Exercise and aging: autonomic control of the circulation.

This review describes age-related changes in autonomic control of the circulation during exercise and the associated effects on exercise capacity. The increase in heart rate during exercise becomes smaller with aging probably due to both less withdrawal of cardiac vagal tone and diminished beta-adrenergic responsiveness. The latter also appears to contribute to an attenuation in the left ventricular contractile response to exercise despite greater beta-adrenergic stimulation. At rest, muscle sympathetic nerve activity and arterial plasma norepinephrine spillover rates are elevated in older humans. With aging, sympathetically mediated vasoconstriction in nonactive muscle is augmented during brief dynamic exercise. Paradoxically, during more prolonged exercise increases in plasma norepinephrine concentrations/spillover rates are not greater with age. These age-related changes do not adversely affect submaximal exercise performance at a particular % maximal oxygen consumption. However, the lower peak heart rate and attenuated left ventricular contractile response reduce maximal cardiac output, oxygen consumption, and exercise capacity. In older humans, aerobic exercise training lowers heart rate at rest, reduces levels of heart rate and plasma catecholamines at the same absolute submaximal workload, and, at least in men, improves left ventricular performance during peak exercise, but does not reduce, and may even increase, basal sympathetic nerve activity.