Effects of eccentrically and concentrically induced unilateral fatigue on the involved and uninvolved limbs

This study extended findings of others related to the fatigue resistance of maximum voluntary knee extension contractions performed eccentrically on a n isokinetic dynamometer. Twelve subjects performed either 75 unilateral is okinetic concentric MVCs or 75 unilateral isokinetic eccentric MVCs at 30 d egrees s(-1). A uniquely-configured dynamometer provided the opportunity to describe the effect of the concentric or eccentric fatigue protocol on the concentric or eccentric MVC force of the contralateral limb, which was not involved in the fatigue protocol, immediately following the conclusion of the fatigue protocol. Eccentric MVC of the eccentrically fatigued group dec reased significantly (13%, p = 0.001) although the decrease was significant ly smaller than that of the concentric MVC of the concentrically fatigued g roup (39%). Concentric MVC of the contralateral limb was unaffected followi ng the concentric fatigue protocol but the eccentric MVC of the contralater al Limb increased 11% (p = 0.028) following the eccentric fatigue protocol. These results suggest that eccentric MVCs are not resistant to fatigue but do follow a different time course than fatigue induced with concentric con tractions. The extent to which eccentrically performed MVCs fatigue may ref lect the influence of protocol parameters such as the isokinetic speed, the number of repetitions, the criteria by which the protocol is terminated an d the subject selection. However, the explanations for why eccentric MVCs f atigue to such a smaller extent necessitate further systematic investigatio n including electrophysiologic methods, as do the results relative to the c ontralateral leg. Both results can be considered within the framework of cu rrent thought about the disparate nature of nervous system control of eccen tric contractions. (C) 1999 Elsevier Science Ltd. All rights reserved.