Protection of muscle membrane excitability during prolonged cycle exercise with glucose supplementation.
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.
Stewart
R D
RD
Department of Kinesiology, University of Waterloo, Waterloo, ON Canada N2L 3G1.
Duhamel
T A
TA
Foley
K P
KP
Ouyang
J
J
Smith
I C
IC
Green
H J
HJ
D000200:Action Potentials / Q000187:drug effects; D000284:Administration, Oral; D001628:Beverages; D001786:Blood Glucose / Q000378:metabolism; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000008:administration & dosage*; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D018763:Muscle Fatigue / Q000187:drug effects*; D053580:Muscle Strength / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D052097:Quadriceps Muscle / Q000187:drug effects* / Q000294:innervation / Q000378:metabolism; D012107:Research Design; D012508:Sarcolemma / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
D001786:Blood Glucose; D005947:Glucose