Concentrations of thrombin-antithrombin III (TAT) complexes in plasma were previously reported to be increased after a 100-km run, while fibrinopeptide A (FPA) concentration remained unchanged. Thus, antithrombin III appears to neutralize thrombin generated during running and prevents fibrin formation. To determine the clinical relevance of these findings, we compared the effects of exhaustive running (1 h, n = 10) on the plasma concentrations of prothrombin fragments F1 and F2, TAT, FPA, and beta-thromboglobulin with the effects of recreational jogging (1 h, n = 10) and exhaustive bicycling on an ergometer (1 h, n = 8). Prothrombin fragments F1 and F2 and TAT concentrations increased significantly in each group. The most significant increase in TAT concentration was measured in the running group (from 1.72 +/- 0.49 to 3.61 +/- 1.03 ng/ml, P < 0.001). The best correlation was found between the postexercise TAT and lactate concentrations (r = 0.62, n = 28, P < 0.001). Mean FPA concentrations after exercise did not exceed normal values in any of the three groups analyzed. An increase in beta-thromboglobulin concentration was measured in the running and in the cycling group. Thus, thrombin is formed, in particular, when associated with anaerobic metabolism, and platelets are activated during high-intensity exercise.