Masashi Kume

Determination of the Optimum Muscle Temperature for Maintaining Work Performance with Attenuation of Heat Stress in Human

The purpose of this study was to investigate the optimum muscle temperature required to maintain work performance with attenuation of heat stress. Nine male subjects (23±0.36 year) performed eight 8-sec bouts of maximal cycling exercise at a load intensity of 60% of their peak power output, with a 40-sec resting period between bouts, in a room maintained at 24.8±0.2°C and 52±1% relative humidity. The subjects worn trousers lined with tubes perfused water at 6°C, 17°C, 30°C or 44°C, and the target thigh muscle temperatures were 32°C (32.4±0.2°C), 34°C (34.4±0.2°C), 36°C (36.3±0.1°C) and 38°C (37.5±0.2°C), respectively. The peak power output from first to fourth bouts and the total work output during eight bouts were significantly greater at the 36°C and 38°C conditions than at the 32°C and 34°C conditions (p<;0.01), while there were no remarkable differences between the 36°C and 38°C conditions. After 10 minutes of the eight bouts of exercise, the tympanic temperature (Tty) was significantly elevated at the 38°C condition, but fell at the 32°C and 34°C conditions compared to that at baseline (p <; 0.01), while the Tty remained constant at the 36°C condition. The heart rate and rating of perceived exertion during eight bouts and the total sweat loss from the start to the end of experiment were significantly greater for the 38°C condition than for the 32°C and 34°C conditions. These results suggest that thigh temperature of approximately 36°C may be optimal to maintain repeated maximal cycling exercise performance with the attenuation of heat stress.

Effects of Lower Limb Cooling on the Work Performance and Physiological Responses During Maximal Endurance Exercise in Humans

The purpose of this study was to investigate the effects of lower limb cooling on the work performance and physiological responses during maximal endurance exercise in humans. Eight male subjects underwent a maximal aerobic test using graded exercise on a cycle ergometer. The subjects wore trousers lined with tubes perfused water at 6 or 32 °C, and the target thigh muscle temperatures were 32 or 36 °C, respectively. The maximal working time was significantly lower during 32 °C than under 36 °C conditions. However, the body temperature, heat storage, heart rate and the total sweat loss were significantly lower under the 32 °C condition compared to those under the 36 °C condition. These results suggest that cooling the lower limbs to reach a thigh temperature of approximately 32 °C can reduce the physiological strain during maximal endurance exercise, although the endurance work performance under the 32 °C condition is lower than that under the 36 °C thigh temperature condition.

The effect of starting or stopping skin cooling on the thermoregulatory responses during leg exercise in humans.

To assess the effects of starting or stopping leg cooling on the thermoregulatory responses during exercise, 60 min of cycling exercise at 30% of maximal oxygen uptake was performed under 4 conditions using tube trouser perfused with water at 10 °C; no leg cooling (NC), starting of leg cooling after 30 min of exercise (delayed cooling, DC), continuous leg cooling (CC), and stopping of continuous leg cooling after 30 min of exercise (SC) at an environmental temperature of 28.5 °C. During exercise under the DC conditions, an instantaneous increase in the esophageal temperature (Tes), a suppression of the cutaneous vascular conductance at the forearm (%CVC), and a decrease in the mean skin temperature (Tsk) were observed after leg cooling. The total sweat loss (Δm sw,tot) was lower under the DC than the NC condition. In the SC study, however, the Tes remained constant, while the %CVC increased gradually after leg cooling was stopped, and the Δm sw,tot was greater than that under the CC condition. These results suggest that during exercise, rapid skin cooling of the leg may cause an increase in core temperature, while also enhancing thermal stress. However, stopping skin cooling did not significantly affect the core temperature long-term, because the skin blood flow and sweat rate subsequently increased.