PLATELET AGGREGABILITY IN RELATION TO THE ANAEROBIC THRESHOLD

Platelet aggregability might be increased during physical exercise. Th is, in turn, has been explained by the elevation of plasma catecholami nes and by the state of lactic acidosis, which occur at high exercise intensities. The purpose of this investigation was to study the relati onship between changes in platelet aggregability and exercise intensit y, the latter being determined in reference to the anaerobic threshold (AT). Each of sixteen male subjects performed an incremental exercise test in order to determine both (a) his running velocity (V-AT) corre sponding to his anaerobic threshold and (b) his running velocity (V-4m M) corresponding to 95% of his running velocity eliciting a blood lact ate concentration of 4 nM.1(-1). Three and six days after this prelimi nary test, respectively, each subject performed an exercise test of 30 minutes, at a constant running velocity of either V-AT or V-4mM. Runn ing velocity for each day's test was randomly assigned. Both capillary and venous blood samples were collected immediately before and immedi ately after each test, and after 30 minutes of recovery from each test , respectively. Capillary blood samples were obtained for determinatio n of blood lactate concentration, whereas venous blood samples were ob tained for determination of platelet count, and platelet aggregation i n response to ADP and collagen, respectively. Platelet count significa ntly increased (p<0.001) immediately after the 30-minutes-tests at eit her V-AT and V-4mM, remaining elevated (p<0.05) after 30 minutes of re covery from the tests at V-4mM. The results did not evidence any signi ficant increase in platelet aggregability with exercise, except for ag gregation response to ADP immediately after the tests performed at V-4 mM (p<0.01). These findings suggest that the exercise-associated incre ase in platelet aggregability is mainly elicited by exercise intensiti es above AT. Accurate determination of AT might therefore be necessary for appropriate exercise prescription in cardiac rehabilitation progr ammes.