Transient Electromyographic Responses by Isokinetic Torque Release during Mechanically Assisted Elbow Flexion

Power assistance on joint torque may not be beneficial to all the related muscles. We investigated the effects of power assistance on torque release during isokinetic elbow flexion. An isokinetic dynamometer system was used to simulate dynamic elbow flexion with power assistance, which altered the exercise conditions of baseline isometric torque (greater and lower) and rotation speed (faster and slower) of the lever arm. Ten male right-handed participants performed exercise tasks using the system. We measured (1) the electromyogram (EMG) amplitudes of the biceps brachii (BB), brachioradialis (BR), and triceps brachii (TB) muscles, (2) torque output and its variability, and (3) the perceived assistance level. Transient responses of the objective measurements were analyzed by observing three time epochs before and after power assistance. Greater variability and lower perceived assistance levels were observed when greater torque was released at a faster rotation speed. The torque output and EMG amplitudes of BB and BR muscles decreased over time. However, EMG amplitudes in the TB muscle were relatively constant until 200 ms after power assistance resulting in greater muscle co-contraction. This could be attributed to the increased postural stability of the human musculature system when the external perturbation on joint movement occurred by power assistance, independent of exercise conditions.