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Thermal sensation, a key component of behavioral thermoregulation, is modulated by the changes in both skin and core temperatures. Although cutaneous thermal sensation to local cold is blunted during exercise as compared to rest in normothermic humans, it remains to be determined whether this holds true during core cooling. Furthermore, when local skin thermal sensation is diminished during exercise, it remains unclear whether whole-body thermal sensation is also attenuated. We therefore tested whether low-intensity exercise (VO 2 : ~1300 ml min -1 ) attenuates local skin and/or whole-body thermal sensation in hypothermic young males. Eleven healthy young males (24 ± 2 years) were cooled through cold water immersion (18 °C) up to their lower abdomen while resting (rest trial) and during low-intensity cycling (30-60 W, 30 rpm) (exercise trial). Body temperature, cardiorespiratory variables, and whole-body (9-point scale: 0, unbearably cold; 4, neutral; 8, unbearably hot) and local skin thermal sensation were measured at baseline on land and before the esophageal temperature (T es ) began to decrease (defined as -0.0 T es ) and after 0.5 and 1.0 °C decrements in T es from baseline during the immersion period. Local skin thermal sensation was measured using a thermostimulator with Peltier element that was attached to the chest. The temperature of the probe was initially equilibrated to the chest skin temperature, then gradually decreased at a constant rate (0.1 °C s  - ) until the participants felt coolness. The difference between the initial skin temperature and the local skin temperature that felt cool was assessed as an index of local skin thermal sensation. Throughout the immersions, esophageal and mean skin temperatures did not differ between the rest and exercise trials. Local skin thermal sensation also did not differ between the two trials or at any core temperature level. By contrast, the whole-body thermal sensation score was higher (participants felt less cold) in the exercise than in the rest trial at esophageal temperature of -1.0 °C (1.25 ± 0.46 vs. 0.63 ± 0.35 units, P = 0.035). These results suggest that local skin thermal sensation during low-intensity exercise is not affected by a decrease in core temperature. However, whole-body thermal sensation mediated by a decrease in core temperature (-1.0 °C) is blunted by low-intensity exercise during cold water immersion.1 ) until the participants felt coolness. The difference between the initial skin temperature and the local skin temperature that felt cool was assessed as an index of local skin thermal sensation. Throughout the immersions, esophageal and mean skin temperatures did not differ between the rest and exercise trials. Local skin thermal sensation also did not differ between the two trials or at any core temperature level. By contrast, the whole-body thermal sensation score was higher (participants felt less cold) in the exercise than in the rest trial at esophageal temperature of -1.0 °C (1.25 ± 0.46 vs. 0.63 ± 0.35 units, P = 0.035). These results suggest that local skin thermal sensation during low-intensity exercise is not affected by a decrease in core temperature. However, whole-body thermal sensation mediated by a decrease in core temperature (-1.0 °C) is blunted by low-intensity exercise during cold water immersion., (Copyright © 2021. Published by Elsevier Inc.)

Hypothermia can occur during aquatic exercise despite production of significant amounts of heat by the active muscles. Because the characteristics of human thermoregulatory responses to cold during exercise have not been fully elucidated, we investigated the effect of low-intensity exercise on the shivering response to core cooling in cool water. Eight healthy young men (24 ± 3 yr) were cooled through cool water immersion while resting (rest trial) and during loadless pedaling on a water cycle ergometer (exercise trial). Before the cooling, body temperature was elevated by hot water immersion to clearly detect a core temperature at which shivering initiates. Throughout the cooling period, mean skin temperature remained around the water temperature (25°C) in both trials, whereas esophageal temperature (T es ) did not differ between the trials ( P > 0.05). The T es at which oxygen uptake (V̇o 2 ) rapidly increased, an index of the core temperature threshold for shivering, was lower during exercise than rest (36.2 ± 0.4°C vs. 36.5 ± 0.4°C, P < 0.05). The sensitivity of the shivering response, as indicated by the slope of the T es -V̇o 2 relation, did not differ between the trials (-441.3 ±177.4 ml·min -1 ·°C -1 vs. -411.8 ± 268.1 ml·min -1 ·°C -1 , P > 0.05). The thermal sensation response to core cooling, assessed from the slope and intercept of the regression line relating T es and thermal sensation, did not differ between the trials ( P > 0.05). These results suggest that the core temperature threshold for shivering is delayed during low-intensity exercise in cool water compared with rest although shivering sensitivity is unaffected.

Purpose: This study investigated the effects of water temperature on cardiorespiratory responses and exercise performance during immersed incremental cycle exercise until exhaustion., Methods: Ten healthy young men performed incremental cycle exercise on a water cycle ergometer at water temperatures (T w) of 18, 26 and 34 °C. Workload was initially set at 60 W and was increased by 20 W every 2 min for the first four levels and then by 10 W every minute until the subject could no longer continue., Results: During submaximal exercise (60-120 W), [Formula: see text] was greater at T w = 18 °C than at 26 or 34 °C. Maximal workload was lower at T w = 18 °C than at 26 or 34 °C [T w = 18 °C: 138 ± 16 (SD) W, T w = 26 °C: 157 ± 16 W, T w = 34 °C: 156 ± 18 W], whereas [Formula: see text]O2peak did not differ among the three temperatures [T w = 18 °C: 3156 ± 364 (SD) ml min(-1), T w = 26 °C: 3270 ± 344 ml min(-1), T w = 34 °C: 3281 ± 268 ml min(-1)]. Minute ventilation ([Formula: see text]) and tidal volume (V T) during submaximal exercise were higher at T w = 18 °C than at 26 or 34 °C, while respiratory frequency (f R) did not differ with respect to T w., Conclusion: Peak workload during immersed incremental cycle exercise is lower in cold water (18 °C) due to the higher [Formula: see text] during submaximal exercise, while the greater [Formula: see text] in cold water was due to a larger V T.