A novel approach to characterize the energy cost of human cool-seeking behavior and its individual variability during heat stress

Behavioral 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 behaviors in humans has been rarely quantified. Here, we present a novel approach to characterize the energy cost of a common human cool-seeking behavior (i.e., manual fanning) and its individual variability during heat stress. Ten healthy males (20 ± 1 yr) participated in two 60-min trials (CONTROL and FAN) consisting of resting exposure to 37(±0.4)°C and 44(±6)% relative humidity (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 (T_c), mean skin temperature ([Formula: see text]), forehead T_sk, microclimate (next-to-skin) relative humidity ([Formula: see text]), heart rate (HR), and thermal discomfort during both trials, and used FAN accelerometery data to characterize cool-seeking behavior's onset, duration, bout frequency, and work rate. Seven participants engaged with self-fanning, which varied individually in onset time [mean: 12:30 min:s (range: 00:49-30:19)], total duration [05:54 min:s (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; <i>P</i> = 0.993), nor time-dependent changes in T_c, [Formula: see text], [Formula: see text], and HR. Our results indicate that our novel approach, which combines 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, behaviorally mediated thermoregulatory actions and their individual variability during heat stress.<b>NEW & NOTEWORTHY</b> We present a novel approach to characterize the energy cost of a common human cool-seeking behavior (i.e., manual fanning) and its individual variability during heat stress. Results indicate that our novel approach, which combine accelerometery (movement patterns) and indirect calorimetry (energy expenditure), is feasible and effective. This approach could be applied to a variety of thermal behaviors, thereby broadening the methodological toolkit available to researchers to study the relationship between behavioral and autonomic human thermoregulation.