ATTENUATION OF THE CUTANEOUS BLOOD-FLOW RESPONSE DURING COMBINED EXERCISE AND HEAT-STRESS

Skin blood flow (SkBF) was measured in six male subjects using laser-Doppler velocimetry, with zero-gradient auditory canal temperature (T-ac) used as an index of body core temperature (T-c). Subjects performed incremental, upright cycling commencing at 40% peak power (W-peak: 10 min), increasing every 4 min by 5% W-peak, thereafter. Trials were conducted in hot (ambient temperature (T-a) 36.7 +/- 0.2 degrees C, relative humidity (rh) 46.1 +/- 3.2%; ($) over bar X +/- S.D.), and neutral environments (T-a 19.6 +/- 0.3 degrees C, rh 50.2 +/- 1.4%). SkBF increased with T-ac in all subjects. Attenuation of SkBF occurred at the same T-ac, relative SkBF and cardiac frequency (f(c)) between environments, but at a lower exercise intensity (40.8 +/- 0.8% versus 55.8 +/- 3.0% W-peak) in the hot environment (p < 0.05). Data indicate that T-c thresholds for SkBF attenuation may exist. However, it is suggested that attenuation thresholds coincided with a reduced central blood volume, which may occur at a critical level of cutaneous blood pooling.