Reduced neuromuscular activity and force generation during prolonged cycling.
We examined neuromuscular activity during stochastic (variable intensity) 100-km cycling time trials (TT) and the effect of dietary carbohydrate manipulation. Seven endurance-trained cyclists performed two 100-km TT that included five 1-km and four 4-km high-intensity epochs (HIE) during which power output, electromyogram (EMG), and muscle glycogen data were analyzed. The mean power output of the 4-km HIE decreased significantly throughout the trial from 319 +/- 48 W for the first 4-km HIE to 278 +/- 39 W for the last 4-km HIE (P < 0.01). The mean integrated EMG (IEMG) activity during the first 4-km HIE was 16.4 +/- 9.8% of the value attained during the pretrial maximal voluntary contraction (MVC). IEMG decreased significantly throughout the trial, reaching 11.1 +/- 5.6% during the last 4-km HIE (P < 0.01). The study establishes that neuromuscular activity in peripheral skeletal muscle falls parallel with reduction in power output during bouts of high-intensity exercise. These changes occurred when <20% of available muscle was recruited and suggest the presence of a central neural governor that reduces the active muscle recruited during prolonged exercise.
St Clair Gibson
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MRC/UCT Research Unit of Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town Medical School, Cape Town, 7725 South Africa. agibson@sports.uct.ac.za
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Noakes
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D000328:Adult; D001642:Bicycling / Q000502:physiology; D004040:Dietary Carbohydrates / Q000493:pharmacokinetics; D004576:Electromyography; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*
D004040:Dietary Carbohydrates; D006003:Glycogen