Lack of Insulating Effect of Body Fat During Exposure to Internal and External Heat Loads

¹ From the Department of Physiology, School of Medicine, and the Department of Physical Education, University of North Carolina, Chapel Hill, North Carolina

Changes in heart rate, skin and rectal temperatures and rates of sweating were measured in 14 normal and 14 obese subjects under the following test situations: 1) 90 minutes' resting exposure to heat (48–50°C, 20–30% relative humidity), 2) 45 minutes' exercise in the heat, at 3 miles per hour, zero grade and 3) 60 minutes' exercise at 25°, 4 miles per hour, 10% grade. Equivalent rectal temperature changes in the normal and obese subjects indicated the lack of significant insulating effect of subcutaneous fat in heat stresses of brief duration. Equivalent heart rate changes indicated approximately equal cardiovascular stress in the two groups of subjects. It is concluded that any inferiority in the performance of obese subjects in the heat would be due a) to the greater metabolic cost of work and b) to slower recovery dissipation of heat load resulting from their lower ratio of surface area to body weight.