The Effects of Two Dissimilar Environments with Equivalent Wet Bulb Globe Temperature on Performance of Manual Handling Tasks

Abstract

Wet Bulb Globe Temperature (WBGT) is probably the most widely used of many heat stress indices. An underlying assumption is that differing combinations of temperature and relative humidity which yield the same WBGT will impose the same thermal load. Recent research has cast doubt on this assumption however. The purpose of this study was to investigate the effects of two dissimilar environments with an equivalent WBGT on participants petforming an intermittent box-lifting task. 12 males (mean ± sd), age 25.2 ± 6 yrs, mass 74.9 ± 11.9 kg, stature 1.7 ± 0.1 m were recruited and acclimated over five days (1 hr sessions) in an environmental chamber at 38℃, 70% relative humidity (RH). They completed 6 x 35-min trials on consecutive weekdays in two environments: warm-humid, 30℃, 65% RH (27℃ WBGT); hot-dry, 39℃, 22% RH (27℃ WBGT) and three lift frequencies: 1, 4.3 and 6.7 lifts.min^-1. There were no significant differences in physiological response (heart rate and core temperature), rating of perceived exertion (RPE) and maximum acceptable weight of lift (MAWL) between the two environments. These findings support the underlying assumption of WBGT and contradict recent research. It is possible that differences in response only manifest themselves at higher values of WBGT or during longer bouts of continuous exercise.