ANALYSIS OF FACTORS CONCERNED IN MAINTAINING ENERGY BALANCE FOR DRESSED MEN IN EXTREME COLD; EFFECTS OF ACTIVITY ON THE PROTECTIVE VALUE AND COMFORT OF AN ARCTIC UNIFORM
Two men were exposed at 0 [degree]F while dressed in an Army arctic uniform and engaged in controlled activities involving a wide range of energy productions. Measurements of O2 consumption, pulmonary ventilation, body wt. loss, moisture uptake of clothing, and rectal and skin temp. provided information on body energy production, body heat debt, and body energy loss in evaporation of sweat, in evaporation of water from the lungs, in warming the inspired air, in external work, and in radiation and convection through the clothing. The over-all heat economy of 2 subjects was remarkably similar, despite the fact that at any one level of activity the heat losses by sweating were greater for 1 subject while the losses by respiration were greater for the other. The principal adjustment to compensate for alterations in energy production at lower levels of activity was by modification of heat loss by convection, whereas at higher levels of activity it was by sweating. The insulation provided by the clothing was 2.7 clo when the subjects were standing quietly, 1.6 when walking at 2.25 mph., and 1.2 when running at 6 mph. Convection currents set up between the layers of clothing and through the relatively air-impermeable garments under the windbreak layer were considered to be responsible for this decrease in insulation with increasing amplitude and speed of body movement. Predictions regarding the ambient temps. for comfort in this uniform at various grades of activity were verified by the experiences of several subjects.