Skeletal Muscle and Cardiovascular Adaptations to Exercise Conditioning in Older Coronary Patients

Abstract

Background Older coronary patients suffer from a low functional capacity and high rates of disability. Supervised exercise programs improve aerobic capacity in middle-aged coronary patients by improving both cardiac output and peripheral extraction of oxygen. Physiological adaptations to aerobic conditioning, however, have not been well studied in older coronary patients. Methods and Results The effect of a 3-month and a 1-year program of intense aerobic exercise was studied in 60 older coronary patients (mean age, 68±5 years) beginning 8±5 weeks after myocardial infarction or coronary bypass surgery. Outcome measures included peak aerobic capacity, cardiac output, arteriovenous oxygen difference, hyperemic calf blood flow, and skeletal muscle fiber morphometry, oxidative enzyme activity, and capillarity. Training results were compared with a sedentary, age- and diagnosis-matched control group (n=10). Peak aerobic capacity increased in the intervention group at 3 months and at 1 year by 16% and 20%, respectively (both P <.01). Peak exercise cardiac output, hyperemic calf blood flow, and vascular conductance were unaffected by the conditioning protocol. At 3 and 12 months, arteriovenous oxygen difference at peak exercise was increased in the exercise group but not in control subjects. Histochemical analysis of skeletal muscle documented a 34% increase in capillary density and a 23% increase in succinate dehydrogenase activity after 3 months of conditioning (both P <.02). At 12 months, individual fiber area increased by 29% compared with baseline ( P <.01). Conclusions Older coronary patients successfully improve peak aerobic capacity after 3 and 12 months of supervised aerobic conditioning compared with control subjects. The mechanism of the increase in peak aerobic capacity is associated almost exclusively with peripheral skeletal muscle adaptations, with no discernible improvements in cardiac output or calf blood flow.