Platelet activation, including the formation of monocyte platelet aggregates (MPAs), contributes to atherosclerosis, thrombus formation, and acute coronary syndromes. Regular participation in exercise can lower cardiovascular risk, but little is known regarding the impact of exercise training on platelet function. We investigated the effect of 6 mo of walking exercise on platelet function in sedentary older adults without significant cardiovascular disease. Twenty-seven participants were randomly allocated to 6 mo of either: no-exercise (n = 13) or 3x50 min/wk of supervised center-based walking (n = 14). Circulating and agonist-induced MPAs were assessed using flow cytometry before (month 0 (0M)) and after (month 6 (6M)) the intervention. Circulating MPAs increased from 0M (3.7 +/- 1.0%) to 6M (4.7 +/- 1.6%) in the no-exercise group (p = 0.009), whereas a nonsignificant decrease was observed in the walking group (0M 4.3 +/- 1.7 versus 6M 3.7 +/- 1.2%, p = 0.052). The change in MPAs between groups was significant (p = 0.001). There were no differences between groups in platelet responses to agonists across the interventions (all p > 0.05). Collectively, these data suggest that the absence of regular exercise may increase MPAs, which are cellular mediators involved in atherosclerosis, while regular walking inhibits such increases. The thrombotic function of platelets appears to be relatively unaltered by exercise training. This study provides novel data related to the cardioprotective effects associated with participation in exercise.

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