Adaptive changes in physiological and perceptual responses during 10-day heat acclimation training using a water-perfused suit

Yelin Ko,Seon-Hong Seol,Juho Kang,Joo-Young Lee

doi:10.1186/s40101-020-00217-x

Abstract

BackgroundWhile active heat acclimation strategies have been robustly explored, not many studies highlighted passive heat acclimation strategies. Particularly, little evidence demonstrated advantages of utilizing a water-perfused suit as a passive heating strategy. This study aimed to explore heat adaptive changes in physiological and perceptual responses during 10-day heat acclimation training using a water-perfused suit.MethodsNineteen young males were divided into three experimental groups: exercise condition (N = 6, HAEXE, 1-h exercise at 6 km h−1 followed by 1-h rest in a sitting position), exercise and passive heating condition (N = 6, HAEXE+SUIT, 1-h exercise at 6 km h−1 followed 1-h passive heating in a sitting position), and passive heating condition (N = 7, HASUIT, 2-h passive heating in a sitting position). All heating programs were conducted for 10 consecutive days in a climatic chamber maintained at 33 °C with 60% relative humidity. The passive heating was conducted using a newly developed water-perfused suit with 44 °C water.ResultsGreater whole-body sweat rate and alleviated perceptual strain were found in HASUIT and HAEXE+SUIT after 5 and/or 10 days (P < 0.05) but not in the exercise-only condition (HAEXE). Lower rectal temperature and heart rate were found in all conditions after the training (P < 0.05). Heat adaptive changes appeared earlier in HASUIT except for sweat responses.ConclusionsFor heat acclimation in hot humid environments, passive and post-exercise heat acclimation training using the suit (water inflow temperature 44 °C) were more effective than the mild exercise (1-h walking at 6 km h−1). This form of passive heating (HASUIT) may be an especially effective strategy for the elderly and the disabled who are not able to exercise in hot environments.

Highlights

Water-perfused suits have been widely used in thermophysiological studies to form an artificial microclimate on the skin for inducing cold stress [1], heat stress [2], or both [3]
One hour of mild exercise elevated Tre by 1.2 ± 0.2 °Ca for Heat acclimation with exercise (HAEXE) and 1.1 ± 0.2 °Ca for HAEXE+SUIT respectively, while it was increased by 0.5 ± 0.2 °Cb by the passive heating in HASUIT (P < 0.001)
During the second 1 h, Tre decreased by 0.5 ± 0.2 °Cc in HAEXE while taking a seated-rest, it was further elevated by 0.5 ± 0.2 °Cb by post-exercise suit donning in HAEXE+SUIT, and in HASUIT, it achieved 1.0 ± 0.1 °Ca (P < 0.001)

Summary

Introduction

Water-perfused suits have been widely used in thermophysiological studies to form an artificial microclimate on the skin for inducing cold stress [1], heat stress [2], or both [3]. Despite its extensive use in manipulating skin and body core temperatures (Tcore), to the best of our knowledge, there is little research highlighting the potential benefits of utilizing a water-perfused suit as a heat acclimation (HA) strategy. Other studies advocated passive HA strategies, subjecting individuals to heat stress without any exercise mainly by immersion in hot water [11], entering a heat chamber [12], or sauna [13]. These studies suggested that active strategies are not necessary to induce HA as the main stimulus for heat adaptation is a repeated rise in body core temperature [14]. This study aimed to explore heat adaptive changes in physiological and perceptual responses during 10-day heat acclimation training using a water-perfused suit

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