Neuromuscular function in limb girdle dystrophy.

The contractile properties of ankle dorsiflexor and plantarflexor muscles in 20 patients with limb girdle muscular dystrophy have been compared with those in matched controls. Twitch and voluntary torques were significantly smaller in the patient population and in nine patients it was impossible to record a twitch from tibialis anterior, a dorsiflexor muscle studied in detail. The disease process evidently ran a more rapid course in tibialis anterior than in plantarflexor muscles and this susceptibility was related to some aspect of the muscle other than its fibre type composition. Surviving fibres in dorsiflexor and plantarflexor muscles did not reveal evidence of excitation-contraction uncoupling; they exhibited normal post-activation potentiation and fatigue properties. Some patients were initially incapable of exciting their motor units maximally during voluntary contractions. A finding of possible pathogenetic significance was that one patient, with prominent calves, developed exceptionally large voluntary torque in his plantarflexor muscles.