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Specificity of muscular fatigue and force-enhancing mechanisms in power and endurance athletes
Abstract
The purpose was to assess the specificity of muscular fatigue and changes in the stretch-evoked forces and integrated surface electromyographic (EMG) activity of the vastus lateralis and biceps femoris muscles in 12 endurance and 12 power athletes. On each of four separate days, fatigue was induced with 49 repetitions of isometric, shortening, and lengthening knee extension and with 1-min continuous vertical jumping. Before and after fatigue, testing included 5-s isometric knee extension with a superimposed stretch, shortening, and lengthening knee extension. Endurance and power athletes produced significantly greater lengthening and stretch forces compared to isometric and shortening forces. Within each group, lengthening and stretch forces were not different. Isometric force was significantly greater than shortening force in power but not in endurance athletes. Power athletes averaged 57.4% stronger than endurance athletes for the three measures of knee extension strength. Power athletes produced significantly more integrated EMG during isometric, shortening, and lengthening knee extension than endurance athletes, but there were no between-group differences in the integrated EMG of the biceps femoris. Endurance athletes showed significantly less stretch-evoked force potentiation (10.4 N x 10) than power athletes (14.4 N x 10). Expressed as a percentage of isometric force, the superimposed stretch increased force production by 20% in endurance and 15% in power athletes. The integrated EMG due to the stretch increased by 37.6 and 21.7 $\mu$V$\cdot$s or 23% and 15% in power and in endurance athletes. Based on the stretch-evoked force-to-EMG ratios, endurance athletes used approximately twice as much neural drive to potentiate the same amount of force as power athletes. Endurance athletes showed significantly less force fatigue ($\sim$7%) than power athletes (26%) for isometric, shortening, and lengthening knee extension exercise. Muscular fatigue was the greatest with lengthening exercise in power but not in endurance athletes, 5 of whom increased lengthening force by the 49th repetition. Fatigue in the endurance athletes was the greatest after the 1-min vertical jumping protocol (-6.4%). The average decline in the integrated EMG of the vastus lateralis was 17% and 22% in endurance and power athletes. Stretch-evoked force did not change with fatigue, while EMG potentiation significantly declined after the four fatigue protocols in both groups. For the endurance and power athletes, there was no indication for specificity of force or EMG fatigue. Thus, the current data suggest that in two groups of athletes, muscular fatigue was general in terms of force loss and EMG activity assessed by three test modes and four fatigue protocols.
Subject Area
Neurosciences|Physical education|Physiology
Recommended Citation
Hortobagyi, Tibor, "Specificity of muscular fatigue and force-enhancing mechanisms in power and endurance athletes" (1990). Doctoral Dissertations Available from Proquest. AAI9035392.
https://scholarworks.umass.edu/dissertations/AAI9035392