The effect of warmth acclimation on thermoregulatory behaviour and thermal physiology

Public and commercial buildings tend to overheat and a lot of energy is consumed by air-conditioning and ventilation. However, many occupants remain unsatisfied with the thermal environment. Energy use is significantly influenced by thermoregulatory behaviour (TRB). In the present study, we hypothesize TRB can be affected by warmth acclimation. 12 young healthy men visited the laboratory for 9 consecutive days. TRB was assessed by a so-called SWITCH protocol (90min) before and after acclimation (7days, 6h/day, ~35°C). During SWITCH, participants could freely choose between a warm (37°C) and a cold (17°) condition. TRB was determined by total amount of switches and time spent in a specific condition. Mean skin temperature (14 ISO-defined spots) was measured to indicate behavioural thresholds. After acclimation, the upper critical behaviour threshold (UCBT) of the mean skin temperature significantly increased from 35.17±0.61°C to 35.54±0.47°C (P=0.050). Moreover, the range of mean skin temperatures at which no behaviour occurred (thermoregulatory behaviour neutral zone, TBNZ) significantly widened from 3.63±0.65 to 4.16±0.57 (P=0.027). The total amount of switches tended to decrease (P=0.059). Time spent in the respective conditions remained unchanged. The present study is the first one to show prolonged passive exposure to warmth without exercise extends the behavioural threshold.