Control of thermoregulatory sweating is altered by hydration level
and exercise intensity.
Montain, Scott J., William A. Latzka, and Michael N. Sawka.
Thermal Physiology & Medicine Division, U.S. Army Research
Institute of Environmental Medicine, Natick, MA 01760, Office 508
-651-4564, Fax 508-651-5298
APStracts 2:0253A, 1995.
The purpose of this study was to examine the thermoregulatory sweating
control parameters of threshold temperature and sensitivity to
determine if: 1) these variables were altered by hypohydration level
and exercise intensity; and 2) these alterations, if present, were
additive and independent. Nine heat-acclimated men completed a matrix
of nine trials: three exercise intensities, 25%, 45% and 65% VO2max;
and three hydration levels, euhydration (EU) and hypohydration (HY)
at 3% and 5% of body weight. During each trial, subjects attempted 50
min of treadmill exercise in a warm room (30 degrees C db, 50% rh)
while esophageal temperature and upper arm sweating rate were
continuously measured. Hypohydration was achieved by exercise and
fluid restriction the day preceeding the trials. The following new
findings were made: 1) threshold temperature increased in graded
manner with hypohydration level (0.06 degrees C/%HY); 2) sensitivity
decreased in a graded manner with hypohydration (0.06 units/%HY)
level; 3) threshold temperature was not altered by exercise
intensity; and 4) sensitivity increased from low to moderate and high
intensity exercise. We conclude that both hypohydration level and
exercise intensity produce independent effects on control of
thermoregulatory sweating.
Received 3 February 1995; accepted in final form 6 June 1995.
APS Manuscript Number A131-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.