Role of Physical Fitness in Heat Acclimatisation, Decay and Reinduction

Abstract

Loss of heat acclimatisation was investigated, in winter after decay periods of 3, 6, 12 and 18 days, by evaluation or the residual retention and the time necessary for reinduction. Twenty-four fit soldiers (mean [Vdot]o2 max = 49.5 ml kg−1min−1) were concurrently heat acclimatised for 9 days, walking 1.34 ms−1 for 110 min each day at 49°C, 20% R.H., 1.4 ms−1 wind. Physiological measurements included heart rate (HR), rectal temperature (Tre) mean skin temperature (T¯s) and sweat rate. Final mean Tre at 110 min decreased from 39.1°C (day 1) to 38.3°C (day 9). and final moan HR from 160 beats min−1 to 124 boats min−1 (p<.01). An individuals's [Vdot]o2 max was significantly related (r = —0.68) to the number of days for his Tre(. to plateau during acclimatisation. For the decay and reacclimatisation, 4 groups were formed (6 subjects each), homogeneous in [Vdot]o2 max; the moan [Vdot]o2, max for each group was 495±1 ml kg−1 min−1. Initial percent loss of acclimatisation was small (p>0.05) for all groups (3, 6, 12 and 18 days) ranging from group mean losses in Tre of 0-18% and in HK of 2-29%; using Tre and HR criteria, all groups re-acclimatised within 2 days. Their physical fitness is hypothesised as the prime factor in the small decay and rapid reacclimatisation of these subjects even after 18 days.