Effects of immersion precooling on human performance during and after warm-water exercise.

摘要

Human performance in warm water is limited relative to performance in air environments. Naval Special Warfare (NSW) personnel are often tasked with in-water operations in thermally stressful environments. Warm-water diving operations have become a concern for NSW as modern theaters of conflict include bodies of water that can reach temperatures well above 34°C or 93.2°F (e.g., Persian Gulf). Factors of extended dive duration, garments that impair heat dissipation and strenuous workloads can compound the effects of heat stress in warm water and have an adverse impact on health, personnel safety, and mission performance. Precooling has been shown to extend work performance in hot, humid air environments. Precooling prior to warm-water immersion may alleviate some of the problems associated with thermal stress in warm water by increasing an individual's capacity to store heat and decreasing the thermal strain induced by exercise. The objective of this research was to evaluate whole-body, head-out precooling in cold water as a method to increase performance during and after 30 minutes of strenuous exercise in 36.6°C (97.8°F) water. Participants served as their own controls. Specific objectives were to determine if (a) whole-body precooling prior to exercise in warm water results in a greater overall work output in a defined time period, (b) cumulative heat storage during exercise in warm water is reduced by whole-body precooling, and (c) physical and cognitive performance following warm-water exercise are improved by whole-body precooling. Participants (n=11) underwent precooling and control phases, followed by 30 minutes of strenuous exercise in warm water, and then completed physical and cognitive test batteries. Body temperature was monitored continuously. Total work output, changes in body temperature, heat storage, physical performance, cognitive performance, and blood lactate levels were used to measure the effect of precooling. Precooling had minimal impact on functional performance, although heat storage capacity and sustained hand grip measures were significantly enhanced. Results suggest the precooling profile used in this study would not significantly extend work times or increase safety for work performed in warm water. Active cooling while in warm water may be a better research approach to extend safety and duration in warm water.