Effects of Muscular Fatigue on the Performance of Handgrip Tasks During Force Generation and Relaxation

This study investigated the effects of muscular fatigue on the accuracy of force control in the respective generation and relaxation phases while performing an isometric handgrip force-tracking task. Participants were instructed to track a target line moving upward and downward, corresponding to 0 to 30% of maximum voluntary contraction (MVC) at a constant for 7 s. Eight sets of 25 continuous trials each were conducted. The force-tracking accuracy and electromyography (EMG) of extensor carpi radialis (ECR) and flexor carpi ulnaris (FCU) were evaluated. The force-tracking accuracy was compared between the phase (upward: generation and downward: relaxation), set (first and eighth), and within-set periods (early: 1-5, middle: 10-15, and late: 20-25 trials). The force-tracking accuracy at the middle and late periods significantly declined compared to the early period in the relaxation phase. Integrated EMG of ECR and FCU was significantly larger in the generation than in the relaxation phase. The integrated EMG of FCU in the generation phase was significantly different between the periods. Furthermore, the median frequency of FCU was significantly different between the phases and periods. These findings suggest that the effects of muscular fatigue on force control varied between generation and relaxation due to the amount and frequency band of muscle activity.