Electromyographic analysis of muscles across the elbow joint.

An electromyographic (EMG) technique was developed to study simultaneously the eight major elbow muscles in five normal subjects. Recordings of EMG activity in elbow muscles were obtained while the elbow joint was subjected to resisted flexion, extension, abduction, and adduction functions. The results indicate that activity in the major elbow muscles is determined by the size of the resultant flexion and extension moments created about the elbow joint, but not by varus and valgus moments. These results support the hypothesis that determination of muscle force about a joint depends on joint constraint, namely, the degree of freedom, the resultant joint forces and moments due to externally applied load, and also the function of the muscle, i.e., the line of action of the muscle that crosses the joint. The data may be used to further refine the calculation of muscle force distribution across the elbow joint.