Reduction of Physiological Strain Under a Hot and Humid Environment by a Hybrid Cooling Vest

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Abstract
Chan, APC, Yang, Y, Wong, FKW, Yam, MCH, Wong, DP, and Song, W-F. Reduction of physiological strain under a hot and humid environment by a hybrid cooling vest. J Strength Cond Res 33(5): 1429–1436, 2019—Cooling treatment is regarded as one of good practices to provide safe training conditions to athletic trainers in the hot environment. The present study aimed to investigate whether wearing a commercial lightweight and portable hybrid cooling vest that combines air ventilation fans with frozen gel packs was an effective means to reduce participants' body heat strain. In this within-subject repeated measures study, 10 male volunteers participated in 2 heat-stress trials (one with the cooling vest—COOL condition, and another without—CON condition, in a randomized order) inside a climatic chamber with a controlled ambient temperature 33° C and relative humidity (RH) 75% on an experimental day. Each trial included a progressively incremental running test, followed by a 40-minute postexercise recovery. Core temperature (Tc), heart rate (HR), sweat rate (SR), rating of perceived exertion (RPE), exercise duration, running distance, and power output were measured. When comparing the 2 conditions, a nonstatistically significant moderate cooling effect in rate of increase in Tc (0.03 ± 0.02° C·min−1 for COOL vs. 0.04 ± 0.02° C·min−1 for CON, p = 0.054, d = 0.57), HR (3 ± 1 b·min–1·min−1 for COOL vs. 4 ± 1 b·min–1·min−1 for CON, p = 0.229, d = 0.40), and physiological strain index (PSI) (0.20 ± 0.06 unit·min−1 for COOL vs. 0.23 ± 0.06 unit·min−1 for CON, p = 0.072, d = 0.50) was found in the COOL condition during exercise. A nonstatistically significant (p > 0.05) trivial cooling effect (d < 0.2) was observed between the COOL and CON conditions for measures of exercise duration, running distance, power output, SR, and RPE. It is concluded that the use of the hybrid cooling vest achieved a moderate cooling effect in lowering the rate of increase in physiological strain without impeding the performance of progressively incremental exercise in the heat.

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