Thromboembolic events have been reported in marathon athletes during competition. We tested the hypothesis that activation of coagulation and platelets depends on the type of endurance sport and running fraction.

After ethic committee approval, 68 healthy athletes participating in a marathon (MAR, running 42 km, n = 24), a triathlon (TRI, swimming 2.5 km + cycling 90 km + running 21 km, n = 22), and long-distance cycling (CYC, 151 km, n = 22) were included in the study. Blood samples were taken before and immediately after competition. Rotational thrombelastometry was performed (ROTEM; Pentapharm, Germany). The coagulation time (CT) and maximum clot firmness (MCF) after intrinsic activation was assessed. Platelet aggregation was tested using a multiple platelet function analyzer (Multiplate; Dynabyte, Germany) by activation with ADP as well as thrombin-activating peptide 6 and expressed as the area under the curve (AUC). Statistics used the Wilcoxon signed rank test, P < 0.05.

Complete datasets were obtained in 59 athletes (MAR: n = 21, TRI: n = 19, CYC: n = 19). The CT significantly decreased in MAR (from 172 ± 15.3 s to 155 ± 18.3 s), TRI (from 168.1 ± 12.9 s to 154.2 ± 11.3 s), and CYC (from 164.7 ± 17.7 s to 152.5 ± 13.0 s) without differences between groups. In parallel, the MCF increased in all groups (MAR: from 58.1 ± 3.9 mm to 62.4 ± 3.8 mm, TRI: from 56.1 ± 3.2 mm to 59.5 ± 3.1 mm, CYC: from 59.3 ± 5.0 mm to 64.2 ± 4.2 mm). Platelets were only activated during the MAR and TRI, however, as indicated by an increased AUC during TRAP activation in the MAR (from 919 ± 149 to 1,074 ± 290) and an increased AUC during ADP activation in the MAR (from 532 ± 184 to 827 ± 262) and TRI (from 505 ± 205 to 799 ± 329).

As shown before, coagulation is activated during physical activity. We observed significant platelet activation during a marathon and to a lesser extent during a triathlon. We conclude that prolonged running may increase platelet activity. Moreover, we speculate that direct mechanical stress during running contributes to the observed effect. Running therefore activates both coagulation and platelet activity, resulting in an increased risk of thromboembolic incidents in running athletes.