Control of skin blood flow during exercise: thermal and nonthermal factors

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Abstract
Six healthy men exercised on a cycle ergometer at an ambient temperature of 25.degree. C and intensities of 70-100% of their maximal O2 consumption. Subjects alternated 3-4 min of exercise with 2-3 min of recovery. Blood flow was measured in the forearm (ABF) and the finger (FBF) by electrocapacitance plethysmography. Esophageal temperature (Tes) was measured at the level of the left atrium, and mean skin temperature was computed from a weighted average of 8 local temperatures. All subjects had higher ABF at a given Tes during exercise than recovery. Three subjects had lower FBF at a given Tes during exercise and 3 subjects either showed no effect of exercise or had higher FBF during exercise. At the onset of each exercise period all subjects showed a marked reduction in FBF. The reduction was not sustained throughout exercise. ABF showed variable transient changes at the onset of exercise. Because ABF is more representative than FBF of whole-body skin blood flow after an initial transient adjustment, skin blood flow over most of the body at moderate skin temperatures is not lower during exercise than at the same Tes during rest.