Document Detail

Sodium-free fluid ingestion decreases plasma sodium during exercise in the heat.
MedLine Citation:
PMID:  10368348     Owner:  NLM     Status:  MEDLINE    
This study assessed whether replacing sweat losses with sodium-free fluid can lower the plasma sodium concentration and thereby precipitate the development of hyponatremia. Ten male endurance athletes participated in one 1-h exercise pretrial to estimate fluid needs and two 3-h experimental trials on a cycle ergometer at 55% of maximum O2 consumption at 34 degrees C and 65% relative humidity. In the experimental trials, fluid loss was replaced by distilled water (W) or a sodium-containing (18 mmol/l) sports drink, Gatorade (G). Six subjects did not complete 3 h in trial W, and four did not complete 3 h in trial G. The rate of change in plasma sodium concentration in all subjects, regardless of exercise time completed, was greater with W than with G (-2.48 +/- 2.25 vs. -0.86 +/- 1.61 mmol. l-1. h-1, P = 0.0198). One subject developed hyponatremia (plasma sodium 128 mmol/l) at exhaustion (2.5 h) in the W trial. A decrease in sodium concentration was correlated with decreased exercise time (R = 0.674; P = 0.022). A lower rate of urine production correlated with a greater rate of sodium decrease (R = -0. 478; P = 0.0447). Sweat production was not significantly correlated with plasma sodium reduction. The results show that decreased plasma sodium concentration can result from replacement of sweat losses with plain W, when sweat losses are large, and can precipitate the development of hyponatremia, particularly in individuals who have a decreased urine production during exercise. Exercise performance is also reduced with a decrease in plasma sodium concentration. We, therefore, recommend consumption of a sodium-containing beverage to compensate for large sweat losses incurred during exercise.
D M Vrijens; N J Rehrer
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Publication Detail:
Type:  Clinical Trial; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  86     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  1999 Jun 
Date Detail:
Created Date:  1999-08-02     Completed Date:  1999-08-02     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:  1847-51     Citation Subset:  IM    
School of Physical Education, Otago University, Dunedin, New Zealand.
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MeSH Terms
Aldosterone / blood
Blood Glucose / metabolism
Blood Volume / physiology
Body Temperature / physiology
Exercise / physiology*
Heart Rate / physiology
Hot Temperature / adverse effects*
Lactic Acid / metabolism
Oxygen Consumption / physiology
Sodium / blood,  metabolism*,  urine
Water-Electrolyte Balance / physiology
Reg. No./Substance:
0/Blood Glucose; 50-21-5/Lactic Acid; 52-39-1/Aldosterone; 7440-23-5/Sodium
Comment In:
J Appl Physiol (1985). 2006 Apr;100(4):1433; author reply 1433-4   [PMID:  16540721 ]

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