Koch Esteves, N., Luck, D., Blount, H., Cavallo, F.R., Worsley, P.R., Sheffield, J., Galea, I. and Filingeri, D. (2026) A novel approach to characterize the energy cost of human cool-seeking behavior and its individual variability during heat stress. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 330 (2), R232-R242. (doi:10.1152/ajpregu.00271.2025).
Abstract
Behavioural thermoregulation (e.g. cool-seeking) is thought to proceed autonomic heat-loss responses (e.g. sweating), due to energy-conservation requirements. However, the energy cost of cool-seeking behaviours in humans has been rarely quantified. Here we present a novel approach to characterise the energy cost of a common human cool-seeking behaviour (i.e. manual fanning) and its individual variability during heat stress. Ten healthy males (20±1y) participated in two 60-min trials (CONTROL and FAN) consisting of resting exposure to 37(±0.4)°C and 44(±6)% RH. During FAN, participants freely used a hand-held fan instrumented with an accelerometer, to offset thermal discomfort. During CONTROL, no fan was provided. We measured energy expenditure (breath-by-breath gas analysis), core temperature (Tc), mean skin temperature (Tsk), forehead Tsk, microclimate (next-to-skin) relative humidity (RHsk), heart rate (HR), and thermal discomfort during both trials; and used FAN accelerometery data to characterise cool-seeking behaviour’s onset, duration, bout frequency, and work rate. Seven participants engaged with self-fanning, which varied individually in onset time (mean: 12:30 mm:ss [range: 00:49-30:19]), total duration (05:54 mm:ss [01:04-17:53]), and bouts (6 [1-17]), but not work rate (308±51 strokes·min-1). Energy expenditure did not differ between FAN vs. CONTROL in those who fanned (433±28 vs. 447±64 KJ; p=0.993), nor time-dependent changes in Tc, Tsk, RHsk, and HR. Our results indicate that our novel approach, which combine accelerometery (to quantify movement patterns) and indirect calorimetry (to measure associated energy expenditure), is both feasible and effective in quantifying the energetic cost of voluntary, behaviourally mediated thermoregulatory actions, and their individual variability during heat stress.
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