. Aerobic exercise aims to improve aerobic capacity.

. To summarize the evidence on the efficacy of aerobic exercise on aerobic capacity in slowly progressive neuromuscular diseases (NMDs).

. We searched the electronic databases MEDLINE, EMBASE, SPORTDiscus and Web of Science Conference Proceedings Index for articles published up to June 17, 2021, selecting randomized controlled trials that included adults with slowly progressive NMDs and compared aerobic exercise to no aerobic exercise. The primary outcome was peak oxygen uptake (VO₂peak) directly post-intervention. Secondary outcomes included other peak test parameters, submaximal test parameters, long-term outcomes ≥8 weeks post-intervention, adherence and adverse events. Meta-analyses were performed for the primary outcome and for secondary outcomes when reported in more than 2 studies. Risk of bias was assessed with the Cochrane Risk of Bias tool and quality of evidence according to GRADE.

. Nine studies were included (195 participants with 8 different NMDs). Eight studies were rated at high risk of bias and 1 study was rated at some concerns. Duration of exercise programs ranged from 6 to 26 weeks, with 3 weekly training sessions of 20 to 40 min, based on maximal capacity. Meta-analyses revealed short-term moderate beneficial effects of aerobic exercise on VO₂peak (standardized mean difference [SMD] 0.55, 95% CI 0.23; 0.86) and peak workload (SMD 0.61, 95% CI 0.24; 0.99). Long-term effects were not assessed. Most training sessions (83-97%) were completed, but time spent in target intensity zones was not reported. Included studies lacked detailed adverse event reporting.

. There is low-quality evidence that aerobic exercise is safe and leads to moderate improvement of aerobic capacity directly post-intervention in slowly progressive NMDs, but the long-term efficacy remains unclear. Detailed information about the time spent in target intensity zones and adverse events is lacking.

: CRD42020200083