Activation of blood platelets in response to maximal isometric exercise of the dominant arm

Isometric exercise is a popular form of physical activity for many people. Only few studies exist on the effects of this type of exercise on the hemostatic system. Eleven male healthy subjects (21-42 years) of varying fitness levels were investigated before, immediately after and 10 min after strenuous isometric exercise of the dominant arm. Blood samples were drawn by repetitive puncture from both the exercising and the contralateral arm. The following variables were studied: Prothrombin time and partial thromboplastin time as group tests for the plasmatic coagulation system; platelet count as well as p-selectin expression for the platelet system; tissue plasminogen activator (t-PA) activity and antigen for the fibrinolytic system. The partial thromboplastin time was shortened immediately after maximal isometric exercise of the dominant arm, the prothrombin time remained unchanged. No change was found in the platelet count, but a marked p-selectin expression was observed immediately after maximal isometric exercise of the dominant arm (p < 0.05) and even in the resting contralateral arm. Values returned to baseline after 10 min. There was a slight increase of t-PA antigen concentration and white blood cell count at maximal isometric contraction which did not occur in the resting arm, although changes over the 3 time points were significant in both arms. Maximal isometric exercise leads to platelet activation in both arms, a slight aPTT decrease and t-PA antigen increase in local blood stream. As compensatory fibrinolytic changes do not occur, it is an open question whether isometric exercise increases the potential risk of thromboembolism.