Fall in forearm skin temperature during grade walking on a treadmill

Thermoregulatory responses were observed in 7 male subjects during grade walking at different speeds of between 0.5 and 9 km/hr. The total heat productions (H) in uphill and downhill walking are defined as metabolic heat production (M)--external work (W) and M + W, respectively. During 60 min exercise at 20 degrees C, r. h. 40%, rectal temperature increased to levels dependent on M and independent of H. The sweat-rate varied in proportion to H, and not to M. During 10 min exercise, the environmental conditions (28 degrees C, 40% r.h.) and work intensities were set so that changes in skin temperature could be observed without the interference of sweating. The results indicated that the fall in forearm skin temperature was correlated to M, and not to H. Our previous studies showed that cutaneous vasoconstriction persisted during exercise and that raised work intensities increase the surface area affected by lowered skin temperature. These findings suggest that the rise in core temperature during exercise results from the decreased dry heat loss due to a fall in skin temperature.