Voluntary skeletal muscles: a unifying theory on the relationship of their electrical and mechanical activities.

Experiments designed to examine the relationship between electrical and mechanical events in voluntarily contracting human muscle were performed. Experiments reported in the literature, as well as our own, were categorized according to technique into one of four types: (1) isometric-isotonic, (2) isometric-anisotonic,(3) anisometric-isotonic or (4) anisometric-anisotonic. A general relationship between the absolute value of the surface electromyogram (the absolute value of E and the force (F) generated by the contraction is proposed. This is the integral of the absolute value of E dt = k-1integralF dx i-2integralF dt, where k-1 and k-2 are constants. In the isometric-isotonic condition, this equation reduces to a linear relation between the average electromyogram and the force of contraction. A quadratic relation exists in the isometric-anisotonic, constantly increasing contraction, between the integrated electromyogram and the force of contraction. Also, this equation predicts linear relations for anisometric-isotonic contractions, and quadratic relations for an accelerated rate of contraction, between the average electromyogram and force of contraction. Both the data reported in the literature and our data provide confirmatory evidence for the unifying theory offered in this paper.