Changes in blood viscosity with heavy and light exercise.

To clarify the relationship of the intensity of acute exercise to sudden cardiac death, we examined the effects of short-term heavy and light exercise on whole blood viscosity. Nine healthy sedentary male volunteers performed ten minutes of heavy (more than 95% of maximum oxygen consumption) or light (60% to 65% of maximum oxygen consumption) exercise. Blood samples were obtained before, immediately after, and one hour after exercise. The whole blood viscosity was immediately examined with an oscillation-type viscometer and was found to increase significantly after exercise and subsequently return to baseline levels within one hour after exercise. The whole blood viscosity increased by a similar degree after heavy or light exercise. Therefore, our results suggest that there is a similar risk of sudden cardiac death, due to increased whole blood viscosity, after short-term heavy or light exercise.