Motor unit potentials at high muscle activity recorded by selective electrodes.

The selectivity of different kinds of electrodes for recording of single motor unit potentials was theoretically evaluated. A new type of selective "branched", superficial and subcutaneous wire electrodes was described. The discharge of single alpha motoneurons during movements against elastic resistance was investigated studying motor unit potentials in m. biceps brachii and m.interosseus dorsalis l. Depending on the velocity of the movement, the following pattern of discharge was found: 1) At slow velocity the frequency of discharge increased and new motor units were recruited. 2) At higher velocity the frequency of discharge was constant. The muscle force increased only when new motor units were recruited. 3) At very quick ballistic movements the frequency of discharge decreased during the movement.