Contractile and electrical properties of human motor units in neuropathies and motor neurone disease

The contractile and electrical properties of motor units in the first dorsal interosseous muscle of the hand have been studied in 26 patients with ulnar neuropathies and motor neurone disease (amyotrophic lateral sclerosis). Among patients with unilateral pressure or entrapment ulnar neuropathies, there was a tendency for the twitch tensions for single motor units to be smaller, while the surface EMG amplitudes were generally larger in the affected hands. Very large EMG amplitudes but normal size twitch tensions were observed among the motor neurone disease patients, indicating that, in general, motor units enlarged by sprouting are less efficient contractile units than units of normal physiological size.