A 12-week moderate resistance exercise program was performed by 27 patients with slowly progressive neuromuscular diseases (NMD) and 14 control subjects (CTL) in order to determine safety and efficacy of a strengthening program. A 3-day per week submaximal regimen of home exercise using ankle and wrist weights and hand grip exerciser was prescribed. One side of the body was randomly chosen for exercise. Subjects were tested for maximal isokinetic and isometric strength at baseline and after weeks 4 and 12 of the training protocol, and the prescribed amount of work was gradually increased throughout the program. Both the NMD and CTL groups demonstrated significant (p < .05) increases in most strength measures. Both groups responded similarly to the exercise program, and strength gains did not significantly differ between the exercised and nonexercised limbs in either group. This study provides evidence that a 12-week submaximal strength training program is practical and safe in slowly progressive NMD and produces moderate improvement in measured strength.