Studies on Physiological Responses of Residents in Okinawa to a Hot Environment

Hori, Seiki; Ihzuka, Heikichiro; Nakamura, Masashi

doi:10.2170/jjphysiol.26.235

Cited by 46 publications

(25 citation statements)

References 10 publications

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“…In an area where there is a distinct seasonal fluctuation of ambient temperature, as in Japan, various physiological responses may change season by season. As to sweat responses to seasonal changes during summer, the sweat rate is higher, with a shorter latent period for sweat onset and lower salt concentration in sweat than in winter (Kuno, 1956;Yoshimura, 1960;Hori et al, 1976). In the present study, M sw-back was significantly lower in the MS compared to the JS at rest, and during the exercise and recovery periods, in the well-hydrated condition ( Table 2).…”

Section: Discussionmentioning

confidence: 45%

“…Acclimatization to repeated exposure to heat has been extensively studied. A literature survey revealed a lesser degree of sweating among tropical natives with a lower salt concentration than in temperate natives (Kuno, 1956;Yoshimura, 1960;Hori et al, 1976;Ohwatari et al, 1983;Sasaki and Tsuzuki, 1984;Fan, 1987;Matsumoto et al, 1991Matsumoto et al, , 1993Matsumoto et al, , 1998. Studies on sweat responses to heat load among Japanese (temperate) and Thai (tropical) subjects under identical thermo-neutral conditions showed that Thai subjects had longer sweating onset-time compared to Japanese subjects (Matsumoto et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

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Effects of Exercise in the Heat on Thermoregulation of Japanese and Malaysian Males

Saat

Tochihara

Hashiguchi

et al. 2005

J. Physiol. Anthropol.

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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.

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Section: Discussionmentioning

confidence: 45%

Section: Introductionmentioning

confidence: 99%

Effects of Exercise in the Heat on Thermoregulation of Japanese and Malaysian Males

Saat

Tochihara

Hashiguchi

et al. 2005

J. Physiol. Anthropol.

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“…Many authors have described sweating differences between tropical and nontropical natives (Thomson, 1954;Kuno, 1956;Fox et al, 1974;Hori et al, 1976;Nguyen and Tokura, 2003). It has been suggested that tropical natives have a more efficient thermoregulatory system (Hori, 1995) relying more on dry heat exchange (radiation and convection) because of higher skin temperature and, therefore, requiring less sweat production and evaporation for temperature control.…”

Section: Introductionmentioning

confidence: 99%

Thermoregulatory Efficiency is Increased after Heat Acclimation in Tropical Natives

Magalhães

Passos

Fonseca

et al. 2010

J Physiol Anthropol

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To evaluate the effects of heat acclimation on sweat rate redistribution and thermodynamic parameters, 9 tropical native volunteers were submitted to 11 days of exercise-heat exposures (40Ϯ0°C and 45.1Ϯ0.2% relative humidity). Sudomotor function was evaluated by measuring total and local (forehead, chest, arm, forearm, and thigh) sweat rates, local sweat sodium concentration, and mean skin and rectal temperatures. We also calculated heat production (H), heat storage (S), heat exchange by radiation (R) and by convection (C), evaporated sweat (E sw ), sweating efficiency (h sw ), skin wettedness (w sk ), and the ratio between the heat storage and the sum of heat production and heat gains by radiation and convection (S/(HϩRϩC)). The heat acclimation increased the whole-body sweat rate and reduced the mean skin temperature. There were changes in the local sweat rate patterns: on the arm, forearm, and thigh it increased significantly from day 1 to day 11 (all pϽ0.05) and the sweat rates from the forehead and the chest showed a small nonsignificant increase (pϭ0.34 and 0.17, respectively). The relative increase of local sweat rates on day 11 was not different among the sites; however, when comparing the limbs (arm, forearm, and thigh) with the trunk (forehead and chest), there was a significant higher increase in the limbs (32Ϯ5%) in comparison to the trunk (11Ϯ2%, pϭ0.001). After the heat acclimation period we observed higher w sk and E sw and reduced S/(HϩRϩC), meaning greater thermoregulatory efficiency. The increase in the limb sweat rate, but not the increase in the trunk sweat rate, correlated with the increased w sk , E sw , and reduced S/(HϩRϩC) (pϽ0.05 to all). Altogether, it can be concluded that heat acclimation increased the limbs' sweat rates in tropical natives and that this increase led to increased loss of heat through evaporation of sweat and this higher sweat evaporation was related to higher thermoregulatory efficiency.

