Metabolic Character of Exercise at Traditional Training Intensities in Cardiac Patients and Healthy Persons

Background Previous studies of heart rate (HR) at anerobic threshold have suggested that target heart rates are insensitive indicators of the metabolic character of exercise prescriptions. Methods This report extended previous work from our laboratory by examining the ventilatory threshold (VT) relative to target heart rates in 11 trained trained healthy persons, 8 trained patients with cardiac disease, and 17 controls (7 untrained healthy persons and 10 untrained cardiac patients). All subjects performed two graded exercise tests to give repeated measures of VT and VO2max with HR responses. Results Ventilatory threshold was highest in trained healthy persons (29.3 ± 4.1 mL/kg/min). Corresponding percentage of HR maximum at VT were 75.0 ± 5% for trained healthy persons, and 72.8 ± 5% for trained healthy persons, and 72.8 ± 5% in untrained cardiac patients. Ventilatory threshodid as a percentage of VO2max averaged 65% among trained cardiac patients, but fell to 56.8 ± 3.8% in untrained healthy persons. Regardless of health or training status, subjects within groups were evenly divided relative to VT at low target within groups were evenly divided relative to VT at low target intensities. At 50$ HR reserve, half the subjects in each group were above VT. Similarly, at 65% VO2max, half were above and half were below VT in each group. Cardiac data from graded exercise testing could not distinguish subjects whose intensity prescription would create training intensities above or below VT because the target heart rate zone varies widely among homogenous subjects regardless of their common health or fitness status. Conclusions Failure to consider ventilatory, metabolic, and cardiac responses to graded exercise testing may result in suboptimal exercise prescriptions. Despite identical target heart rate or percentage of VO2max exercise prescriptions for healthy subjects and patients with cardiac disease may lack uniformity of metabolic character if these factors are not considered. This is an important consideration in the scientific evaluation of physiologic adaptations to training and in devising more specific exercise prescriptions.