Effects of Repeated Bouts of Exercise on the Hemostatic System.

Physical activity is beneficial for health, for example, by lowering the risk of cardiovascular events. However, vigorous exercise is associated with the occurrence of thromboembolic events and sudden cardiac death, in particular in untrained individuals. Whereas acute exercise is known to cause a hypercoagulable state, repeated exposure to (strenuous) exercise by means of training may actually condition the hemostatic response to exercise. To date, the effects of exercise training on blood coagulability and the underlying mechanisms have yet to be fully discerned. In this review, the authors provide an overview of existing literature on how training programs and training status influence hemostasis in healthy individuals. Furthermore, they present data of a pilot study in which we studied the effects of repetitive submaximal intensity cycling on procoagulant and anticoagulant processes. It is known that factor VIII (FVIII) and von Willebrand factor (VWF) increase after exercise, but we found that this increase in FVIII and VWF (antigen, propeptide, and VWF in active conformation) was smaller on each of three subsequent days, suggesting either adaptation of endothelial activation or exhaustion of endothelial VWF supplies. With respect to thrombin generation, elevated FVIII significantly increased the thrombin generation peak but not the endogenous thrombin potential. In contrast, platelet activation in terms of P-selectin expression after stimulation with protease-activated receptor-1 and glycoprotein VI agonists decreased after exercise and did not recover, indicating exhaustion of the platelet response to repetitive exercise.