Marathon run II: Effects on platelet aggregation.

Platelet count and aggregation were assessed in 9 Finnish amateur runners aged 34 to 48, and one 65-year old taking part in a non-competitive marathon race (42.2 km). After the run the mean value of platelet count showed a very significant rise (p less than 0.001). The platelets were markedly more sensitive to both ADP and collagen-induced aggregation. A highly significant increase (p less than 0.001) was noted for both the intensity and velocity of platelet aggregation. The finding of platelet by hyperaggregability after prolonged strenous exercise even in trained subjects is discussed. It is concluded that a through medical examination of the haemostatic balance is recommended before a marathon race.