Orderly recruitment of thermoeffectors in resting humans

Journal of Applied Physiology

et al. 2019

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We tested the hypothesis that thermal behavior resulting in reductions in mean skin temperature alleviates thermal discomfort and mitigates the rise in core temperature during light-intensity exercise. In a 27 ± 0°C, 48 ± 6% relative humidity environment, 12 healthy subjects (6 men, 6 women) completed 60 min of recumbent cycling. In both trials, subjects wore a water-perfused suit top continually perfusing 34 ± 0°C water. In the behavior trial, subjects maintained their upper body thermally comfortable by pressing a button to perfuse cool water (2.2 ± 0.5°C) through the top for 2 min per button press. Metabolic heat production (control: 404 ± 52 W, behavior: 397 ± 65 W; P = 0.44) was similar between trials. Mean skin temperature was reduced in the behavior trial (by −2.1 ± 1.8°C, P < 0.01) because of voluntary reductions in water-perfused top temperature ( P < 0.01). Whole body ( P = 0.02) and local sweat rates were lower in the behavior trial ( P ≤ 0.05). Absolute core temperature was similar ( P ≥ 0.30); however, the change in core temperature was greater in the behavior trial after 40 min of exercise ( P ≤ 0.03). Partitional calorimetry did not reveal any differences in cumulative heat storage (control: 554 ± 229, behavior: 544 ± 283 kJ; P = 0.90). Thermal behavior alleviated whole body thermal discomfort during exercise (by −1.17 ± 0.40 arbitrary units, P < 0.01). Despite lower evaporative cooling in the behavior trial, similar heat loss was achieved by voluntarily employing convective cooling. Therefore, thermal behavior resulting in large reductions in skin temperature is effective at alleviating thermal discomfort during exercise without affecting whole body heat loss. NEW & NOTEWORTHY This study aimed to determine the effectiveness of thermal behavior in maintaining thermal comfort during exercise by allowing subjects to voluntarily cool their torso and upper limbs with 2°C water throughout a light-intensity exercise protocol. We show that voluntary cooling of the upper body alleviates thermal discomfort while maintaining heat balance through convective rather than evaporative means of heat loss.

Section: Instrumentation and Measurementsmentioning

confidence: 99%

Thermal behavior alleviates thermal discomfort during steady-state exercise without affecting whole body heat loss

Journal of Applied Physiology

et al. 2019

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“…Thermal behavior was measured using a technique modified from those of Cabanac et al [9,23] and currently employed by our laboratory [6,7,11,24]. However, in contrast to previous studies, thermal behavior in the present study involved voluntarily controlling the skin temperature of the torso and arms, a relatively large surface area of the body.…”

Section: Instrumentation and Measurementsmentioning

confidence: 99%

Thermal Behavior Augments Heat Loss Following Low Intensity Exercise

et al. 2019

IJERPH

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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.

“…Thermal behavior was measured using a technique modified by those of Cabanac et al (5,6). This technique requires participants to control the temperature of the dorsal aspect of their neck so that it is thermally comfortable throughout the experiment (2,33,36). The neck is the only skin area known to be equally and highly sensitive to both cooling and heating (26).…”

Section: Instrumentation and Measurementsmentioning

confidence: 99%

Exercise Intensity Independently Modulates Thermal Behavior During Exercise Recovery, But Not During Exercise

Medicine &Amp; Science in Sports &Amp; Exercise

et al. 2019

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We tested the hypothesis that thermal behavior is greater during and following high compared to moderate intensity exercise. In a 27°C, 20% relative humidity environment, participants (10 females) cycled for 30 min at moderate (53±6% VO 2 peak) or high (78±6% VO 2 peak) intensity, followed by 120 min recovery. Mean skin and core temperatures and mean skin wettedness were recorded continuously. Participants maintained thermally comfortable neck temperatures using a custom-made neck device. Neck device temperature provided an index of thermal behavior. The weighted average of mean skin and core temperatures, and mean skin wettedness provided an indication of the afferent stimulus to thermally behave. Mean skin and core temperatures were greater at end-exercise in high intensity (P<0.01). Core temperature remained elevated in high until 70 min recovery (P=0.03). Mean skin wettedness and the afferent stimulus were greater at 10-20 min of exercise in high (P≤0.03), and remained elevated until 60 min recovery (P<0.01). Neck device temperature was lower during exercise in high versus moderate intensity (P≤0.02). There was a strong relation between the afferent stimulus and neck device temperature during exercise (High: R 2 =0.82, P<0.01; Moderate: R 2 =0.95, P<0.01) and recovery (High: R 2 =0.97, P<0.01; Moderate: R 2 =0.93, P<0.01). During exercise, the slope (P=0.49) and y-intercept (P=0.91) did not differ between intensities. In contrast, the slope was steeper (P<0.01) and yintercept was higher (P<0.01) during recovery from high intensity exercise. Thermal behavior is greater during high intensity exercise because of the greater stimulus to behave. The withdrawal of thermal behavior is augmented following high intensity exercise.