THE ROLE OF THE BIARTICULAR AGONIST AND COCONTRACTING ANTAGONIST PAIRIN ISOMETRIC MUSCLE FATIGUE

Isometric knee extensions until exhaustion at 30%, 50%, and 70% of max imum voluntary contraction were performed by 18 healthy subjects, Duri ng muscle fatigue, surface electromyographic activity was recorded fro m the knee-extensors vastus lateralis, vastus medialis, and rectus fem oris, and the coactive antagonistic biceps femoris. The electromyograp hic parameter median frequency (MF) served as a measure of fatigue. Co efficients of regression of the MF fatigue changes were analyzed stati stically. MF fatigue occurred within the coactive biceps femoris and w as significantly more pronounced than in the quadriceps. When the MF f atigue shifts of the coactive biceps femoris were compared with each o f the three investigated parts of the quadriceps separately, MF fatigu e shifts were similar in shape for the biarticular coactive biceps fem oris and the biarticular rectus femoris, but differed significantly be tween the biceps femoris and the two monoarticular muscles, vastus med ialis and vastus lateralis. As both the biarticular agonist and coacti ve antagonist muscles fatigued at a higher rate than the two monoartic ular muscles, it seems likely that this biarticular agonist/antagonist pair determines the time to the limit of endurance. (C) 1998 John Wil ey & Sons, Inc.