- An electrophysiological study has been made of extensor digitorum brevis muscles in 19 boys with Duchenne dystrophy. The isometric twitches of the dystrophic muscles developed less tension and were usually slower than those in controls. Impulse conduction velocity appeared to be reduced in distal regions of nerve axons but was normal proximally. The most interesting finding was a reduction in the number of functioning units in all but one of the patients. The sizes of the surviving units suggested that the results could be explained more easily in terms of a neurogenic process than a primary myopathic one.