The effect of low-intensity exercise in the heat on thermoregulation and certain biochemical changes in temperate and tropical subjects under poorly and well-hydrated states was examined. Two VO 2max matched groups of subjects consisting of 8 Japanese (JS) and 8 Malaysians (MS) participated in this study under two conditions: poorlyhydrated (no water was given) and well-hydrated (3 mL · Kg Ϫ1 body weight of water was provided at onset of exercise, and the 15th, 35th and 55th min of exercise). The experimental room in both countries was adjusted to a constant level (Ta: 31.6Ϯ0.03°C, rh: 72.3Ϯ0.13%). Subjects spent an initial 10 min rest, 60 min of cycling at 40% VO 2max and then 40 min recovery in the experimental room. Rectal temperatures (T re ) skin temperatures (T sk ), heart rate (HR), heat-activated sweat glands density (HASG), local sweat rate (M sw-back ) and percent dehydration were recorded during the test. Blood samples were analysed for plasma glucose and lactate levels.The extent of dehydration was significantly higher in the combined groups of JS (1.43Ϯ0.08%) compared to MS (1.15Ϯ0.05%). During exercise M sw-back was significantly higher in JS compared to MS in the well-hydrated condition. The HASG was significantly more in JS compared to MS at rest and recovery. T re was higher in MS during the test. T sk was significantly higher starting at the 5th min of exercise until the end of the recovery period in MS compared to JS.In conclusion, tropical natives have lower M sw-back associated with higher T sk and T re during the rest, exercise and recovery periods. However, temperate natives have higher M sw-back and lower T sk and T re during experiments in a hot environment. This phenomenon occurs in both poorly-hydrated and wellhydrated states with low intensity exercise. The differences in M sw-back , T sk and T re are probably due to a setting of the core temperature at a higher level and enhancement of dry heat loss, which occurred during passive heat exposure.

This study investigated the differences in heat dissipation response to intense heat stress during exercise in hot and humid environments between tropical and temperate indigenes with matched physical characteristics. Ten Japanese (JP) and ten Malaysian (MY) males participated in this study. Subjects performed exercise for 60 min at 55% peak oxygen uptake in 32°C air with 70% relative humidity, followed by 30 min recovery. The increase in rectal temperature (T(re)) was smaller in MY during exercise compared to JP. The local sweat rate and total body mass loss were similar in both groups. Both skin blood flow and mean skin temperature was lower in MY compared to JP. A significantly greater increase in hand skin temperature was observed in MY during exercise, which is attributable to heat loss due to the greater surface area to mass ratio and large number of arteriovenous anastomoses. Also, the smaller increase in T(re) in MY may be explained by the presence of a significantly greater core-skin temperature gradient in MY than JP. The thermal gradient is also a major factor in increasing the convective heat transfer from core to skin as well as skin blood flow. It is concluded that the greater core-skin temperature gradient observed in MY is responsible for the smaller increase in T(re).

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