Abstract: We included one RCT that studied the effects of a six-month, home-based, combined muscle strength and recumbent cycle ergometry training program versus usual care in 14 ambulatory people with SMA. The age range of the participants was between 10 years and 48 years. The study was evaluator-blinded, but personnel and participants could not be blinded to the intervention, which placed the results at a high risk of bias. Participants performed strength training as prescribed, but 50% of the participants did not achieve the intended aerobic exercise training regimen. The trial used change in walking distance on the six-minute walk test as a measure of function; a minimal detectable change is 24.0 m. The change from baseline to six months' follow-up in the training group (9.4 m) was not detectably different from the change in the usual care group (-0.14 m) (mean difference (MD) 9.54 m, 95% confidence interval (CI) -83.04 to 102.12; N = 12). Cardiopulmonary exercise capacity, assessed by the change from baseline to six months' follow-up in peak oxygen uptake (VO2max) was similar in the training group (-0.12 mL/kg/min) and the usual care group (-1.34 mL/kg/min) (MD 1.22 mL/kg/min, 95% CI -2.16 to 4.6; N = 12). A clinically meaningful increase in VO2max is 3.5 mL/kg/min. The trial assessed function on the Hammersmith Functional Motor Scale - Expanded (HFMSE), which has a range of possible scores from 0 to 66, with an increase of 3 or more points indicating clinically meaningful improvement. The HFMSE score in the training group increased by 2 points from baseline to six months' follow-up, with no change in the usual care group (MD 2.00, 95% CI -2.06 to 6.06; N = 12). The training group showed a slight improvement in muscle strength, expressed as the manual muscle testing (MMT) total score, which ranges from 28 (weakest) to 280 (strongest). The change from baseline in MMT total score was 6.8 in the training group compared to -5.14 in the usual care group (MD 11.94, 95% CI -3.44 to 27.32; N = 12). The trial stated that training had no statistically significant effects on fatigue and quality of life. The certainty of evidence for all outcomes was very low because of study limitations and imprecision. The study did not assess the effects of physical exercise training on physical activity levels. No study-related serious adverse events or adverse events leading to withdrawal occurred, but we cannot draw wider conclusions from this very low-certainty evidence. It is uncertain whether combined strength and aerobic exercise training is beneficial or harmful in people with SMA type 3, as the quality of evidence is very low. We need well-designed and adequately powered studies using protocols that meet international standards for the development of training interventions, in order to improve our understanding of the exercise response in people with SMA type 3 and eventually develop exercise guidelines for this condition.

Plain-language summary: We included one trial that studied the effects of a six-month, home-based training program that combined exercises to increase muscle strength with aerobic exercise training (exercise that increases breathing and heart rate). The aerobic exercise training used in the trial was recumbent cycling training (seated cycling, with back support). The study included 14 people with SMA type 3, all of whom were able to walk. The participants were between 10 years and 48 years old and had SMA type 3 of mild-to-moderate severity. The nature of the intervention made it impossible to hide the treatment group from participants or personnel, which is an important limitation when measurements rely on participant assessments or effort. The included study was supported by the United States Department of Defense and the SMA Foundation. Participants performed strength training as prescribed, but only half of them completed the full aerobic exercise program. The effects of physical exercise training in people with SMA type 3 remain unclear, as the evidence is very uncertain.