AN EVALUATION OF THE ROLE OF SKIN TEMPERATURE DURING HEAT ADAPTATION

This project sought to evaluate the importance of skin temperature dur ing heat acclimation. using an isothermal-strain model. Two groups of seven matched males. participated (1 h per day. 10 days) in one of two conditions: (i) temperate physical training (TEMP: 22.4+/-0.7 degrees C. relative humidity (r.h.) 41.0+/-0.9%): or (ii) combined physical t raining and heat acclimation (HEAT: 38.2+/-0.7 degrees C, r.h. 39.7+/- 1.3%). Isothermal strain was induced in both groups by rapidly elevati ng rectal temperature by 1 degrees C (cycling). then holding it consta nt by manipulating external work. Subjects completed two three-phase h eat stress tests (39.8+/-0.1 degrees C, r.h. 38.6+/-1.2). consisting o f 20 min rest. then 20 min cycling at each of 30% and 45% of peak powe r. before and after each regimen. While there was a difference of 4.2 degrees C in mean skin temperature between treatments. both regimens e licited a similar peripheral sudomotor increase. indicating a core tem perature dependent adaptation. However. based on significant pre- vs. post-acclimation decreases in average auditory canal temperature (0.4/-0.1 degrees C), average forehead skin blood flow (26%). average perc eived exertion (11%). and a 5% increase in average forehead sweat rate (0.1+/-0.04 mg cm(-2) min(-1)). the HEAT regimen elicited a more comp lete acclimation. While elevation in core temperature is critical to a cclimation. it also appears necessary to expose subjects to an externa l thermal stress. This observation has not been previously demonstrate d under conditions of isothermal strain. and verifies the importance o f skin temperature elevation in the acclimation process.