The aging cardiovascular system: changes in autonomic function at rest and in response to exercise.

Tonic vagal modulation of cardiac period (R-R interval) decreases with advancing age, but is greater in middle-aged and older adults who habitually perform aerobic exercise compared with their sedentary peers. Cardiovagal baroreflex sensitivity also declines markedly with age in sedentary adults but only 50% as much in regularly exercising adults. In previously sedentary middle-aged and older adults, a 3-month program of moderate aerobic exercise increases cardiovagal baroreflex sensitivity by 25%. Tonic (basal) sympathetic nervous system (SNS) activity increases with advancing age in both sedentary and habitually exercising adults. Despite this, SNS beta-adrenergic support of energy metabolism (resting metabolic rate--RMR) declines with age in sedentary individuals. However, SNS beta-adrenergic support of RMR is maintained with age in endurance exercise-trained adults and therefore is much greater in middle-aged and older individuals who exercise regularly compared with their sedentary peers. Thus, regular aerobic (endurance) exercise modulates selective age-associated impairments in autonomic nervous system-physiological function.