Mitigation of heat strain by wearing a long-sleeve fan-attached jacket in a hot or humid environment.

OBJECTIVES: This study examined whether a fan-attached jacket (FAJ) may mitigate the heat strain in hot or humid environment. METHODS: Nine healthy men engaged in 60-min sessions on a bicycle ergometer (4 metabolic equivalents [METs] workload) in hot-dry (40°C and 30% relative humidity) and warm-humid (30°C and 85% relative humidity) environments. Both are equivalent to an approximately 29°C wet-bulb globe temperature. The experiment was repeated-once wearing an ordinal jacket (control condition) and once wearing a long-sleeve FAJ that transfers ambient air at a flow rate of 12 L/s (FAJ condition)-in both environments. RESULTS: Increases in core temperatures in hot-dry environment were not statistically different between control and FAJ; however, that in the warm-humid environment were significantly different between control and FAJ (0.96 ± 0.10°C and 0.71 ± 0.11°C in rectal temperature, P < .0001; and 0.94 ± 0.09°C and 0.61 ± 0.09°C in esophageal temperature, P < .0001). Changes in heart rate were different between control and FAJ in both environments (62 ± 3 bpm and 47 ± 7 bpm, P < .0001 in hot-dry environment; and 61 ± 3 bpm and 46 ± 5 bpm, P < .0001 in the warm-humid environment) and decrease of %weight change was different in hot-dry environment (1.59 ± 0.12% and 1.25 ± 0.05%, P = .0039), but not in the warm-humid environment. CONCLUSIONS: Wearing a FAJ may mitigate heat strain both in hot or humid environments.