ESTIMATING THE CONTRIBUTION OF MUSCLES TO JOINT TORQUE BASED ON MOTOR-UNIT ACTIVITY

Because most joints in the human arm are crossed by a number of muscle s which exceeds the number of degrees of Freedom for those joints, the motor system can use a variety of muscle activation patterns for the same torque in each joint. We have developed a model to estimate the c ontribution of individual muscles to the total torque in a joint based on intramuscular EMG recordings. EMG activity recorded with surface e lectrodes may be contaminated with cross-talk from other muscles. More over, it may not be representative for the activation of a muscle when there are several subpopulations of motor units in the muscle. We der ive a relation between the recruitment threshold of a motor unit in a subpopulation for force in various directions and the relative contrib ution by that subpopulation to joint torque. A set of linear equations can then be constructed which relates the contribution of each subpop ulation (and therefore of each muscle) to the total joint torque. If t he activition of individual subpopulations is modulated differently fo r forces in various directions, the relative contribution of the indiv idual subpopulations to the total joint torque dan be estimated. Copyr ight (C) 1996 Elsevier Science Ltd.