Document Detail


Fitness alters fluid regulatory but not behavioural responses to hypohydrated exercise.
MedLine Citation:
PMID:  18644399     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Dehydration is typical during prolonged exercise. Because training stimulates numerous adaptations, some involving fluid regulation, it is conceivable that training involves adaptations to dehydration. This study tested the hypothesis that trained individuals have altered fluid regulatory, but not behavioural or perceptual responses to exercise when hypohydrated. Six trained (V.O2 peak: 65+/-8 mL kg(-1) min(-1)) and six untrained (V.O2 peak: 45+/-4 mL kg(-1) min(-1)) males cycled for 40 min at 70%V.O2 peak, once whilst euhydrated (EUH) and once whilst hypohydrated by ~2% body mass (HYPO), before a 40-min performance trial with euhydration (in EUH) or ad libitum drinking (in HYPO), in temperate conditions (24.3 degrees C, 50% rh). Baseline hydration was achieved by complete or partial rehydration from exercise+heat stress on the previous evening. Body mass was reduced (-1.8+/-0.1%) and plasma osmolality was increased (5+/-1 mosmol kg(-1)) similarly between fitness groups in HYPO compared to EUH (P<0.05). During exercise, plasma [AVP] rose more in HYPO than EUH; the elevation was greater in the Untrained (4.1+/-1.7 vs. 2.0+/-0.8 pmol L(-1), P<0.01) than Trained (1.4+/-0.6 vs. 1.1+/-0.5 pmol L(-1), P<0.01; P=0.02). Increases in plasma [AVP] relative to osmolality were higher in Untrained than Trained (0.47+/-0.06 vs. 0.025+/-0.05 pmol mosmol(-1), P=0.03). Fitness groups had equivalent thirst ratings during fixed exercise but Trained were thirstier than Untrained when self regulating in HYPO (4.0+/-1.5 vs. 2.7+/-1.2; P=0.05); thus Trained tended to consume more fluid (1.20+/-0.16 vs. 0.88+/-0.16 L; P=0.19), but maintained similar hypohydration consistent with their greater sweat rate during HYPO. In conclusion, aerobic fitness attenuates the neuroendocrine ([AVP]) response to hypohydrated exercise, but not perceptual (thirst) or behavioural (ad libitum drinking) responses.
Authors:
Troy L Merry; Philip N Ainslie; Robert Walker; James D Cotter
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Publication Detail:
Type:  Journal Article; Randomized Controlled Trial; Research Support, Non-U.S. Gov't     Date:  2008-07-02
Journal Detail:
Title:  Physiology & behavior     Volume:  95     ISSN:  0031-9384     ISO Abbreviation:  Physiol. Behav.     Publication Date:  2008 Oct 
Date Detail:
Created Date:  2008-10-17     Completed Date:  2009-02-03     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0151504     Medline TA:  Physiol Behav     Country:  United States    
Other Details:
Languages:  eng     Pagination:  348-52     Citation Subset:  IM    
Affiliation:
School of Physical Education, University of Otago, Dunedin, New Zealand.
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MeSH Terms
Descriptor/Qualifier:
Adult
Analysis of Variance
Arginine Vasopressin / blood
Body Fluids / physiology*
Cross-Over Studies
Dehydration / metabolism*,  physiopathology*
Exercise*
Hemoglobins / metabolism
Humans
Male
Osmolar Concentration
Oxygen Consumption
Physical Fitness*
Sodium / blood
Thirst / physiology
Chemical
Reg. No./Substance:
0/Hemoglobins; 113-79-1/Arginine Vasopressin; 7440-23-5/Sodium

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


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