randomized controlled trials (RCTs) and quasi-randomized controlled trials (quasi-RCTs) that enrolled adults with MS who underwent isolated RMT (inspiratory, expiratory, or combined) for a duration of ≥ 4 weeks were included. Primary outcomes included respiratory function (e.g., maximal inspiratory pressure [MIP], maximal expiratory pressure [MEP], forced expiratory volume in 1 s [FEV1], forced vital capacity [FVC]) and fatigue (evaluated using the Fatigue Severity Scale [FSS] or Modified Fatigue Impact Scale [MFIS]). Data were synthesized using random- or fixed-effects models, with results expressed as standardized mean differences (SMDs) and 95% confidence intervals (CIs). RESULTS: Fifteen RCTs, comprising a total of 433 participants, were included. Meta-analysis revealed that RMT significantly enhanced respiratory muscle strength (MEP: SMD = 0.24, 95% CI: 0.03 to 0.45, p = 0.03; MIP: SMD = 0.45, 95% CI: 0.25 to 0.65, p < 0.001) and pulmonary function (FEV1: SMD = 0.37, 95% CI: 0.17 to 0.58, p < 0.001; FVC: SMD = 0.24, 95% CI: 0.04 to 0.43, p = 0.02). Significant reductions in fatigue were observed across all subscales of the MFIS (physical: SMD = -1.00, 95% CI: -1.53 to -0.46, p < 0.001; cognitive: SMD = -0.54, 95% CI: -1.05 to -0.03, p = 0.04; psychosocial: SMD = -0.88, 95% CI: -1.41 to -0.35, p < 0.001; total: SMD = -0.98, 95% CI: -1.52 to -0.43, p < 0.001). However, no significant improvement was observed on the FSS (SMD = -0.39, 95% CI: -1.10 to 0.33, p = 0.29). CONCLUSION: RMT may serve as an effective intervention for improving respiratory muscle strength, pulmonary function, and functional fatigue in individuals with MS. Nonetheless, its effect on perceived fatigue severity appears limited. These findings support the incorporation of RMT into MS rehabilitation programs. Further robust studies with standardized training protocols are warranted to confirm its long-term benefits.