Effect of Exercise Intensity on Active Rewarming From Outdoor Cold-Water Immersion

Introduction Cold-water immersion (CWI) is a threat to warfighters operating in the cold. Even after removal from the cold, core temperature continues to decrease because of the afterdrop effect. The purpose of this study is to evaluate the effect of exercise-intensity on rewarming from CWI. Materials and Methods Following a randomized match-paired design, 28 military personnel (27 Male, 1 Female; mean ± SD age: 29 ± 7year; ht: 175 ± 11 cm; wt: 86.9 ± 12.5 kg; body fat: 22 ± 9%) were immersed in an outdoor pond (air: −4.2 °C; water: 1.3 °C) for 10 minutes and subsequently rewarmed for 40 minutes by following a low-intensity [LI (n = 14); 30% VO2R] or moderate-intensity [MI (n = 14); 45% VO2R] exercise protocol. Core temperature, hand temperature, foot temperature, and heart rate were recorded throughout. Physiological responses were analyzed in 5-minute increments using a 2 (condition) by 11 (time) repeated measures analysis of variance (ANOVA) with significance set to P < .05. Results After 20 minutes of exercise, heart rate was significantly higher in the MI group relative to the LI group (P < .05). Core temperature (F = 34.0, P < .001, ηp2 = 0.630), hand temperature (F = 114.9, P < .001, ηp2 = 0.839), and foot temperature (F = 128.8, P < .001, ηp2 = 0.896) were all significantly different across time points; however, there was no main effect of group or group by time interaction effects. Conclusions Results suggest that rewarming of the core, hands, and feet following CWI were similar between LI and MI groups. Moderate-intensity exercise did not exacerbate the afterdrop effect. When rewarming after CWI, the Warfighter can select a low-to-moderate exercise intensity that best fits their comfort and mission requirements.