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“…A number of studies on thermoregulatory responses to heat exposure with consideration of heat acclimatization level have been reported in terms of physiological adaptations to the thermal environment (Hori et al 1976;Kuno 1956;Matsumoto et al 1993;Nguyen and Tokura 2003;Saat et al 2005;Saat and Tochihara 2008;Taylor 2006). Those investigations reported that residents in tropical areas who were naturally acclimatized to a hot environment respond to heat exposure with a lesser degree of sweating (Fox et al 1974;Hori et al 1976;Lee et al 2004;Matsumoto et al 1991Matsumoto et al , 1993Saat et al 2005) and with a delay in sweating onset time (Fan 1987;Lee et al 2009;Matsumoto et al 1993) than residents of temperate areas.…”

Section: Introductionmentioning

confidence: 99%

“…Those investigations reported that residents in tropical areas who were naturally acclimatized to a hot environment respond to heat exposure with a lesser degree of sweating (Fox et al 1974;Hori et al 1976;Lee et al 2004;Matsumoto et al 1991Matsumoto et al , 1993Saat et al 2005) and with a delay in sweating onset time (Fan 1987;Lee et al 2009;Matsumoto et al 1993) than residents of temperate areas. Reports of lower sweat rate in residents from hot areas do not seem to represent a universal observation following heat acclimatization.…”

Section: Introductionmentioning

confidence: 99%

Comparison of thermoregulatory responses to heat between Malaysian and Japanese males during leg immersion

et al. 2010

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The objective of this study was to investigate thermoregulatory responses to heat in tropical (Malaysian) and temperate (Japanese) natives, during 60 min of passive heating. Ten Japanese (mean ages: 20.8 ± 0.9 years) and ten Malaysian males (mean ages: 22.3 ± 1.6 years) with matched morphological characteristics and physical fitness participated in this study. Passive heating was induced through leg immersion in hot water (42°C) for 60 min under conditions of 28°C air temperature and 50% RH. Local sweat rate on the forehead and thigh were significantly lower in Malaysians during leg immersion, but no significant differences in total sweat rate were observed between Malaysians (86.3 ± 11.8 g m(-2) h(-1)) and Japanese (83.2 ± 6.4 g m(-2) h(-1)) after leg immersion. In addition, Malaysians displayed a smaller rise in rectal temperature (0.3 ± 0.1°C) than Japanese (0.7 ± 0.1°C) during leg immersion, with a greater increase in hand skin temperature. Skin blood flow was significantly lower on the forehead and forearm in Malaysians during leg immersion. No significant different in mean skin temperature during leg immersion was observed between the two groups. These findings indicated that regional differences in body sweating distribution might exist between Malaysians and Japanese during heat exposure, with more uniform distribution of local sweat rate over the whole body among tropical Malaysians. Altogether, Malaysians appear to display enhanced efficiency of thermal sweating and thermoregulatory responses in dissipating heat loss during heat loading. Thermoregulatory differences between tropical and temperate natives in this study can be interpreted as a result of heat adaptations to physiological function.

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Studies on Physiological Responses of Residents in Okinawa to a Hot Environment

Cited by 46 publications

References 10 publications

Effects of Exercise in the Heat on Thermoregulation of Japanese and Malaysian Males

Effects of Exercise in the Heat on Thermoregulation of Japanese and Malaysian Males

Thermoregulatory Efficiency is Increased after Heat Acclimation in Tropical Natives

Comparison of thermoregulatory responses to heat between Malaysian and Japanese males during leg immersion

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