Blood hemostasis in exercise and training

Formation of the blood clot is a slow but normal physiological process occu rring as a result of the activation of blood coagulation pathways. Nature's guard against unwanted blood clots is the fibrinolytic enzyme system. In h ealthy people, there is a delicate dynamic balance between blood clot forma tion and blood clot dissolution. Available evidence suggests that exercise and physical training evoke multiple effects on blood hemostasis in normal healthy subjects and in patients. A single bout of exercise is usually asso ciated with a transient increase in blood coagulation as evidenced by a sho rtening of activated partial thromboplastin time (APTT) and increased Facto r Vm (FVIII). The rise in FVIII is intensity dependent and continues into r ecovery. The effects of acute exercise on plasma fibrinogen have yielded co nflicting results. Thus, the issue of whether exercise-induced blood hyperc oagulability in vitro mirrors an in vivo thrombin generation and fibrin for mation remains disputable. Exercise-induced enhancement of fibrinolysis has been repeatedly demonstrated using a wide range of exercise protocols inco rporating various exercise intensities and durations. Moderate exercise app ears to enhance blood fibrinolytic activity without a concomitant activatio n of blood coagulation mechanisms, whereas, very heavy exercise induces sim ultaneous activation of blood fibrinolysis and coagulation. The increase in fibrinolysis is due to a rise in tissue-type plasminogen activator (tPA) a nd decrease in plasminogen activator inhibitor (PAI). The mechanism of exer cise-induced hyperfibrinolysis is poorly understood, and the physiological utility of such activation remains unresolved. Strenuous exercise elicits a transient increase in platelet count, but there are conflicting results co ncerning the effect of exercise on platelet aggregation and activation. Few comprehensive studies exist concerning the influence of exercise training on blood hemostasis, making future investigation necessary to identify whet her there are favorable effects of exercise training on blood coagulation, fibrinolysis, and platelet functions.