Reduction of submaximal exercise myocardial oxygen demand post-walk training program in coronary patients due to improved physical work efficiency

To assess the effects of walk training on external work efficiency and the determinants of myocardial oxygen demand (MVO₂), we measured total somatic oxygen consumption (VO₂), heart rate (HR), and systolic blood pressure (SBP) in eight male coronary (CAD) patients during submaximal treadmill walking before and after at least 14 weeks of prescribed exercise. Each patient was tested before and after training at the individually determined horizontal treadmill speed that induced ischemic ST segment depression in the pretraining test. Although maximal oxygen uptake (VO₂ max) did not increase significantly with training, submaximal exercise HR and the product of HR and SBP were significantly (p < 0.05) reduced by 10% (120 → 108/min) and 16% (185 × 10² → 156 × 10²), respectively, and none of the patients had ischemic ECG changes after training. The reductions in the cardiac response to exercise were due primarily to a 10% decrease (18.9 → 17.1 ml/kg/min, p < 0.05) in somatic oxygen requirements (VO₂), indicating that the patients became more efficient walkers and reduced their MVO₂ in proportion to the decreased total VO₂. Thus, enhancement of external work efficiency, an extracardiac factor, can lessen myocardial energy costs (MVO₂) and thereby raise the exercise threshold for cardiac ischemia in CAD patients even when aerobic capacity (VO₂ max) is not increased.