Document Detail

Muscle activation and the slow component rise in oxygen uptake during cycling.
MedLine Citation:
PMID:  11128849     Owner:  NLM     Status:  MEDLINE    
PURPOSE: During constant-rate high-intensity exercise, a steady state for oxygen uptake (VO2) is not achieved and, after the initial rapid increase, VO2 continues to increase slowly. The mechanism underlying the slow-component rise in VO2 during high-intensity exercise is unknown. It has been hypothesized that increased muscle use may be a contributing factor, but only limited electromyograph (EMG) data are available supporting this hypothesis. The purpose of this study was to determine whether there is an association between the VO2 slow component and muscle use assessed by contrast shifts in magnetic resonance images (magnetic resonance imaging (MRI)). METHODS: The VO2 slow component was measured in 16 subjects during two 15-min bouts of cycling performed at high and low intensities. EMG and MRI transverse relaxation times (T2) were obtained after 3 and 15 min to determine muscle activity at each intensity. RESULTS: Low-intensity cycling produced no VO2 slow component, and no increases in muscle activity, except for a small increase (P < 0.05) in the T2 of the vastus lateralis. During high-intensity cycling, VO2, T2 of the vastus lateralis, rectus femoris and whole leg, and EMG activity and median power frequency of the vastus lateralis rose significantly (P < 0.05) from 3 to 15 min. Percent increases in VO2 and muscle T2 were related during high-intensity cycling (r = 0.63), but not during low-intensity cycling (r = 0.00). CONCLUSION: We conclude that increased muscle use is in part responsible for the slow component rise in oxygen uptake. The results support the hypothesis that during constant-rate exercise at intensities above lactate threshold, progressively greater use of fast-twitch motor units increases energy demand and causes concomitant progressive increases in VO2 and lactate.
M J Saunders; E M Evans; S A Arngrimsson; J D Allison; G L Warren; K J Cureton
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Publication Detail:
Type:  Clinical Trial; Journal Article    
Journal Detail:
Title:  Medicine and science in sports and exercise     Volume:  32     ISSN:  0195-9131     ISO Abbreviation:  Med Sci Sports Exerc     Publication Date:  2000 Dec 
Date Detail:
Created Date:  2000-12-20     Completed Date:  2001-04-12     Revised Date:  2004-11-17    
Medline Journal Info:
Nlm Unique ID:  8005433     Medline TA:  Med Sci Sports Exerc     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2040-5     Citation Subset:  IM; S    
Department of Exercise Science, The University of Georgia, Athens, USA.
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MeSH Terms
Exercise / physiology*
Exercise Test
Lactic Acid / blood
Magnetic Resonance Imaging
Muscle Fibers, Fast-Twitch / physiology
Muscle, Skeletal / physiology*
Oxygen Consumption*
Prospective Studies
Reg. No./Substance:
50-21-5/Lactic Acid

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

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