Protection of muscle membrane excitability during prolonged cycle exercise with glucose supplementation

J Appl Physiol (1985). 2007 Jul;103(1):331-9. doi: 10.1152/japplphysiol.01170.2006. Epub 2007 Apr 5.

Abstract

To determine if exercise-induced depressions in neuromuscular function are altered with oral glucose supplementation, 15 untrained participants (Vo2 peak = 45 +/- 2 ml x kg(-1) x min(-1), mean +/- SE) performed prolonged cycle exercise at approximately 60% Vo2 peak on two occasions: without glucose supplementation (NG) and with oral glucose supplementation (G). The oral G began at 30 min of exercise and was administered every 15 min (total ingested = 1.23 +/- 0.11 g carbohydrate/kg body mass). Quadriceps isometric properties and membrane excitability were assessed prior to exercise, after 90 min of exercise, and at fatigue. Cycle time to fatigue was greater (P < 0.05) in G compared with NG (137 +/- 7 vs. 115 +/- 6 min). Progressive reductions (P < 0.05) in maximal voluntary contraction (MVC, N) were observed for NG at 90 min (441 +/- 29) and at fatigue (344 +/- 33) compared with pre-exercise (666 +/- 30). At fatigue in G, the reduction in MVC was not as pronounced (P < 0.05) as in NG. Motor unit activation assessed with the interpolated twitch technique during an MVC following exercise was not different between conditions. During cycling, the G condition also resulted in a higher (P < 0.05) muscle compound potential (M-wave) amplitude (mV) at both 90 min (+50%) and at fatigue (+87%) compared with NG. Similar effects were also found M-wave area (mV/ms). These results suggest that the ergogenic effect of glucose supplementation occurs not as a result of decreased neural activation but to improved muscle function, possibly as a consequence of protection of muscle membrane excitability.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / drug effects
  • Administration, Oral
  • Beverages*
  • Blood Glucose / metabolism
  • Electromyography
  • Exercise / physiology*
  • Female
  • Glucose / administration & dosage*
  • Humans
  • Male
  • Motor Neurons / drug effects
  • Muscle Contraction / drug effects*
  • Muscle Fatigue / drug effects*
  • Muscle Strength / drug effects
  • Oxygen Consumption / drug effects
  • Quadriceps Muscle / drug effects*
  • Quadriceps Muscle / innervation
  • Quadriceps Muscle / metabolism
  • Research Design
  • Sarcolemma / drug effects*
  • Sarcolemma / metabolism
  • Time Factors

Substances

  • Blood Glucose
  • Glucose