Motor output is more variable during eccentric compared with concentric contractions

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Abstract
This study examined the ability of 10 young (25.3 +/- 2.8 yr) healthy individuals to control knee-extension force during several discrete concentric and eccentric contractions. Subjects performed maximal and submaximal tasks on a KIN-COM isokinetic dynamometer. The submaximal tasks were to match a force-time parabola with a time to peak force of 200 ms at five target-forces (50, 100, 150, 200, and 250 N). Mean peak force produced by the subjects at each target-force during concentric and eccentric contractions was similar. Mean time to peak force, however, was much shorter for eccentric contractions and was not influenced by increases in the level of force. The standard deviation (SD) and coefficient of variation (CV) of peak force was greater during eccentric compared with concentric contractions. The SD of time to peak force was greater for concentric contractions; however, when normalized to the mean time to peak force produced (CV), eccentric contractions were more variable. Results provide evidence that even in young adults the control of motor output is different for eccentric compared with concentric contractions.