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.

Keywords: exercise recovery; thermoregulation; thermoregulatory behavior; voluntary cooling.

Figure 1

Body temperatures (n = 12, mean ± SD). (A) Mean skin temperature, (B) core temperature and (C) time for core temperature to return to pre-exercise levels, during 90 min of recovery from low intensity cycling exercise. ^P Different from pre-exercise (p < 0.03); ^E Different from end-exercise (p < 0.01); * Behavior different from control (p ≤ 0.04); ^# Behavior different from control (p = 0.06).

Figure 2

Skin wettedness, absolute skin humidity, and the saturated vapor pressure at the skin (P_sk,s) (n = 12, mean ± SD). (A) Whole body skin wettedness, (B) under suit top skin wettedness, (C) outside suit top skin wettedness, (D) whole body absolute humidity, (E) under suit top absolute humidity, (F) outside suit top absolute humidity, (G) whole body P_sk,s, (H) under suit top P_sk,s, (I) outside the suit top P_sk,s, during 90 min of recovery from low intensity cycling exercise. ^P Different from pre-exercise (p ≤ 0.04); ^E Different from end-exercise (p ≤ 0.05); * Behavior different from control (p ≤ 0.05).

Figure 3

Thermoeffector responses (n = 12, mean ± SD). (A) Upper body skin temperature; (B) Water perfused top temperature; (C) Forearm skin blood flow; (D) Forearm cutaneous vascular conductance; (E) Local axilla sweat rate; (F) Local thigh sweat rate (n = 6); (G) Cumulative number of button presses, during 90 min of recovery from low intensity cycling exercise. ^P Different from pre-exercise (p ≤ 0.01); ^E Different from 60 min (end-exercise) (p < 0.02); * Behavior different from control (p ≤ 0.05).

Figure 4

Perceptual responses (n = 12, mean ± SD) of (A) upper body thermal sensation, (B) whole body thermal sensation, (C) upper body thermal discomfort, (D) whole body thermal discomfort, (E) Upper body skin wettedness and (F) whole body skin wettedness during recovery from low intensity exercise. ^P Different to pre-exercise (p ≤ 0.05); ^E Different to end-exercise (p < 0.01); * Behavior different from control (p ≤ 0.03).

Figure 5

Dry and evaporative heat loss (n = 12, mean ± SD). (A) Dry heat loss outside the suit top, (B) dry heat loss under the suit top, (C) total dry heat loss, (D) evaporative heat loss outside the suit top, (E) evaporative heat loss under the suit top, (F) total evaporative heat loss during 90 min of recovery from low intensity cycling exercise. ^# Different from 60 min (end-exercise) (p < 0.01); * Behavior different from control (p ≤ 0.05).

Figure 6

(A) Heat storage throughout exercise and recovery, (B) cumulative dry and evaporative heat loss throughout recovery and the sum of (C) cumulative dry and evaporative heat loss during 90 min recovery from low intensity exercise, (n = 12, mean ± SD). ^# Different from 60 min (end-exercise) (p < 0.01); * Behavior different from control (p ≤ 0.02).