Document Detail

Comparison between blood and urinary fluid balance indices during dehydrating exercise and the subsequent hypohydration when fluid is not restored.
MedLine Citation:
PMID:  22886188     Owner:  NLM     Status:  MEDLINE    
Blood serum osmolality (S (OSM)) is the gold standard to assess body fluid balance. Urine specific gravity (U (SG)) is also a body fluid balance index but it is not invasive. However, U (SG) capability to detect the minimal level of dehydration that affects athletic performance (i.e., 2 %) remains untested. We collected urine and blood samples in eighteen euhydrated trained athletes in the morning and that evening while dehydrating by 1, 2, and 3 % of body mass by cycling (60 % VO₂peak) in the heat (32 °C, 46 % rh, 2.5 m s(-1) air flow). At 9:00 pm, subjects left the laboratory and went to bed after ingesting 0.7 ± 0.2 L of a sports drink. The next morning, subjects awoke 3 % hypohydrated, and blood and urine samples were collected and test terminated. We found that 2 % dehydration increased S (OSM) and U (SG) above exercise-baseline values (P < 0.05). The next morning, S (OSM) and U (SG) remained elevated compared to the first morning while euhydrated (287 ± 5 vs. 282 ± 3 mOsmol kg(-1) H(2)O and 1.028 ± 0.003 vs. 1.017 ± 0.005, respectively, P < 0.05). However, when comparing 3 % dehydration (end of exercise) to 3 % hypohydration (next morning), U (SG) increased (1.025 ± 0.003 to 1.028 ± 0.003; P < 0.05) while S (OSM) decreased (295 ± 5 to 287 ± 5 mOsmol kg(-1) H(2)O; P < 0.05). In summary, during exercise-induced dehydration, U (SG) is as sensitive as S (OSM) to detect low levels of dehydration (i.e., 2 %). Both indices maintain the ability to detect a 3 % overnight hypohydration although S (OSM) approaches euhydration values, while U (SG) remains a superior index to detect hypohydration.
Nassim Hamouti; Juan Del Coso; Ricardo Mora-Rodriguez
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't     Date:  2012-08-11
Journal Detail:
Title:  European journal of applied physiology     Volume:  113     ISSN:  1439-6327     ISO Abbreviation:  Eur. J. Appl. Physiol.     Publication Date:  2013 Mar 
Date Detail:
Created Date:  2013-02-12     Completed Date:  2013-08-23     Revised Date:  2013-09-11    
Medline Journal Info:
Nlm Unique ID:  100954790     Medline TA:  Eur J Appl Physiol     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  611-20     Citation Subset:  IM    
Exercise Physiology Laboratory, University of Castilla-La Mancha, Avda. Carlos III s/n., 45071 Toledo, Spain.
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MeSH Terms
Blood Chemical Analysis
Body Fluids / metabolism,  physiology
Dehydration / blood*,  etiology,  metabolism,  urine*
Electrolytes / analysis,  metabolism
Exercise / physiology*
Health Status Indicators
Sweat / chemistry,  metabolism
Water / metabolism
Water-Electrolyte Balance / physiology*
Water-Electrolyte Imbalance / blood*,  etiology,  urine*
Young Adult
Reg. No./Substance:
0/Electrolytes; 7732-18-5/Water
Comment In:
Eur J Appl Physiol. 2013 Jul;113(7):1907-8   [PMID:  23680939 ]
Eur J Appl Physiol. 2013 Aug;113(8):2167-8   [PMID:  23712213 ]
Eur J Appl Physiol. 2013 Aug;113(8):2169-70   [PMID:  23712214 ]
Eur J Appl Physiol. 2013 Jul;113(7):1905   [PMID:  23680938 ]

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