The relationship of Motor-unit activation to isokinetic muscular contraction at different contractile velocities.

This investigation was designed to examine 1) the relationship between motor-unit activation (as recorded by integrated EMG) and speed of contraction and 2) the relationship between mechanical work, power output, peak torque, average torque, and both velocity of movement and integrated electromyographic recordings in the elbow flexor muscles. A series of isokinetic contractions of the elbow flexor muscles was performed by six normal subjects over a range of contractile velocities. Integrated electromyographic discharge and mechanical torque were recorded simultaneously. The results of an analysis of variance, corrected for repeated measures, indicated that both torque and motor-unit electrical activity decreased as contractile velocity increased. The relationship between torque and integrated electromyographic activity was linear and highly significant (r = .95 and r = .93). Implications of a neural interpretation of the in vivo torqu-velocity relationship in muscle are discussed.