Document Detail


Human circulatory and thermoregulatory adaptations with heat acclimation and exercise in a hot, dry environment.
MedLine Citation:
PMID:  8487204     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
1. Heat acclimation was induced in eight subjects by asking them to exercise until exhaustion at 60% of maximum oxygen consumption rate (VO2) for 9-12 consecutive days at an ambient temperature of 40 degrees C, with 10% relative humidity (RH). Five control subjects exercised similarly in a cool environment, 20 degrees C, for 90 min for 9-12 days; of these, three were exposed to exercise at 40 degrees C on the first and last day. 2. Acclimation had occurred as seen by the increased average endurance from 48 min to 80 min, the lower rate of rise in the heart rate (HR) and core temperature and the increased sweating. 3. Cardiac output increased significantly from the first to the final heat exposure from 19.6 to 21.4 l min-1; this was possibly due to an increased plasma volume and stroke volume. 4. The mechanism for the increased plasma volume may be an isosmotic volume expansion caused by influx of protein to the vascular compartment, and a sodium retention induced by a significant increase in aldosterone. 5. The exhaustion coincided with, or was elicited when, core temperature reached 39.7 +/- 0.15 degrees C; with progressing acclimation processes it took progressively longer to reach this level. However, at this point we found no reduction in cardiac output, muscle (leg) blood flow, no changes in substrate utilization or availability, and no recognized accumulated 'fatigue' substances. 6. It is concluded that the high core temperature per se, and not circulatory failure, is the critical factor for the exhaustion during exercise in heat stress.
Authors:
B Nielsen; J R Hales; S Strange; N J Christensen; J Warberg; B Saltin
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The Journal of physiology     Volume:  460     ISSN:  0022-3751     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  1993 Jan 
Date Detail:
Created Date:  1993-06-10     Completed Date:  1993-06-10     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  467-85     Citation Subset:  IM; S    
Affiliation:
August Krogh Institute, University of Copenhagen, Denmark.
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MeSH Terms
Descriptor/Qualifier:
Acclimatization / physiology*
Body Temperature / physiology
Body Temperature Regulation / physiology*
Cardiac Output / physiology
Cardiovascular Physiological Phenomena*
Fatigue / physiopathology*
Heart Rate / physiology
Hot Temperature*
Humans
Male
Physical Exertion / physiology*
Plasma Volume / physiology
Stroke Volume / physiology
Comments/Corrections

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


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