Axonal velocities of motor units in the hand and foot muscles of the baboon.

The axonal velocities of single motor units in the small hand and foot muscles of the baboon were studied by means of a collision technique which produced selective blocking of most of the fast-conducting fibres. In the abductor pollicis brevis muscle velocities ranged from 43 to 82 m/sec, and in the abductor digiti minimi muscle from 40 to 78 m/sec. In the extensor digitorum brevis muscle the range was 40-70 m/sec. When velocities were plotted as percentages of the maximal obtained in the same experiment, the range was similar in the 3 muscles studied. Most motor units had velocities greater than 65% of maximal but, in a few, velocities were between 55% and 65% of maximal. The possible relevance of these findings to human motor nerves is discussed.