Promise and pitfalls of viscoelastic testing for assessing blood hemostasis in ultraendurance sports

Ultraendurance races such as trail ultramarathons push human physiology to extremes, including the blood’s clotting (hemostatic) system. Although regular moderate exercise reduces thrombosis risk and promotes cardiovascular health, extreme efforts tell a more complex story. Events like 50 to 100 km trail runs create a cocktail of dehydration, inflammation, muscle damage, and exertional heat stress—all of which perturb hemostasis. Indeed, thromboembolic events have been documented in otherwise healthy marathoners [1–4].