Intravascular volume and protein responses to running exercise.

The roles of posture and mean skin temperature (Tsk) in determining intravascular volume and protein responses to running exercise were examined in 12 male subjects. Moving from a sitting to a standing position before exercise was always accompanied by a decrease in blood volume (BV), as indicated by increases in the hematocrit and hemoglobin concentration. Although neither the onset of running nor alterations in Tsk during running caused any further consistent change in BV, there was an acceleration of the rate at which protein entered the intravascular space. At the end of exercise and in recovery this led to an augmentation of intravascular protein. It is concluded that intravascular volume responses to running exercise are determined by the accompanying postural hemoconcentration, and that running per se and any imposed thermal stress have minimal effects on BV thereafter. A hypothesis is presented which accounts for the reportedly diverse effects of different forms of exercise on BV in terms of the posture-dependent BV being obtained immediately before exercise begins.