Evaluation of 2 heat-mitigation methods in army trainees

Context: Heat injury is a significant threat to military trainees. Different methods of heat mitigation are in use across military units. Mist fans are 1 of several methods used in the hot and humid climate of Fort Benning, Georgia. Objectives: To determine if (1) the mist fan or the cooling towel effectively lowered participant core temperature in the humid environment found at Fort Benning and (2) the mist fan or the cooling towel presented additional physiologic or safety benefits or detriments when used in this environment. Design: Randomized controlled clinical trial. Setting: Laboratory environmental chamber. Patients or Other Participants: Thirty-five physically active men aged 19 to 35 years. Intervention(s): (1) Mist fan, (2) commercial cooling towel, (3) passive-cooling (no intervention) control. All treatments lasted 20 minutes. Participants ran on a treadmill at 60% VO₂max. Main Outcome Measure(s): Rectal core temperature, heart rate, thermal comfort, perceived temperature, perceived wetness, and blood pressure. Results: Average core temperature increased during 20 minutes of cooling (F_1,28 = 64.76, P <.001, η_p ² = 0.70), regardless of group (F_1,28 = 3.41, P = .08, η_p ² = 0.11) or condition (F_1,28 <1.0). Core temperature, heart rate, and blood pressure did not differ among the 3 conditions. Perceived temperature during 20 minutes of cooling decreased (F_1,30 = 141.19, P <.001, η_p ² = 0.83) regardless of group or condition. Perceived temperature was lower with the mist-fan treatment than with the control treatment (F_1,15=7.38, P=.02, η_p ²=0.32). The mist-fan group perceived themselves to be cooler even at elevated core temperatures. Conclusions: The mist fan and cooling towel were both ineffective at lowering core temperature. Core temperature continued to increase after exercise in all groups. The mist fan produced feelings of coolness while the core temperature remained elevated, possibly increasing the risk of heat illness.