Document Detail

Glycogen availability does not affect the TCA cycle or TAN pools during prolonged, fatiguing exercise.
MedLine Citation:
PMID:  12736189     Owner:  NLM     Status:  MEDLINE    
The hypothesis that fatigue during prolonged exercise arises from insufficient intramuscular glycogen, which limits tricarboxylic acid cycle (TCA) activity due to reduced TCA cycle intermediates (TCAI), was tested in this experiment. Seven endurance-trained men cycled at approximately 70% of peak O(2) uptake (Vo(2 peak)) until exhaustion with low (LG) or high (HG) preexercise intramuscular glycogen content. Muscle glycogen content was lower (P < 0.05) at fatigue than at rest in both trials. However, the increase in the sum of four measured TCAI (>70% of the total TCAI pool) from rest to 15 min of exercise was not different between trials, and TCAI content was similar after 103 +/- 15 min of exercise (2.62 +/- 0.31 and 2.59 +/- 0.28 mmol/kg dry wt for LG and HG, respectively), which was the point of volitional fatigue during LG. Subjects cycled for an additional 52 +/- 9 min during HG, and although glycogen was markedly reduced (P < 0.05) during this period, no further change in the TCAI pool was observed, thus demonstrating a clear dissociation between exercise duration and the size of the TCAI pool. Neither the total adenine nucleotide pool (TAN = ATP + ADP + AMP) nor IMP was altered compared with rest in either trial, whereas creatine phosphate levels were not different when values measured at fatigue were compared with those measured after 15 min of exercise. These data demonstrate that altered glycogen availability neither compromises TCAI pool expansion nor affects the TAN pool or creatine phosphate or IMP content during prolonged exercise to fatigue. Therefore, our data do not support the concept that a decrease in muscle TCAI during prolonged exercise in humans compromises aerobic energy provision or is the cause of fatigue.
Jacinta Baldwin; Rodney J Snow; Martin J Gibala; Andrew Garnham; Krista Howarth; Mark A Febbraio
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Publication Detail:
Type:  Journal Article     Date:  2002-11-27
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  94     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2003 Jun 
Date Detail:
Created Date:  2003-05-08     Completed Date:  2003-07-23     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2181-7     Citation Subset:  IM    
Department of Physiology, University of Melbourne, Parkville 3010, Victoria, Australia.
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MeSH Terms
Adenine Nucleotides / metabolism*
Amino Acids / metabolism
Blood Glucose / analysis
Citric Acid Cycle / physiology*
Exercise / physiology*
Fatigue / etiology*
Glycogen / metabolism*
Heart Rate
Hypoxanthine / blood,  metabolism
Inosine Monophosphate / metabolism
Lactic Acid / blood,  metabolism
Muscle, Skeletal / metabolism
Oxygen Consumption
Pyruvates / metabolism
Time Factors
Reg. No./Substance:
0/Adenine Nucleotides; 0/Amino Acids; 0/Blood Glucose; 0/Pyruvates; 131-99-7/Inosine Monophosphate; 50-21-5/Lactic Acid; 68-94-0/Hypoxanthine; 9005-79-2/Glycogen
Comment In:
J Appl Physiol (1985). 2004 Apr;96(4):1571-2; author reply 1572-3   [PMID:  15016797 ]

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

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