Energy Requirements of Men in Extreme Heat

A study was performed in extreme heat on 8 healthy young adults for three consecutive 10-day periods. In period 1 daytime temperatures in the hot sun averaged 40.5°C, in period 2 in the hot shade, 40.3°C, and in period 3 in the cool shade 26.0°C. The men carried on constant daily activity, and were allowed food and water ad libitum. 1.With the set conditions of this study, the data suggest that there is an increased caloric requirement for men working and living in extreme heat. Significant increases were observed in food consumption and the actual caloric requirements were even greater because of changes in the body composition of the men.2.The differences in energy cost of the various resting and exercise activities, when comparing the hot-sun or hot-shade to the cool-shade phase were significant.3.Energy requirements averaged 55.5, 56.4 and 36.6 Cal. per kg of body weight, when corrected for body composition changes.4.These increased requirements are probably due to the increased heat load imposed on the body by solar radiation and extreme heat. The increased requirements are, in all likelihood, a combination of increased action of the blood in heat transport, increased action of the sweat glands, plus the increased total metabolic rate due to the evaluation in body temperature.