Document Detail

Effects of 3 days of carbohydrate supplementation on muscle glycogen content and utilisation during a 1-h cycling performance.
MedLine Citation:
PMID:  9189727     Owner:  NLM     Status:  MEDLINE    
This study compared the effects of supplementing the normal diets of six trained cyclists [maximal oxygen uptake (VO2max) 4.5 (0.36) l.min-1; values are mean (SD)] with additional carbohydrate (CHO) on muscle glycogen utilisation during a 1-h cycle time-trial (TT). Using a randomised crossover design, subjects consumed either their normal diet (NORM) for 3 days, which consisted of 426 (137) CHO [5.9 (1.4) g. kg-1 body mass (BM)], or additional CHO (SUPP) to increase their intake to 661 (76) [9.3 (0.7) g. kg-1 BM]. The SUPP diet elevated muscle glycogen content from 459 (83) to 565 (62) dry weight (d.w.) (P < 0.05). However, despite the increased pre-exercise muscle glycogen stores, there was no difference in the distance cycled during the TT [40.41 (1.44) vs 40.18 (1.76) km for NORM and SUPP, respectively]. With NORM, muscle glycogen declined from 459 (83) to 175 (64) d.w., whereas with SUPP the corresponding values were 565 (62) and 292 (113) d.w. Accordingly, both muscle glycogen utilisation [277 (64) vs 273 (114) d.w.] and total CHO oxidation [169 (20) vs 165 (30) g.h-1 for NORM and SUPP, respectively] were similar. Neither were there any differences in plasma glucose or lactate concentrations during the two experimental trials. Plasma glucose concentration averaged 5.5 (0.5) and 5.6 (0.6) mmol.l-1, while plasma lactate concentration averaged 4.4 (1.9) and 4.4 (2.3) mmol.l-1 for NORM and SUPP, respectively. The results of this study show that when well-trained subjects increase the CHO content of their diet for 3 days from 6 to 9 BM there is only a modest increase in muscle glycogen content. Since supplementary CHO did not improve TT performance, we conclude that additional CHO provides no benefit to performance for athletes who compete in intense, continuous events lasting 1 h. Furthermore, the substantial muscle CHO reserves observed at the termination of exercise indicate that whole-muscle glycogen depletion does not determine fatigue at this exercise intensity and duration.
J A Hawley; G S Palmer; T D Noakes
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Publication Detail:
Type:  Clinical Trial; Journal Article; Randomized Controlled Trial; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  European journal of applied physiology and occupational physiology     Volume:  75     ISSN:  0301-5548     ISO Abbreviation:  Eur J Appl Physiol Occup Physiol     Publication Date:  1997  
Date Detail:
Created Date:  1997-08-01     Completed Date:  1997-08-01     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0410266     Medline TA:  Eur J Appl Physiol Occup Physiol     Country:  GERMANY    
Other Details:
Languages:  eng     Pagination:  407-12     Citation Subset:  IM; S    
Department of Physiology, University of Cape Town Medical School, South Africa.
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MeSH Terms
Bicycling / physiology*
Blood Glucose / metabolism
Cross-Over Studies
Dietary Carbohydrates / administration & dosage*
Exercise / physiology*
Food, Fortified
Glycogen / biosynthesis*
Lactic Acid / blood,  metabolism
Muscle, Skeletal / physiology*
Reg. No./Substance:
0/Blood Glucose; 0/Dietary Carbohydrates; 50-21-5/Lactic Acid; 9005-79-2/Glycogen

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