Does exercise training prescription based on estimated heart rate training zones exceed the ventilatory anaerobic threshold in patients with coronary heart disease undergoing usual-care cardiovascular rehabilitation?: A United Kingdom perspective

Abstract

Background: In the United Kingdom (UK), exercise intensity is prescribed from a fixed percentage range (% heart rate reserve; %HRR) in cardiac rehabilitation (CR) programmes. We aimed to determine the accuracy of this approach by comparing it with an objective, threshold-based approach incorporating the accurate determination of ventilatory anaerobic threshold (VAT). We also aimed to investigate the role of baseline cardiorespiratory fitness status, and exercise testing mode dependency (cycle v treadmill ergometer) on these relationships.

Design/Methods: A maximal cardiopulmonary exercise test was conducted on a cycle ergometer or a treadmill before and following usual-care circuit training from two separate CR programmes from a single region in the UK. The heart rate corresponding to VAT was compared to current heart rate-based exercise prescription guidelines. Results: We included 112 referred patients (61 years [59-63]; body mass index 29 kg∙m-2 [29-30]; 88% male). There was a significant but relatively weak correlation (r=0.32; P=0.001) between measured and predicted %HRR, and values were significantly different from each other (P=0.005). Within this cohort, we found that 54% of patients had their VAT identified outside of the 40-70% predicted HRR exercise training zone. In the majority of participants (45%), the VAT occurred at an exercise intensity <40% HRR). Moreover, 57% of patients with low levels of cardiorespiratory achieved VAT at <40% HRR. Whereas, 30% of patients with higher fitness achieved their VAT at >70% HRR. VAT was significantly higher on the treadmill than the cycle ergometer (P<0.001).

Conclusion: In the UK, current guidelines for prescribing exercise intensity are based on a fixed percentage range. Our findings indicate that this approach may be inaccurate in a large proportion of patients undertaking CR.