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 waterperfused 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 , 1h 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.

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