Muscle focus: a new biomechanical-based index on the selectivity of EMG activity and its application in quantifying the muscle coactivation patterns during isometric torque generation at the elbow and shoulder

Electromyographic (EMG) recordings are widely used in the study of sensorimotor and neuromuscular systems, more specifically, in the measurement of the muscle activation patterns during isometric torque generation at the elbow and shoulder. In this paper, we introduce a new biomechanics based index of muscle focus. This new index quantifies the degree of selectivity in muscle activation during a shoulder/elbow motor task with a scalar. The muscle focus takes into account both muscle co-activation and muscle cocontraction (which is a special case of co-activation caused by activation of agonist and antagonist muscles about a single joint).