The effects of exercise and exercise conditioning on blood platelet function were investigated in six healthy individuals who had not engaged in regular exercise for at least 1 yr prior to the study. The subjects (three men and three women) had a mean age of 28 (range 23-32) and participated in a supervised program of treadmill exercise. Subjects exercised for 20 min, three times weekly, for 12 wk at 70-80% of estimated maximum heart rate. Samples for platelet counts, platelet aggregation, and plasma [beta]-thromboglobulin ([beta]-TG) were obtained prior to training and after 6 and 12 wk of training. All subjects responded with an increase in aerobic capacity during training. Resting mean systolic and diastolic blood pressures decreased after training (P < 0.05). Platelet counts increased after exercise, and the increment in week 12 exceeded that in the 1st wk by 57%. Platelet aggregation studies in platelet rich plasma (PRP) showed an increase in slope after exercise (week 1, P < 0.05) which decreased with training (week 1 vs week 12, P < 0.01). Aggregation studies utilizing impedance aggregometry in diluted native whole blood showed an acceleration of both spontaneous aggregation (P < 0.01 weeks 6 and 12) and aggregation using epinephrine as an agonist (P < 0.05) following exercise. Plasma [beta]-TG levels did not increase significantly after exercise; however, resting concentrations of [beta]-TG decreased with training (P < 0.03). These data support the conclusion that platelet counts increase and platelet aggregation is accelerated by exercise but that platelet responsiveness decreases with exercise training.
(C)1990The American College of Sports Medicine