The relative activation of elbow-flexor muscles in isometric flexion and in flexion/extension movements

Coordination studies of multi-joint movements suggest that the central nervous system uses some constraints to reduce the large number of degrees of freedom of the arm. To gain insight into how the net joint torque is distributed among the muscles, intramuscular EMG recordings were made to determine the relative activation of five major elbow-flexor muscles during isometric, shortening, and lengthening contractions at three elbow joint angles. A regularization procedure was used to evaluate the effect of two different approaches used to calculate the relative contribution of elbow-flexor muscles to joint torque from intramuscular EMG recordings. The results demonstrate a significant increase of the relative contribution of the biarticular muscles for more extended elbow joint angles and for isotonic tasks relative to isometric tasks.