Background: Target intensity-level of exercise training in patients with coronary artery disease is adjusted usually by a target heart rate (THR). This THR is aimed to be at or nearby the anaerobic threshold (AT) and is calculated commonly from parameters of regular exercise training, instead of an actual measurement of AT and its related heart rate. Therefore, this study evaluated whether a calculation is reliable.
Methods: In 91 male patients (age 52+/-9 years) exercise capacity was measured after a recent (>4 weeks) coronary event. AT was compared with peak exercise capacity and heart rate at AT was compared with THR, using the Karvonen method.
Results: Mean AT (18.2 ml/min/kg, range 9.2-32.2) and mean peak V(O2) (24.5, range 10.9-43.9) were slightly decreased (respectively 0.83 and 0.79 of predicted). When related to peak exercise capacity, AT showed a large inter-individual variation. For example, heart rate at AT ranged from 0.55 to 0.96 of peak heart rate. As a result heart rate at AT varied considerably with THR. The mean THR, although significantly higher, correlated well with mean heart rate at AT (respectively, 109 and 105/min, P<0.01; r=0.86, P<0.001). However, in an important number of patients heart rate at AT was more than 10% below or above THR (respectively, 30 and 7%).
Conclusion: In individual exercise prescription for cardiac rehabilitation the training level should be determined directly, and not indirectly by calculation from heart rate parameters of exercise testing.