Adaptation to Heat.

Hori, Seiki

doi:10.2170/jjphysiol.45.921

Cited by 94 publications

(70 citation statements)

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“…It has already been shown that tropical natives are more efficient thermoregulators as they rely less on sweat production and evaporation for heat dissipation than nontropical natives (Hori, 1995;Saat et al, 2005a). Evidence of the partial state of adaptation of the subjects of the present study is the nonsignificant change in resting rectal temperature after HA.…”

Section: Discussionsupporting

confidence: 50%

“…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. Nguyen and Tokura (2003) showed that Vietnamese had a higher oscillation in internal temperature in comparison to Japanese, what could lead to less sweat production.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionsupporting

confidence: 50%

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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“…Tropical inhabitants possessed heattolerance due to enhanced dry heat loss such as radiation, convection and conduction, which was convenient for maintaining body fluid and osmolarity (Matsumoto et al, 1993(Matsumoto et al, , 1997. According to Hori (1995) the higher T sk for subjects born in Okinawa (subtropical) may be due to the result of an increased blood volume with improvement in the cutaneous circulation and reduction in the subcutaneous fat level induced by long-term HA. Residents of temperate zones have been reported to show a decrease in T sk after HA (Aoyagi et al, 1997).…”

Section: Discussionmentioning

confidence: 99%

Effects of Short-term Exercise in the Heat on Thermoregulation, Blood Parameters, Sweat Secretion and Sweat Composition of Tropic-dwelling Subjects

Saat

Sirisinghe

Singh

et al. 2005

J. Physiol. Anthropol.

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This study investigates the effects of a shortterm aerobic training program in a hot environment on thermoregulation, blood parameters, sweat secretion and composition in tropic-dwellers who have been exposed to passive heat. Sixteen healthy Malaysian-Malay male volunteers underwent heat acclimation (HA) by exercising on a bicycle ergometer at 60% ofVO 2 max for 60 min each day in a hot environment (Ta: 31.1Ϯ0.1°C, rh: 70.0Ϯ4.4%) for 14 days. All parameters mentioned above were recorded on Day 1 and at the end of HA (Day 16). On these two days, subjects rested for 10 min, then cycled at 60% of V O 2 max for 60 min and rested again for 20 min (recovery) in an improvised heat chamber. Rectal temperature (T re ), mean skin temperature (T sk ) heart rate (HR), ratings of perceived exertion (RPE), thermal sensation (TS), local sweat rate and percent dehydration were recorded during the test. Sweat concentration was analysed for sodium [Na ϩ ] sweat and potassium. Blood samples were analysed for biochemical changes, electrolytes and hematologic indices. Urine samples were collected before and after each test and analysed for electrolytes.After the period of acclimation the percent dehydration during exercise significantly increased from 1.77Ϯ0.09% (Day 1) to 2.14Ϯ0.07% (Day 16). Resting levels of hemoglobin, hematocrit and red blood cells decreased significantly while [Na ϩ ] sweat increased significantly. For T re and T sk there were no differences at rest. T re , HR, RPE, TS, plasma lactate concentration, hemoglobin and hematocrit at the 40th min of exercise were significantly lower after the period of acclimation but mean corpuscular hemoglobin and serum osmolality were significantly higher while no difference was seen in [Na ϩ ] sweat and T sk . It can be concluded that tropicdwelling subjects, although exposed to prolonged passive heat exposure, were not fully heat acclimatized. To achieve further HA, they should gradually expose themselves to exercise-heat stress in a hot environment.

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“…Heat acclimation is transient and gradually disappears if not maintained by continued or repeated heat exposures. In the permanent residents of the tropical zone, basal metabolic rate (or basal heat production) is lower than those in more temperate zones 61) .…”

Section: Improvements Of Thermoregulationmentioning

confidence: 90%

Heat Illness during Working and Preventive Considerations from Body Fluid Homeostasis

Kamijo

Nosé

2006

Ind Health

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The purposes of this review are to show pathophysiological mechanisms for heat illness during working in a hot environment and accordingly provide some preventive considerations from a viewpoint of body fluid homeostasis. The incidence of the heat illness is closely associated with body temperature regulation, which is much affected by body fluid state in humans. Heat generated by contracting muscles during working increases body temperature, which, in a feedback manner, drives heat-dissipation mechanisms of skin blood flow and sweating to prevent a rise in body temperature. However, the impairment of heat-dissipation mechanisms caused by hard work in hot, humid, and dehydrated conditions accelerates the increase in body temperature, and, if not properly treated, leads to heat illness. First, we overviewed thermoregulation during working (exercising) in a hot environment, describe the effects of dehydration on skin blood flow and sweating, and then explained how they contributes to the progression toward heat illness. Second, we described the advantageous effects of blood volume expansion after heat acclimatization on temperature regulation during exercise as well as those of restitution from dehydration by supplementation of carbohydrate-electrolyte solution. Finally, we described that the deteriorated thermoregulation in the elderly is closely associated with the impaired body fluid regulation and that blood volume expansion by exercise training with protein supplementation improves thermoregulation.

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Adaptation to Heat.

Cited by 94 publications

References 0 publications

Thermoregulatory Efficiency is Increased after Heat Acclimation in Tropical Natives

Thermoregulatory Efficiency is Increased after Heat Acclimation in Tropical Natives

Effects of Short-term Exercise in the Heat on Thermoregulation, Blood Parameters, Sweat Secretion and Sweat Composition of Tropic-dwelling Subjects

Heat Illness during Working and Preventive Considerations from Body Fluid Homeostasis

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