Dual degree of freedom tasks: Flexion effect on supination/pronation response

This study investigated the influence of an elbow flexion task, graded from 0-100% maximum voluntary contraction (MVC), on torque production and muscle activity in isometric supination and pronation MVC tasks. Torque in both degrees-of-freedom (df) and surface electromyographic (EMG) records from several sites on muscles crossing the elbow were collected as subjects performed isometric elbow supination or pronation MVCs while ostensibly maintaining a flexion torque target. Task effects were statistically tested using analysis of covariance (ANCOVA) and modelled with polynomial regression techniques. Muscular synergism was examined using a multivariate analysis of covariance (MANCOVA) model to test interactions between EMG site responses and flexion torque changes. The results demonstrate that the flexion torque level modulates the supination MVC torque level and the EMG amplitude of all monitored muscles. Further, the synergistic pattern of muscle activity was significantly influenced by the flexion df task. These results suggest that both uni- and multifunctional muscles may be influenced by dual df tasks. Comparison of these results with the dual df task literature suggests that investigating these behaviours across a full range of torque levels is critical because the present findings lead to conclusions that differ somewhat from studies investigating tasks performed only at low or high torque levels.