Partially Activated Human Skeletal Muscle: An Experimental Investigation of Force, Velocity, and EMG

Abstract

Experiments are described which establish quantitative relations between muscular force, contraction velocity, and the electrical activity of the muscle (as measured by the surface EMG) under conditions of steady motion. The six subjects who participated in these experiments were all athletes. Test results confirm that human skeletal muscle in vivo behaves differently when it is contracting under load than when it is extending under load. At maximum voluntary effort the force-velocity relation is similar to that found for excised, tetanized muscle (Hill’s equation). Antagonist activity was found to be low under all conditions of load and velocity. Simple equations are proposed to describe the observed force-velocity-activation relations. The parameters of these equations, which represent the apparent internal friction properties of the muscles, are evaluated and reported.