Pattern of recruiting human motor units in neuropathies and motor neurone disease.

The pattern of recruiting human motor units in the first dorsal interosseous muscle of the hand has been studied in 31 patients with ulnar neuropathies and motor neurone disease. Two years after surgical repair of an unilateral complete severance of the ulnar nerve, the twitch tensions increased to normal size. However, the normal orderly pattern of recruiting motor units of increasing size during increasing voluntary contractions was irretrievably lost. Among patients with pressure or entrapment neuropathies, the normal orderly pattern of recruiting motor units was always retained. Similarly, in patients with motor neurone disease (amyotrophic lateral sclerosis), the orderly pattern of recruitment was not disrupted.