Evaluation of a temperate environment test to predict heat tolerance

Summary A temperate environment heat tolerance test (HTT) was formerly reported (Shvartz et al. 1977b) to distinguish heat acclimatized humans from former heat stroke patients. The purpose of this investigation was to evaluate the ability of HTT to measure acute individual changes in the HR and Tre responses of normal subjects, induced by classical heat acclimation procedures, thereby assessing the utility and sensitivity of HTT as a heat tolerance screening procedure. On day 1, 14 healthy males performed HTT (23.2±0.5 ° C db, 14.9±0.5 ° C wb) by bench stepping (30 cm high, 27 steps · min^-1) for 15 min at 67±3% \(\dot V_{O_{2\max } }\). On days 2–9, all subjects underwent heat acclimation (41.2±0.3 ° C db, 28.4±0.3° C wb) via treadmill exercise. Heat acclimation trials (identical on days 2 and 9) resulted in significant decreases in HR (170±3 vs 144±5 beats · min⁻¹), Tre (39.21±0.09 vs 38.56±0.17 ° C), and ratings of perceived exertion; plasma volume expanded 5.2±1.7%. On day 10, subjects repeated HTT; day 1 vs day 10 HR were statistically similar (143±6 vs 137±6 beats · min⁻¹, p>0.05) but Tre decreased significantly (37.7±0.1 vs 37.5±0.1 ° C, p0.05), and individual composite scores indicated that HTT did not accurately measure HR and Tre trends at 41.2 ° C in 6 out of 14 subjects. Among the physical characteristics of subjects, only \(\dot V_{O_{2\max } }\) correlated significantly (r ²=0.74, p<0.001) with HTT, indicating a large aerobic component. We concluded that HTT is not a substitute for classical heat tolerance tests conducted at high ambient temperatures. HTT is apparently most useful in patient or at-risk populations in which preliminary or gross distinctions between heat tolerant and heat intolerant individuals are required.