A fan-attached jacket worn in an environment exceeding body temperature suppresses an increase in core temperature

We examined whether blowing hot air above body temperature under work clothing may suppress core temperature. Nine Japanese men engaged in two 30-min bicycle ergometer sessions at a workload of 40% VO₂max at 40 °C and 50% relative humidity. The experiment was conducted without wearing any cooling apparatus (CON), wearing a cooling vest that circulated 10.0 °C water (VEST), and wearing a fan-attached jacket that transferred ambient air underneath the jacket at a rate of 30 L/s (FAN). The VEST and FAN conditions suppressed the increases of rectal temperature (CON, VEST, FAN; 38.01 ± 0.19 °C, 37.72 ± 0.12 °C (p = 0.0076), 37.54 ± 0.19 °C (p = 0.0023), respectively), esophageal temperature (38.22 ± 0.30 °C, 37.55 ± 0.18 °C (p = 0.0039), 37.54 ± 0.21 °C (p = 0.0039), respectively), and heart rate (157.3 ± 9.8 bpm, 136.9 ± 8.9 bpm, (p = 0.0042), 137.5 ± 6.5 bpm (p = 0.0023), respectively). Two conditions also reduced the estimated amount of sweating and improved various subjective evaluations. Even in the 40 °C and 50% relative humidity environment, we may recommend wearing a fan-attached jacket because the heat dissipation through evaporation exceeded the heat convection from the hot ambient air.