The influence of habitual exercise on central haemodynamics and peripheral blood pressure regulation in normotensive middle-aged men
Central (aortic) haemodynamics change markedly with age, as aortic stiffness and systolic pressure augmentation increase thereby elevating aortic blood pressure. Furthermore, the autonomic regulation of vascular sympathetic activity also changes; whereby the level of sympathetic nerve activity to the skeletal muscle vasculature, termed muscle sympathetic nerve activity (MSNA), increases, which can elevate peripheral blood pressure. The increase in blood pressure with age increases cardiovascular risk. Notably, exercise training is one recommended strategy to reduce this elevated risk. Although habitual endurance exercise is well known to elicit a range of physiological adaptations, the effects on aortic haemodynamics and peripheral blood pressure regulation are not well described. Therefore, the primary aim of this thesis was to investigate the effects of chronic habitual endurance exercise on aortic (central) haemodynamics and the autonomic regulation and neural control of brachial (peripheral) blood pressure in healthy ageing. To achieve this aim, normotensive middle-aged and young men were recruited into separate groups of chronically endurance-trained runners or recreationally-active nonrunners. Young men were studied to determine the effects of habitual exercise independently of age. Collectively, this thesis shows that in middle-aged men habitual exercise has no significant effects on aortic haemodynamics or the ability of MSNA to effect vascular responses during sympathoexcitation. However, the main finding from this thesis is that habitual endurance exercise, until middle-age, alters the autonomic regulation of MSNA at rest. Specifically, for a similar blood pressure, the arterial baroreflex is set higher in runners, which is associated with a greater likelihood of MSNA burst occurrence. However, there were no between-group differences in young men. Therefore, this greater likelihood of MSNA burst occurrence in middle-aged male runners may represent a fundamental physiological adaptation to chronic (~30 years) habitual endurance exercise to support resting peripheral blood pressure in an expanded cardiovascular system with greater reserve.