Cardiovascular responses to exhaustive upright cycle exercise in highly trained older men.
It is unclear whether the markedly enhanced aerobic exercise capacity of older endurance-trained men relative to their sedentary age peers is mediated primarily by central or peripheral cardiovascular mechanisms. To address this question, we performed radionuclide ventriculography with respiratory gas exchange measurements during exhaustive upright cycle ergometry in 16 endurance-trained men aged 63 +/- 7 yr and in 35 untrained men of similar age. As expected, maximal O2 consumption during treadmill exercise was much higher in athletes than in controls. At rest and during fixed submaximal cycle work rates through 100 W, athletes demonstrated lower heart rates and greater stroke volume indexes than controls while maintaining similar cardiac indexes and O2 uptake (VO2). At exhaustion, athletes achieved 53% higher work rates and peak VO2 per kilogram body weight than the sedentary men. The higher peak VO2 in athletes was achieved by a 22.5% larger cardiac index and a 15.6% greater arteriovenous O2 difference. The larger peak cardiac index in the athletes than in sedentary controls was mediated entirely by a greater stroke volume index; peak heart rates were virtually identical. The athletes' greater stroke volume index was achieved through an 11% larger end-diastolic volume index and a 7% higher ejection fraction, both of borderline significance. At exhaustion, athletes demonstrated a lower systemic vascular resistance than controls, despite a higher value at rest. Athletes also showed greater exercise-induced increments in heart rate, stroke volume index, and cardiac index and a greater reduction in systemic vascular resistance from rest to maximal workload.(ABSTRACT TRUNCATED AT 250 WORDS)