Effect of neck versus chest cooling on responses to work in heat.

Six young men performed bench-stepping at a load of 40 W, once at room temperature of 23 degrees C and 3 times in heat (39.5 degrees C db, 30.3 degrees C wb). Two of the heat exposures included cooling of either the neck or chest by circulating cool water having an inlet temperature of 8.3 degrees C. The heat exchanges for the neck and chest were of equal size and they consisted of PVC tubes, having a total length of 3m each, which covered 2.2% of the body surface area. Heat exchange between the tubing assemblies and the environment was prevented by proper insulation. As compared with no cooling in heat, each method of cooling resulted in no change in heart rate, a decrease of 0.5 degrees C in rectal temperature, small and insignificant decreases in skin temperature and 16-22% decreases in sweat rates. Heat removed from the neck and chest equalled 63.1 and61.9 W-m-2, respectively. This large heat removal and the substantial decreases in rectal temperature and sweat rate as a result of cooling 2.2% of the body surface area were explained in terms of the powerful effect of conductive cooling and the particular regions which were cooled.