Thermal Behavior Augments Heat Loss Following Low Intensity Exercise

Abstract

We tested the hypothesis that thermal behavior alleviates thermal discomfort and accelerates core temperature recovery following low intensity exercise. Methods: In a 27 ± 0 °C, 48 ± 6% relative humidity environment, 12 healthy subjects (six females) completed 60 min of exercise followed by 90 min of seated recovery on two occasions. Subjects wore a suit top perfusing 34 ± 0 °C water during exercise. In the control trial, this water continually perfused throughout recovery. In the behavior trial, the upper body was maintained thermally comfortable by pressing a button to receive cool water (3 ± 2 °C) perfusing through the top for 2 min per button press. Results: Physiological variables (core temperature, p ≥ 0.18; mean skin temperature, p = 0.99; skin wettedness, p ≥ 0.09; forearm skin blood flow, p = 0.29 and local axilla sweat rate, p = 0.99) did not differ between trials during exercise. Following exercise, mean skin temperature decreased in the behavior trial in the first 10 min (by −0.5 ± 0.7 °C, p < 0.01) and upper body skin temperature was reduced until 70 min into recovery (by 1.8 ± 1.4 °C, p < 0.05). Core temperature recovered to pre-exercise levels 17 ± 31 min faster (p = 0.02) in the behavior trial. There were no differences in skin blood flow or local sweat rate between conditions during recovery (p ≥ 0.05). Whole-body thermal discomfort was reduced (by −0.4 ± 0.5 a.u.) in the behavior trial compared to the control trial within the first 20 min of recovery (p ≤ 0.02). Thermal behavior via upper body cooling resulted in augmented cumulative heat loss within the first 30 min of recovery (Behavior: 288 ± 92 kJ; Control: 160 ± 44 kJ, p = 0.02). Conclusions: Engaging in thermal behavior that results in large reductions in mean skin temperature following exercise accelerates the recovery of core temperature and alleviates thermal discomfort by promoting heat loss.

Cooling Capacity of Transpulmonary Cooling and Cold-Water Immersion After Exercise-Induced Hyperthermia

“…Furthermore, thermal sensation was less with both the CWI and PB trials than with the PASS trial at postcooling, which is supported by evidence suggesting that reductions in skin temperature after exercise alleviate thermal discomfort. 33,34 Based on the differences in thermal sensation among trials at postcooling that stemmed from afferent feedback of the thermoreceptors on the skin, we speculated that thermal sensation during PB may have been lower throughout cooling than during PASS, despite no difference in cooling rates. The latter could create a scenario in which thermal sensation may be reduced (ie, a sustained elevated internal body temperature), and another bout of physical activity (eg, following thermal rehabilitation in occupational settings, halftime during sport) may increase the risk profile of exertional heat illness.…”

Increased skin wetness independently augments cool‐seeking behaviour during passive heat stress

“…That said, the use of the water-perfused suit is part of this limitation. We know that the water-perfused suit is permeable to water vapour (Vargas et al 2020) and, given that the same water-perfused suit was used in both the low and high skin-wetness trials, it was assumed that the evaporative resistance of the suit was the same between trials. That said, we do not know how water vapour permeability changes with the accumulation of sweat within the fabric of the suit, which likely occurred earlier in the high skin-wetness trial.…”