Document Detail

Water and electrolyte shifts with partial fluid replacement during exercise.
MedLine Citation:
PMID:  10483801     Owner:  NLM     Status:  MEDLINE    
In this study, we examined whether athletes, who typically replace only approximately 50% of their fluid losses during moderate-duration endurance exercise, should attempt to replace their Na+ losses to maintain extracellular fluid volume. Six male cyclists performed three 90-min rides at 65% of peak O2 uptake in a 32 degrees C environment and ingested either no fluid (NF), 1.21 of water (W), or saline (S) containing 100 mmol of NaCl x l(-1) to replace their electrolyte losses. Both W and S conditions decreased final heart rates by approximately 10 betas min(-1) (P<0.005) and reduced falls in plasma volume (PV) by approximately 4% (P<0.05). Maintenance of PV after 10 min in the W trial prevented further rises in plasma concentrations of Na+ [Na+], Cl- and protein but in the S and NF trials, plasma [Na+] continued to increase by approximately 4 mEq x l(-1). Differences in plasma [Na+] had little effect on the approximately 2.4 l fluid, approximately 120 mEq Na+ and approximately 50 mEq K+ losses in sweat and urine in the three trials. The main effects of W and S were on body fluid shifts. During the NF trial, PV and interstitial fluid (ISF) and intracellular fluid (ICF) volumes decreased by approximately 0.1, 1.2 and 1.0 l, respectively. In the W trial, the approximately 1.2 l fluid and approximately 120 mEq Na+ losses contracted the ISF volume, and in the S trial, ISF volume was maintained by the movement of water from the ICF. Since the W and S trials were equally effective in maintaining PV, Na+ ingestion may not be of much advantage to athletes who typically replace only approximately 50% of their fluid losses during competitive endurance exercise.
B Sanders; T D Noakes; S C Dennis
Publication Detail:
Type:  Clinical Trial; Journal Article; Randomized Controlled Trial; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  European journal of applied physiology and occupational physiology     Volume:  80     ISSN:  0301-5548     ISO Abbreviation:  Eur J Appl Physiol Occup Physiol     Publication Date:  1999 Sep 
Date Detail:
Created Date:  1999-10-19     Completed Date:  1999-10-19     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0410266     Medline TA:  Eur J Appl Physiol Occup Physiol     Country:  GERMANY    
Other Details:
Languages:  eng     Pagination:  318-23     Citation Subset:  IM; S    
Medical Research Council and University of Cape Town Bioenergetics of Exercise Research Unit, Sports Science Institute of South Africa, Newlands.
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MeSH Terms
Bicycling / physiology
Electrolytes / blood,  urine
Exercise / physiology*
Exercise Test
Fluid Shifts / physiology*
Fluid Therapy*
Oxygen Consumption / physiology
Sodium / physiology
Sweat / chemistry,  metabolism
Water-Electrolyte Balance / physiology*
Reg. No./Substance:
0/Electrolytes; 7440-23-5/Sodium

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

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