Issn Print: 0195-9131
Publication Date: 1996/05/01
RELATIONSHIP BETWEEN PERIPHERAL FATIGUE AND THE INHIBITION OF NEURAL ACTIVATION 838
M. R. Simpson; J. R. Burke; J. M. Davis; D. A. Jackson
Excerpt
The purpose of this study was to detect changes in neural activation of the alpha motoneuron pool due to peripheral fatigue. The interpolated twitch (IT) response at maximal and submaximal voluntary contractions were measured in 6 college-aged students before and after fatiguing isometric exercise of the soleus muscle. The fatiguing isometric exercise consisted of 5 bouts of 20 maximal voluntary contractions (MVC). One repitition required the subject to hold his MVC for 10 s and then to relax for 5 s. Throughout the pre- and post-fatigue IT trials, maximum twitches were evoked in the soleus muscle(control twitches-CT). In addition, IT at 100% MVC, MVC,and CT were recorded between the exercise bouts. MVC force and CT force decreased after the fatiguing exercise bouts by 18% and 22% respectively (p<.05). The IT force at 100% MVC increased by 128% (p<.05). Neural activation ((CT- IT/CT)*100) at 100% MVC progressively decreased from 88% to 67% after the fatiguing exercise bouts (p<.05). However, at submaximal voluntary contractions, the IT force and neural activation were similar pre- and post-fatigue (p>.05). The concomitant decrease of CT force and MVC force suggests that the predominant mechanism underlying fatigue involved peripheral factors. Consequently, the decrease in neural activation at 100% MVC with fatigue most likely reflects either an inhibition of peripheral feedback onto the alpha motoneuron pool, or a compensatory twitch potentiation effect. Neural activation may have also decreased due to a reduction in motivation(central factor) after the fatiguing exercise bouts.
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