Effect of glucose-water ingestion on exercise thermoregulation in men dehydrated after water immersion
Dearborn, A.S.; Ertl, A.C.; Jackson, C.G.; Barnes, P.R.; Breckler, J.L.; Greenleaf, J.E.; Greenleaf, J.E.
Aviation Space and Environmental Medicine 70(1): 35-41
1999
ISSN/ISBN: 0095-6562 PMID: 9895019 Document Number: 503971
Background: The influence of non-ionic osmols on thermoregulation is unclear. Hypothesis: Hyperglycemia will attenuate the rise in exercise core temperature. Methods: Dehydrated by 4-h of water immersion (34.5degreeC) to the neck, 6 men, (35 +- SD 7 yr) participated in each of three trials where 2.0 gcntdotkg-1 body wt of oral glucose (33.8% weight per volume) was consumed followed by 80 min supine rest (Glu/Rest), or 70 min supine cycle exercise at 62.8% +- SE 0.5% (1.97 +- 0.02 Lcntdotmin-1) peak O2 uptake, followed by 10 min supine recovery with prior (Glu/Ex) or without glucose (No Glu/Ex) ingestion. Blood samples were taken periodically for measurement of Hb, Hct, Na+, K+, Osm, and glucose; mean skin (Tsk) and rectal (Tre) temperatures, and sweating rate (resistance hygrometry) and skin blood velocity (laser Doppler) were measured intermittently. Results: Mean percent changes in plasma volume (p < 0.05) for the exercise trials were not different: - 1 2.3 +- 2.2% (No Glu/Ex) and -12.1 +- 2.1%(Glu/Ex). Mean (+-SE) pre-exercise plasma (glucose) for Glu/Ex was higher than that of No Glu/Ex (1 08.4 +- 3.9 vs. 85.6 +- 1.6 mgcntdotdL-1, respectively, p < 0.05). Glu/Ex vs. No Glu/Ex data, respectively, at the end of exercise indicated that: Tre was lower by 0.4degreeC (38.2 +- 0.2 vs. 38.6 +- 0.1degreeC, p < 0.05), Tsk was lower (32.0 +- 0.3 vs. 32.4 +- 0.2degreeC, p < 0.05), forearm sweating rate was lower (0.94 +- 0.09 vs. 1.05 +- 0.07 mgcntdotcm-2cntdotmin-1, p < 0.05); and head (temporal) skin blood velocity was not different (1.67 +- 0.21 vs. 1.51 +- 0.24 Hzcntdot103, NS). Conclusions: Elevation of plasma (glucose) prior to supine submaximal exercise in dehydrated men attenuates the increase of Tre without alteration of heat production, total body sweating, serum electrolytes and osmolality, or exercise-induced hypoglycemia: the mechanism may be enhanced peripheral blood flow that could enhance body heat loss.
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