ELECTRO-MYOGRAPHIC STUDY ON THE FUNCTIONAL DIFFERENTIATION OF THE HAND AND FOOT MUSCLES

Abstract

The discharges of a single NMU of a muscle under constant voluntary contraction were recorded, and the standard deviations of the discharge intervals were plotted against the mean discharge intervals. The muscles used were the M. abductor pollicis brevis, Hexor pollicis brevis, the lumbricales of the hand, and the M. abductor hallucis and flexor hallucis brevis of the foot.
(1) All the muscles showed invariably two kinds of distribution-the K-and T-curves, indicating respectively kinetic and tonic activities of NMU.
(2) In the hand muscles much of the points obtained fell around the K-curve; presumably they are composed mainly of kinetic NMU. Conversely, the foot muscles seem to contain more tonic elements, because the large portion of the points fell around T-types; moreover, they seem more tonic than the corresponding muscles of the hand. These findings may explain the functional differentiation existing in the two groups of muscles, facilitating the quick and dynamic movements of the hand, or allowing slow and static activities of the foot muscles in maintaining posture while standing or walking.
(3) All the curves start with horizontal portions of certain durations. This circumstance may be interpreted as a fair evidence of the existence of a control mechanism in maintaining voluntary contraction.