Effects of interval training on work-heat tolerance of young women

COHEN, JUDITH S. and CARL V. GISOLFI. Effects of interval training on work-heat tolerance of young women. Med. Sci. Sports Exercise, Vol. 14, No. 1, pp. 46–52, 1982. The purpose of this study was to determine (a) if women could improve their heat tolerance for more than 2 h of a standard test and (b) the effect of training on heat acclimation (ACCL). Six women (experimental group) ages 19 ± 0.8 yr attempted a standard heat tolerance test (HTT) consisting of a 4-h treadmill walk at 30–35% VO2max in dry heat (45/24°C db/wb, wind velocity 1.22 m/s) before (HTT-I) and after (HTT-II) 11 wk of interval training, and after heat acclimation (HTT-III). A sedentary control group (N=6) matched for age, body weight/surface area, and initial VO2max, performed the same tests but were not trained. ACCL consisted of eight consecutive exposures to the HTT; the eighth exposure served as HTT-III. Training consisted of 90-s treadmill runs at approximately 95% max heart rate (HR) alternated with 60-s rest intervals for 30 min/d (first 2 wk) to 60 min/d (last 9 wk), 4 d/wk in a cool (22°C) environment. Mean rectal temperature (Tre) rose to 39°C, sweat rate (SR) rose to 440 g(m2.h)-1, and VO2max increased 11% (P < 0.05) after the 11-wk interval training program. During HTT-I, the ratio of terminal Tre/tolerance time (used as a measure of heat tolerance) averaged 36.6°C/h for both groups. During HTT-II, this ratio averaged 38 ± 17 and 15 ± 12 for control and experimental groups, respectively; mean performance time was 1.2 ± 0.6 and 3.3 ± 1.3 h, respectively. During HTT-III, five of the six trained subjects, but only one of the six control subjects, achieved thermal equilibrium. Thus, young women who trained in a cool environment for a total of 40 h (spread over 11 wk) were able to (a) work at 30–35% VO2max for more than 3 h in dry heat, and (b) acclimate to the heat in less time than untrained controls.