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Protection of total body water content and absence of hyperthermia despite 2% body mass loss ('voluntary dehydration') in soldiers drinking ad libitum during prolonged exercise in cool environmental conditions.
MedLine Citation:
PMID:  21047838     Owner:  NLM     Status:  In-Data-Review    
Abstract/OtherAbstract:
The extent to which humans need to replace fluid losses during exercise remains contentious despite years of focused research. The primary objective was to evaluate ad libitum drinking on hydration status to determine whether body mass loss can be used as an accurate surrogate for changes in total body water (TBW) during exercise. Data were collected during a 14.6-km route march (wet bulb globe temperature of 14.1°C ). 18 subjects with an average age of 26±2.5 (SD) years participated. Their mean ad libitum total fluid intake was 2.1±1.4 litres during the exercise. Predicted sweat rate was 1.289±0.530 l/h. There were no significant changes (p>0.05) in TBW, urine specific gravity or urine osmolality despite an average body mass loss (p<0.05) of 1.3±0.45 kg during the march. Core temperature rose as a function of marching speed and was unrelated to the % change in body mass. This suggests that changes in mass do not accurately predict changes in TBW (r=-0.16) because either the body mass loss during exercise includes losses other than water or there is an endogenous body water source that is released during exercise not requiring replacement during exercise, or both. Ad libitum water replacement between 65% and 70% of sweat losses maintained safe levels of hydration during the experiment. The finding that TBW was protected by ad libitum drinking despite ∼2% body mass loss suggests that the concept of 'voluntary dehydration' may require revision.
Authors:
Heinrich W Nolte; Timothy D Noakes; Bernard van Vuuren
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Publication Detail:
Type:  Journal Article     Date:  2010-11-03
Journal Detail:
Title:  British journal of sports medicine     Volume:  45     ISSN:  1473-0480     ISO Abbreviation:  Br J Sports Med     Publication Date:  2011 Nov 
Date Detail:
Created Date:  2011-10-12     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0432520     Medline TA:  Br J Sports Med     Country:  England    
Other Details:
Languages:  eng     Pagination:  1106-12     Citation Subset:  IM    
Affiliation:
ERGOnomics TECHnologies, PO Box 6264, Pretoria 0001, South Africa. heinrich@ergotech.co.za.
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