Blood volume and protein responses to skin cooling and warming during cycling exercise.

The effects of alterations in mean skin temperature (Tsk) on intravascular volume and protein responses to 90 min of bicycle ergometer exercise have been studied in six male subjects. The onset of exercise was accompanied by an initial rapid haemoconcentration, followed by a slower, progressive haemoconcentration as core and skin temperatures increased. Cooling the skin after 30 min of exercise abolished the slow haemoconcentration, and thereafter, even when Tsk was raised to the pre-exercise level during the final 30 min of exercise, little further change in blood volume was observed. During skin warming, and during recovery from exercise, there was an increase in the total intravascular protein content compared with before exercise. It is concluded that the progressive haemoconcentration often described during cycling exercise may be attributed to an increase in skin blood flow occurring as a result of rises in core and skin temperature, the associated increase in filtration through the cutaneous capillaries causing a progressive loss of plasma volume. The mechanism of the augmentation of intravascular protein remains unclear.