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1 Department of Biomedical Science, University of Wollongong, Wollongong, NSW, Australia
* To whom correspondence should be addressed. E-mail: mark.patterson{at}dsto.defence.gov.au.
We tested the hypothesis that local sweat rates would not display a systematic, post-adaptation redistribution towards the limbs following humid-heat acclimation. Eleven non-adapted males were acclimated over three weeks (16 exposures), cycling 90 min per day, six days a week (40°C, 60% relative humidity), using the controlled-hyperthermia acclimation technique, in which work rate was modified to achieve and maintain a target core temperature (38.5°C). Local sudomotor adaptation (forehead, chest, scapula, forearm, thigh) and onset thresholds were studied during constant work intensity heat stress tests (39.8°C, 59.2% relative humidity) conducted on day 1, 8 and 22 of acclimation. The mean body temperature (Tb) at which sweating commenced (threshold) was reduced on days 8 and 22 (P<0.05), and these displacements paralleled the resting thermoneutral Tb shift, such that the Tb change to elicit sweating remained constant from days 1 to 22. Whole-body sweat rate increased significantly from 0.87 ±0.06 l.h-1, on day 1, to 1.09 ±0.08 and 1.16 ±0.11 l.h-1 on days 8 and 22, respectively. However, not all skin regions exhibited equivalent relative sweat rate elevations from day 1 to 22. The relative increase in forearm sweat rate (117 ±31%) exceeded that at the forehead (47 ±18%; P<0.05) and thigh (42 ±16%; P<0.05), while the chest sweat rate elevation (106 ±29%) also exceeded the thigh (P<0.05). Two unique, post-acclimation observations arose from this project. First, reduced sweat thresholds appeared to be primarily related to a lower resting Tb, and more dependent on Tb change. Second, our data did not support the hypothesis of a generalised and preferential trunk-to-limb sweat redistribution following heat acclimation.
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