Progressive resistance training in neuromuscular patients. Effects on force and surface EMG.

In a randomized clinical trial the efficacy of strength training was studied in patients with myotonic dystrophy (n = 33) and in patients with Charcot-Marie-Tooth disease (n = 29). Measurements were performed at the start and after 8, 16 and 24 weeks of progressive resistance training. Surface electromyography (SEMG) of proximal leg muscles was recorded during isometric knee extension at maximum voluntary contraction (MVC) and at 20, 40, 60 and 80% of MVC. Changes in MVC, maximum electrical activity and torque-EMG ratios (TER) were calculated. Fatigue was studied by determining the changes in endurance and in the decline of the median frequency (Fmed) of the SEMG during a sustained contraction at 80% MVC. These parameters showed no significant changes after the training in either of the diagnostic groups. Only the Charcot-Marie-Tooth training group showed a gradual significant increase in mean MVC over the whole training period (21%). After 24 weeks, the increase in mean RMS was similar (25%), but this was mainly due to a sharp rise during the first 8 weeks of training (20%). The findings indicate that the initial strength increase was due to a neural factor, while the subsequent increase was mainly due to muscle hypertrophy.