Elsevier

Heart, Lung and Circulation

Volume 24, Issue 2, February 2015, Pages 149-157
Heart, Lung and Circulation

Original Article
Interval Training Versus Continuous Exercise in Patients with Coronary Artery Disease: A Meta-Analysis

https://doi.org/10.1016/j.hlc.2014.09.001Get rights and content

Background

High aerobic capacity is inversely related to cardiovascular disease morbidity and mortality. Recent studies suggest greater improvements in aerobic capacity with high-intensity interval training (interval) compared to moderate-intensity continuous aerobic exercise (continuous). Therefore we perform a meta-analysis of randomised controlled trials comparing the effectiveness of INTERVAL versus CONTINUOUS in aerobic capacity, amongst patients with stable coronary artery disease (CAD) and preserved ejection fraction

Methods

We searched PubMed, EMBASE, CINAHL, the Australia and New Zealand Clinical Trials Register, clinicaltrials.gov and TROVE for randomised controlled trials comparing INTERVAL with CONTINUOUS in patients with CAD. Studies published in the English language up to December 2013 were eligible for inclusion. Aerobic capacity, quantified by peak oxygen consumption (VO2peak) post exercise training was extracted and compared post-intervention between INTERVAL and CONTINUOUS by way of a fixed model meta-analysis. Secondary outcomes including anaerobic threshold, blood pressure and high-density lipoproteins (HDL) were also analysed.

Results

Six independent studies with 229 patients (n = 99 randomised to INTERVAL) were included in the meta-analysis. There was a significantly higher increase in VO2peak following INTERVAL compared to CONTINUOUS (Weighted Mean Difference = 1.53 ml•kg−1min−1, 95% CI 0.84 to 2.23) with homogeneity displayed between studies (Chi Squared = 2.69; P = 0.7). Significant effects of INTERVAL compared to CONTINUOUS were also found for anaerobic threshold but not systolic blood pressure.

Conclusion

In patients with CAD, INTERVAL appears more effective than CONTINUOUS for the improvement of aerobic capacity in patients with CAD. However, long-term studies assessing morbidity and mortality following INTERVAL are required before this approach can be more widely adopted.

Introduction

Exercise-based cardiac rehabilitation is an effective strategy for reducing total and cardiovascular mortality in patients with coronary artery disease (CAD) [1]. Furthermore, aerobic fitness has been established as a strong predictor of cardiovascular [2], [3] and all-cause mortality [4]. Defining aerobic fitness by way of cardiopulmonary exercise testing has become increasingly available in many rehabilitation settings, where peak oxygen consumption (VO2peak) can be directly measured as the gold standard for aerobic capacity. Increases in VO2peak have been shown to relate to improvements in mortality risk [5], where every 1-metabolic equivalent (1-MET = 3.5 ml•kg−1min−1 VO2) increase yields a 13% improvement in survival. Exercise training-induced increases in aerobic capacity are therefore highly desirable for the improvement of patient outcomes.

Optimising exercise rehabilitation to maximise the potential increase in aerobic capacity is an important factor in the prescription of exercise. In patients with CAD, traditional exercise prescription has included continuous aerobic exercise, such as walking or cycling, at a moderate intensity (40-80% VO2peak) for 30-60 minutes [6]. However, recent evidence in healthy participants [7], [8], heart failure patients [9], [10] and patients with cardiometabolic disease [11] suggests that high-intensity interval training (INTERVAL) may be a more effective strategy for the improvement of aerobic capacity than continuous, moderate intensity exercise training (CONTINUOUS).

High-intensity interval training is characterised by brief intermittent bursts of exercise interspersed by active recovery periods, and has shown a number of benefits in patients with CAD, including improvements in aerobic capacity, anaerobic threshold, endothelial function and cardiac function [9], [12].

Studies comparing INTERVAL with CONTINUOUS training in patients with heart disease typically prescribe intervals of up to four minutes duration at an intensity of approximately 85-95% peak heart rate (HRpeak) [9], [13], [14]. Alternatively, shorter durations of one to two minutes have also been applied with a 1:1 work:rest ratio [15], [16]. Likewise, both shorter [7] and longer intervals [8] have been shown to increase aerobic capacity compared to CONTINUOUS in healthy participants.

In many instances, the benefits on aerobic capacity of INTERVAL appear to exceed the improvements seen with CONTINUOUS training. Previous meta-analyses of studies recruiting heart failure [10] and cardiometabolic disease patients [11] indicate that INTERVAL results in increases of approximately 2-3 ml/kg/min VO2peak greater than that observed with CONTINUOUS training.

Previous systematic reviews have included studies comparing INTERVAL with no exercise [17] or patients with metabolic and/or other lifestyle diseases in addition to those with CAD [11]. More recently, a meta-analysis revealed greater improvements in aerobic capacity with INTERVAL compared with CONTINUOUS in patients with CAD [18]. However, since publication of this meta-analysis, a further study has been published comparing the two approaches. Importantly, the meta-analysis by Pattyn et al, included studies in which patients had ischaemic heart failure and ejection fractions <40% [9]. Additionally, in some studies analysed, there were no differences in the actual exercise intensity between the two training methods. The aim of the present study was to perform a meta-analysis of all randomised controlled trials studies comparing the effectiveness of INTERVAL with CONTINUOUS on aerobic capacity, defined using VO2peak, amongst patients diagnosed with stable CAD in the absence of disclosed heart failure.

Section snippets

Study Selection

The search aimed to find both published and unpublished studies. The search was restricted to studies published in the English language prior to December 2013. A three-step search strategy was employed; an initial limited search of PubMed and CINAHL was undertaken followed by analysis of text words contained in the title and abstract, and of the index terms used to describe the article. A second search using all identified keywords and index terms was then undertaken across PubMed, EMBASE,

Identified Studies

Following the initial search, 5553 studies were reviewed by their title and abstract (Fig. 1). Of these, 39 were retrieved in full-text, 32 of which did not match the eligibility criteria for the study. Following assessment of methodological quality, eight articles were included in the meta-analysis. In two instances, two articles were reporting outcomes from the same study [12], [13], [19], [20]. In these instances, both articles were treated as a single study such that the final analysis

Discussion

The findings of this meta-analysis indicate that INTERVAL is more effective than CONTINUOUS for the improvement of both VO2peak and the anaerobic threshold in patients with stable CAD in the absence of heart failure. The greater improvement in VO2peak following INTERVAL compared to CONTINUOUS (4.6 ± 3.1 versus 2.8 ± 2.4 ml•kg−1min−1) is important in the context of a 10-25% survival advantage with every 3.5 ml•kg−1min−1 improvement in VO2peak [23]. These findings are in agreement with previous

Acknowledgements

No financial assistance was provided for this study. The authors wish to thank Dr Matthew Stephenson for assistance in the preparation of this analysis.

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