THE MEASUREMENT OF THE ELASTICITY AND VISCOSITY OF SKELETAL MUSCLE IN NORMAL AND PATHOLOGICAL CASES; A STUDY OF SOCALLED “MUSCLE TONUS”

Abstract

An apparatus is described which alternately flexes and extends the leg at the knee at regulated angular velocities and records simultaneously the necessary torque which is applied to the leg for this purpose. The force so recorded is not zero at zero velocity and this residuum is a static measure of muscle "tonus" and is found to be large in clinically spastic subjects. It is equivalent to a measure of the elasticity of the muscles. The force (F) increases more or less linearly with increase in velocity of movement (V) and this rate of increase of F (dF/dV) is a kinetic measure of the muscle "tonus" and serves for a calculation of the coefficient of viscosity of the leg. The average value for normal legs is 28 gm. per cm.2 of muscle cross section for a velocity of stretch of 1 cm. per cm. muscle length per sec. Some legs classified clinically as spastic give normal values when tested by this apparatus. It appears to be due to the slow speeds of movement which are attained by the apparatus which are not adequate to reach the threshold for the stretch reflexes responsible for the spasticity observed clinically.