Document Detail

Current issues in exercise metabolism: the crossover concept.
MedLine Citation:
PMID:  9363376     Owner:  NLM     Status:  MEDLINE    
1. Since ancient times, athletes have consumed proteins because of the belief they were the necessary substrate for optimal performance. Even though this concept was proven to be incorrect before the beginning of the 19th century, the practice continued until several decades ago. 2. By 1939, careful metabolic investigations on the changes in the respiratory exchange ratio had demonstrated that the metabolic transformations of lipids and carbohydrates were the primary sources of energy for muscular exercise. 3. Metabolic investigations on the profile of energy transformations during exercise have indicated that aspects related to exercise intensity, state of training, the availability of circulating free fatty acids, the activity of the sympathetic nervous system, resting levels of muscle and liver glycogen and muscle triglyceride concentrations have to be considered to explain a specific response. 4. In 1994, Brooks and Mercier introduced the concept of 'crossover' in their review manuscript to explain the shift in substrate utilization from lipids to carbohydrates by trained subjects when the power output was increased. In addition, the concept was advanced to reconcile divergent results by different investigators. 5. In 1995, Coggan and associates investigated the glucose kinetics of non-trained and trained subjects performing power outputs equal to 80% VO2max and concluded that the crossover concept was unable to explain their metabolic results from trained subjects. 6. Because of the importance of the topic to exercise physiologists and the uncertainties the controversy has created for teachers and researchers, the American Physiological Society Section on Environmental and Exercise Physiology scheduled a Point-Counterpoint forum at the 1997 Experimental Biology Meeting. The subsequent manuscripts of Brooks and Coggan are a result of that forum.
C M Tipton
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Clinical and experimental pharmacology & physiology     Volume:  24     ISSN:  0305-1870     ISO Abbreviation:  Clin. Exp. Pharmacol. Physiol.     Publication Date:  1997 Nov 
Date Detail:
Created Date:  1997-12-18     Completed Date:  1997-12-18     Revised Date:  2005-11-17    
Medline Journal Info:
Nlm Unique ID:  0425076     Medline TA:  Clin Exp Pharmacol Physiol     Country:  AUSTRALIA    
Other Details:
Languages:  eng     Pagination:  887-8     Citation Subset:  IM; S    
Department of Physiology, University of Arizona, Tucson 85721, USA.
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MeSH Terms
Carbohydrate Metabolism
Energy Metabolism
Lipid Metabolism

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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