Abstract
Seasonal heat acclimatization is known to enhance autonomic thermoeffector responses, whereas the behavioural response following seasonal heat acclimatization remains unknown. We investigated whether seasonal heat acclimatization would alter autonomic and behavioural thermoregulatory responses. Sixteen healthy participants (eight males and eight females) underwent two trials involving 50 min of lower‐leg passive heating (lower‐leg submersion in 42°C water) with (Fan trial) and without (No fan trial) the voluntary use of a fan in a moderate thermal environment (27°C, 50% relative humidity) across winter and summer months. In Fan trials, participants were allowed to use a fan to maintain thermal comfort, but this was not allowed in the No fan trials. Cool‐seeking behaviour was initiated at a lower change in rectal temperature [mean (SD): 0.21 (0.18)°C vs. 0.11 (0.13)°C, P = 0.0327] and change in mean skin temperature [2.34 (0.56)°C vs. 1.81 (0.32)°C, P < 0.0001], and cooling time was longer [16.46 (5.62) vs. 20.40 (4.87) min, P = 0.0224] in summer compared with winter. However, thermal perception was not modified by season during lower‐leg passive heating (all P > 0.0864). Furthermore, rectal temperature was higher in summer ( P = 0.0433), whereas mean body temperature and skin temperature were not different (all P > 0.0631) between the two seasons in Fan trials. In conclusion, seasonal heat acclimatization enhanced the cool‐seeking behaviour from winter to summer.
What is the central question of this study? Repeated heat exposure during the summer months (seasonal heat acclimatization) can enhance autonomic thermoregulatory responses in humans, but does it also modify cool‐seeking behaviour during passive heat exposure? What is the main finding and its importance? Although seasonal heat acclimatization enhanced cool‐seeking behaviour in young adults during lower‐leg passive heating, it was initiated earlier, more frequently in the summer compared with the winter. These adaptations indicate that thermal behaviour might complement the autonomic thermoregulatory response.