Effects of exercise in the heat on thermoregulation of Japanese and Malaysian males

Mohamed Saat, Yutaka Tochihara, Nobuko Hashiguchi, Roland Gamini Sirisinghe, Mizuho Fujita, Chin Mei Chou

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36 Citations (Scopus)

Abstract

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: poorly-hydrated (no water was given) and well-hydrated (3 mL·Kg -1 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: 31.6±0.03°C, rh: 72.3±0.13%). 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 (1.43 ±0.08%) compared to MS (1.15±0.05%). 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 well-hydrated 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.

Original languageEnglish
Pages (from-to)267-275
Number of pages9
JournalJournal of physiological anthropology and applied human science
Volume24
Issue number4
DOIs
Publication statusPublished - Jul 1 2005

All Science Journal Classification (ASJC) codes

  • Social Sciences(all)

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