Effects of exercise intensity on clot microstructure and mechanical properties in healthy individuals

Background Exercise is well established to lead to exercise-induced hypercoagulability, as demonstrated by kinetic coagulation markers. It remains unclear as to whether exercise-induces changes lead in clot development and increased polymerisation. Fractal dimension (d_f) has been shown to act as a marker of clot microstructure and mechanical properties, and may provide a more meaningful method of determining the relationship between exercise-induced hypercoagulability and potential clot development. Methods d_f was measured in 24 healthy individuals prior to, after 5 min of submaximal exercise, following maximal exercise, 45 min of passive recovery and following 60 min of recovery. Results were compared with conventional markers of coagulation, fibrinolysis and SEM images. Results Significantly increased d_f was observed following exercise, returning to resting values following 60 min of recovery. The relationship between d_f and mature clot microstructure was confirmed by SEM: higher d_f was associated with dense clots formed of smaller fibrin fibres immediately following exercise compared to at rest. Conventional markers of coagulation confirmed findings of previous studies. Conclusion This study demonstrates that d_f is a sensitive technique which quantifies the structure and properties of blood clots following exercise. In healthy individuals, the haemostatic balance between coagulation and fibrinolysis is maintained in equilibrium following exercise. In individuals with underlying vascular damage who participate in exercise, this equilibrium may be displaced and lead to enhanced clot formation and a prothrombotic state. d_f may therefore have the potential to not only quantify hypercoagulability, but may also be useful in screening these individuals.