Hideyuki Tsuneoka

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.

The effect of water-perfused suits and vests on body cooling during exercise in a hot environment

In order to assess different methods of skin surface cooling to reduce exercise-heat stress, this study analyzed the differences in thermoregulatory responses between water-perfused suits (WS) and vests (WV) during exercise in a hot environment. Six male subjects performed three sessions of 20-min cycling at light intensity (250 W/m2) in a room maintained at 28°C (wet-bulb globe temperature, WBGT). The epperiment was performed under seven different conditions, involving three sets of clothing, WS or WV at 14°C (WS14, WV14), 20°C (WS20, WV20) and 26°C (WS26, WV26), and fencing uniforms (FU) only without cooling by water perfusion. In WS conditions, increases in Tes (ΔTes), mean skin temperature (Tsk), heart response (HR), thermal sensation (TS), and total sweat loss (TSL) were significantly (p<0.01) lower in WS14–26 than in FU, while there was no significant difference in the ΔTes between WS14, 20 and 26. In WV conditions, the ΔTes during exercise was similar between WV14, 20 and 26, and these values did not significantly differ from FU. The Tsk was significantly (p<0.01) lower in WV14 and 20 than in FU, and HR, TS and TSL tended to fall in WV14–26 according to the reduced water temperature perfused in the WV. These results show that during light exercise in a hot environment, (1) WS conditions can attenuate an increase in core temperature, and (2) WV conditions can reduce thermoregulatory responses associated with heat stress by lowering the perfused water temperature during exercise in a hot environment.