Motor control during a precision grasp lift while fatigued: What are the consequences

This series of studies aimed to assess the effects of fatigue on the ability to generate motor commands appropriate for lifting objects of various weights. As well, the issue of whether fatigue is used as a parameter to update previously constructed internal models was addressed.; Participants used a precision grasp to lift objects that varied in weight under consistent (objects were visually identical on all trials) or congruent (the larger the object the heavier the object) visual conditions before and after completing a fatiguing protocol designed to induce peripheral fatigue. The consistent condition required an on-line control strategy in which haptic feedback is necessary to perform the task. With the congruent condition visual cues can be used to anticipate object mass prior to actual contact with the object. Force and movement characteristics of each lift along with perceptual judgments of object weight were measured.; Results showed that grip force scaling was present in both the consistent and congruent visual conditions as the forces elicited increased with the increasing weights of the objects. Participants in the consistent visual condition produced the same grip forces before and after completing the fatiguing protocol. However, participants in the congruent visual condition produced lower forces in the post-fatigue test than those forces produced in the pre-fatigue test. As well as showing no differences in motor outputs, participants in the consistent visual condition showed no differences in their ability to perceive the weight of the lifted objects following the fatiguing protocol. However, participants in the congruent visual condition were less accurate and perceived the weights to be heavier following fatiguing exercise.; Based on these results it is suggested that the internal representations that are a part of anticipatory control strategies are not modified to take into account peripheral fatigue. This was shown by the inability of participants in the congruent visual condition to match pre-test movement characteristics during the trials following fatiguing exercise. In addition, it was shown that when utilizing on-line motor control strategies, adaptations in motor output are made to compensate for the effects of fatiguing exercise. This was evidenced by participants in the constant visual condition as they showed no effects of fatigue motorically or perceptually.