Document Detail

Substrate utilization during exercise in active people.
MedLine Citation:
PMID:  7900696     Owner:  NLM     Status:  MEDLINE    
When people walk at low intensity after fasting, the energy needed is provided mostly by oxidation of plasma fatty acids. As exercise intensity increases (eg, to moderate running), plasma fatty acid turnover does not increase and the additional energy is obtained by utilization of muscle glycogen, blood glucose, and intramuscular triglyceride. Further increases in exercise intensity are fueled mostly by increases in muscle glycogen utilization with some additional increase in blood glucose oxidation. Muscle glycogen and blood glucose contribute equally to carbohydrate energy production over 2-3 h of moderate-intensity exercise; fatigue develops when these substrates are depleted. Active people can deplete muscle glycogen with 30-60 min of high intensity, intermittent exercise. When the ingestion of dietary carbohydrate is optimal, it is possible to resynthesize muscle glycogen to high concentrations in approximately 24 h, which is the major factor in recovery of exercise tolerance. However, this requires that a 70-kg person eat at least 50 g carbohydrate per every 2 h, beginning soon after exercise, and ingest 500-600 g in 24 h (ie; approximately 7-9 g/kg body wt). Carbohydrate foods eliciting high glycemic and insulinemic responses promote more rapid glycogen resynthesis than do foods eliciting lower glycemic responses. Therefore, foods ingested for energy before, during, or after exercise should be classified according to their glycemic index. Although carbohydrate ingestion before and during exercise adds exogenous substrate to the body, it usually attenuates plasma fatty acid mobilization and oxidation.
E F Coyle
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Publication Detail:
Type:  Journal Article; Review    
Journal Detail:
Title:  The American journal of clinical nutrition     Volume:  61     ISSN:  0002-9165     ISO Abbreviation:  Am. J. Clin. Nutr.     Publication Date:  1995 Apr 
Date Detail:
Created Date:  1995-04-27     Completed Date:  1995-04-27     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0376027     Medline TA:  Am J Clin Nutr     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  968S-979S     Citation Subset:  AIM; IM; S    
Department of Kinesiology and Health Education, University of Texas at Austin 78712.
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MeSH Terms
Dietary Carbohydrates / administration & dosage
Energy Metabolism*
Exercise / physiology*
Fatty Acids / blood
Glycogen / biosynthesis,  metabolism
Muscles / metabolism
Nutritional Physiological Phenomena
Reg. No./Substance:
0/Dietary Carbohydrates; 0/Fatty Acids; 9005-79-2/Glycogen

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