Document Detail

Muscle Na-K-pump and fatigue responses to progressive exercise in normoxia and hypoxia.
MedLine Citation:
PMID:  15860645     Owner:  NLM     Status:  MEDLINE    
To investigate the effects of hypoxia and incremental exercise on muscle contractility, membrane excitability, and maximal Na(+)-K(+)-ATPase activity, 10 untrained volunteers (age = 20 +/- 0.37 yr and weight = 80.0 +/- 3.54 kg; +/- SE) performed progressive cycle exercise to fatigue on two occasions: while breathing normal room air (Norm; Fi(O(2)) = 0.21) and while breathing a normobaric hypoxic gas mixture (Hypox; Fi(O(2)) = 0.14). Muscle samples extracted from the vastus lateralis before exercise and at fatigue were analyzed for maximal Na(+)-K(+)-ATPase (K(+)-stimulated 3-O-methylfluorescein phosphatase) activity in homogenates. A 32% reduction (P < 0.05) in Na(+)-K(+)-ATPase activity was observed (90.9 +/- 7.6 vs. 62.1 +/- 6.4 protein(-1).h(-1)) in Norm. At fatigue, the reductions in Hypox were not different (81 +/- 5.6 vs. 57.2 +/- 7.5 protein(-1).h(-1)) from Norm. Measurement of quadriceps neuromuscular function, assessed before and after exercise, indicated a generalized reduction (P < 0.05) in maximal voluntary contractile force (MVC) and in force elicited at all frequencies of stimulation (10, 20, 30, 50, and 100 Hz). In general, no differences were observed between Norm and Hypox. The properties of the compound action potential, amplitude, duration, and area, which represent the electromyographic response to a single, supramaximal stimulus, were not altered by exercise or oxygen condition when assessed both during and after the progressive cycle task. Progressive exercise, conducted in Hypox, results in an inhibition of Na(+)-K(+)-ATPase activity and reductions in MVC and force at different frequencies of stimulation; these results are not different from those observed with Norm. These changes occur in the absence of reductions in neuromuscular excitability.
S D Sandiford; H J Green; T A Duhamel; J D Schertzer; J D Perco; J Ouyang
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Publication Detail:
Type:  Clinical Trial; Journal Article; Randomized Controlled Trial; Research Support, Non-U.S. Gov't     Date:  2005-04-28
Journal Detail:
Title:  American journal of physiology. Regulatory, integrative and comparative physiology     Volume:  289     ISSN:  0363-6119     ISO Abbreviation:  Am. J. Physiol. Regul. Integr. Comp. Physiol.     Publication Date:  2005 Aug 
Date Detail:
Created Date:  2005-07-14     Completed Date:  2005-09-01     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  100901230     Medline TA:  Am J Physiol Regul Integr Comp Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  R441-R449     Citation Subset:  IM    
Dept. of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
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MeSH Terms
Anoxia / enzymology,  physiopathology*
Muscle Fatigue*
Muscle, Skeletal / enzymology,  physiopathology*
Oxygen / blood
Oxygen Consumption
Sodium-Potassium-Exchanging ATPase / metabolism*
Reg. No./Substance:
7782-44-7/Oxygen; EC ATPase

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

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