Abstract
To investigate whether electrically stimulated exercise training might reduce muscle fatigue in persons with multiple sclerosis (MS), the dorsiflexor muscles of six patients were trained (60 min/d, 6d/wk, 8 wks) with electrically stimulated endurance exercise (50 Hz tetanic contractions, 25% duty cycle). There was evidence of transient mus cle injury at the onset of training (reduced tetanic force, elevated ratio of inorganic phosphate/phosphocreatine in the resting muscle). There was no significant effect of the training on mean muscle fatigability. After training, four of six patients had reduced fatigue (i.e., fall in tetanic force) during nine minutes of intermittent tetanic contractions. Two subjects had increased fatigue following training. Training-induced changes in fatigability were linearly associated with changes in (1) pre-exercise twitch con traction time (r2 = 0.70), and (2) the decrease in intracellular pH during exercise (r2 = 0.88), suggesting that altered fatigability after training may be associated with changes in the intrinsic properties of the muscle. These results indicate that elec trically stimulated exercise training may benefit some patients with MS. Care must be taken in the design of the stimulation parameters, and signs of muscle injury should be monitored. Further studies are needed to elucidate the most efficacious means of improving muscle strength and resistance to fatigue using electrical stim ulation in MS. Key Words: Metabolism—Muscle injury—Magnetic resonance spec troscopy—Fatigue.—Contraction—Rehabilitation.