Activation of blood platelets in response to maximal isometric exercise ofthe 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 hemos tatic system, Eleven male healthy subjects (21 - 42 years) of varying fitne ss levels were investigated before, immediately after and 10 min after stre nuous isometric exercise of the dominant arm. Blood samples were drawn by r epetitive puncture from both the exercising and the contralateral arm. The following Variables were studied: Prothrombin time and partial thromboplast in time as group tests for the plasmatic coagulation system; platelet count as well as p-selectin expression for the platelet system; tissue plasminog en activator (t-PA) activity and antigen for the fibrinolytic system. The p artial thromboplastin time was shortened immediately after maximal isometri c 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 concentr ation 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 act ivation in both arms, a slight aPTT decrease and t-PA antigen increase in l ocal blood stream. As compensatory fibrinolytic changes do not occur, it is an open question whether isometric exercise increases the potential risk o f thromboembolism.