A comparison of hydration effect on body fluid and temperature regulation between Malaysian and Japanese males exercising at mild dehydration in humid heat.

Hitoshi Wakabayashi,Yutaka Tochihara,Mohamed Saat,Joo-Young Lee,Titis Wijayanto,Nobuko Hashiguchi

doi:10.1186/1880-6805-33-5

Abstract

BackgroundThis study investigated the effect of hydration differences on body fluid and temperature regulation between tropical and temperate indigenes exercising in the heat.MethodsTen Japanese and ten Malaysian males with matched physical characteristics (height, body weight, and peak oxygen consumption) participated in this study. Participants performed exercise for 60 min at 55% peak oxygen uptake followed by a 30-min recovery at 32°C and 70% relative air humidity with hydration (4 times each, 3 mL per kg body weight, 37°C) or without hydration. Rectal temperature, skin temperature, heart rate, skin blood flow, and blood pressure were measured continuously. The percentage of body weight loss and total sweat loss were calculated from body weight measurements. The percentage change in plasma volume was estimated from hemoglobin concentration and hematocrit.ResultsMalaysian participants had a significantly lower rectal temperature, a smaller reduction in plasma volume, and a lower heart rate in the hydrated condition than in the non-hydrated condition at the end of exercise (P <0.05), whereas Japanese participants showed no difference between the two hydration conditions. Hydration induced a greater total sweat loss in both groups (P <0.05), and the percentage of body weight loss in hydrated Malaysians was significantly less than in hydrated Japanese (P <0.05). A significant interaction between groups and hydration conditions was observed for the percentage of mean cutaneous vascular conductance during exercise relative to baseline (P <0.05).ConclusionsThe smaller reduction in plasma volume and percentage body weight loss in hydrated Malaysians indicated an advantage in body fluid regulation. This may enable Malaysians to reserve more blood for circulation and heat dissipation and thereby maintain lower rectal temperatures in a hydrated condition.

Highlights

Introduction and terminologyFederat Proc 1963, 22:930–932. 13
During exercise over a long duration, in hot environments, either hypovolemia or blood distribution to the skin and working muscles can reduce central blood volume [6], which may elicit a decrease in stroke volume and an increase in heart rate compared to a euhydrated condition [1,2,4,5,7,8]
It is difficult to apply the findings observed after short-term heat acclimation to the responses of long-term heat acclimatized populations since the general alteration in sweat response is different in short- and long-term heat adaptation [20,21]

Summary

Introduction

Introduction and terminologyFederat Proc 1963, 22:930–932. 13. Convertino VA, Brock PJ, Keil LC, Bernauer EM, Greenleaf JE: Exercise training-induced hypervolemia: role of plasma albumin, renin, and vasopressin. After short-term heat acclimation, a higher sweat rate is commonly observed [14,18,22,23], whereas a number of studies on longterm heat acclimatization have reported a lower sweat rate among tropical natives compared with temperate natives during heat stress [20,24,25,26]. This reduced sweat response is considered to facilitate the efficiency of plasma preservation, which enables better heat tolerance for body fluid regulation than is the case for temperate natives [20,24,27]. No previous study has clearly compared body fluid regulation or osmoregulation between tropical and temperate indigenes [21]

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Discussion

Conclusion