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

BACKGROUND: While 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. METHODS: Nineteen young males were divided into three experimental groups: exercise condition (N = 6, HA(EXE), 1-h exercise at 6 km h(−1) followed by 1-h rest in a sitting position), exercise and passive heating condition (N = 6, HA(EXE+SUIT), 1-h exercise at 6 km h(−1) followed 1-h passive heating in a sitting position), and passive heating condition (N = 7, HA(SUIT), 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. RESULTS: Greater whole-body sweat rate and alleviated perceptual strain were found in HA(SUIT) and HA(EXE+SUIT) after 5 and/or 10 days (P < 0.05) but not in the exercise-only condition (HA(EXE)). Lower rectal temperature and heart rate were found in all conditions after the training (P < 0.05). Heat adaptive changes appeared earlier in HA(SUIT) except for sweat responses. CONCLUSIONS: For 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 (HA(SUIT)) may be an especially effective strategy for the elderly and the disabled who are not able to exercise in hot environments.