THE EFFECT OF FATIGUE AND VISUAL FEEDBACK ON SUBMAXIMAL ISOMETRIC MUSCLE CONTRACTIONS

The force production and the ability to control it is necessary to the best performance in sports. The aim of this paper is to study the effect of visual feedback and fatigue on torque accuracy. The subjects were 5 healthy young adults, who performed maximal and submaximal isometric voluntary contractions for knee extension in an isokinetics machine. The task was to maintain the isometric torque in specific values. It was measured the myoelectric activity of selected knee muscles. We found that visual feedback affected the variability and the mean activity of all muscles. Their variability and means values were higher without feedback information. We also found that fatigue affected the variability of five muscles (BF, RF, ST, VL, and VMO). Their variability was higher before fatigue. Fatigue affected the mean activity of four muscles (BF, ST, RF, and VL), and their mean activities were higher before fatigue. And finally, we found that fatigue also affected the median frequency of five muscles (BF, GL, ST, VL, and VMO). Their median frequencies were higher after fatigue exercise. We discuss those results as a consequence of joint stiffness and motor unit discharge