Electromyographic study of two-joint muscles.

To determine the nervous control of two-joint muscles and their coordination with other muscles in monoarticular and biarticular motions, action patterns of important two-joint muscles (rectus femoris and the medial hamstrings) and related one-joint muscles were observed. The EMG analysis of ten subjects led to the conclusion that the effect of contraction of two-joint muscles is never limited to one joint; whenever a two-joint muscle participates in a monoarticular motion its role shifts in close coordination with the other muscles. In biarticular concurrent motion the activity of the rectus femoris and the medial hamstrings is inhibited when they are antagonists, especially when motion of the knee is concerned.