Spinal muscular atrophy type III, (SMAIII) is a disease in the nerve cells in the spinal cord which leads to to progressive muscle weakness and atrophy. No effective treatment is available for SMA. We have previously shown that patients with muscular dystrophies improve oxidative capacity (VO2max), muscle strength and daily function by aerobic conditioning. Patients with SMAIII share many clinical features with these conditions, although the mechanism of muscle weakness is different. In this study, we investigated how patients with SMAIII respond to aerobic training.