Attenuation of cardiovascular adaptations to exercise in frail octogenarians

To determine the mechanisms underlying increased aerobic power in response to exercise training in octogenarians, we studied mildly frail elderly men and women randomly assigned to an exercise group (n = 22) who participated in a training program of 6 mo of physical therapy, strength training, and walking followed by 3 mo of more intense endurance exercise at 78% of peak heart rate or a control sedentary group (n = 24). Peak O₂ consumption (V̇O_{2 peak}) increased 14% in the exercise group (P < 0.0001) but decreased slightly in controls. Training induced 14% increase (P = 0.027) in peak exercise cardiac output (Q̇), determined via acetylene rebreathing, and no change in arteriovenous O₂ content difference. The increase in Q̇ was mediated by increases in heart rate (P = 0.009) and probably stroke volume (P = 0.096). Left ventricular stroke work also increased significantly. In the men, the increase in V̇O_{2 peak} was exclusively due to a large increase in peak Q̇ (22%). In the women, the gain in V̇O₂ peak was due to small increases in Q̇ and O ₂ extraction from skeletal muscles. Pulse pressure normalized for stroke volume and arterial elastance during peak effort did not change with training. Controls showed no changes. The results suggest that, although frail octogenarians have a diminished capacity for improvement in aerobic power in response to exercise training, this adaptation is mediated mostly by an increase in Q̇ during peak effort. Furthermore, Q̇ likely plays a greater role in the adaptive increase in V̇O_{2 peak} in old men than old women.