Aerobic Training Improves Oxidative Capacity, But Not Function in Spinal Muscular Atrophy III

Spinal muscular atrophy type III, (SMAIII) is a recessively inherited disease in the lower motor neuron in the anterior horn of spinal cord leading to to progressive muscle weakness and atrophy. Currently there is no effective treatment 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.

6 patients and 9 healthy age- and sex-matched controls completed a 12 weeks training program. Subjects performed a total of 42 training session of 30 min on a stationary cycle ergometer at home. The work intensity was moderate and set to match a target heart rate.

VO2max was measured during a incremental exercise test using indirect calorimetry before and after the training period. Functional tests adressing patients walking and stair climbing abilities, were performed before and after the training period. Changes in activities of daily living was adressed in a standardized questionnaire after the training period.

Training induced an increase without inducing muscle damage. There were no changes in patients' functional capacities. However, training-induced fatigue was a major complaint in all patients, and caused one patient to drop out, increased the need for sleep in three patients and two had to modify the training program.

The fatigue limits the use of this therapy. The training-induced fatigue, which is not encountered in muscle diseases, warrants investigations into alternative training methods to improve quality of life in patients with SMAIII.