What is the effect of aerobic exercise intensity on cardiorespiratory fitness in those undergoing cardiac rehabilitation? A systematic review with meta-analysis

Objective Assess the role of exercise intensity on changes in cardiorespiratory fitness (CRF) in patients with cardiac conditions attending exercise-based cardiac rehabilitation. Design Systematic review with meta-analysis. Data sources MEDLINE, Embase, CINAHL, SPORTDiscus, PsycINFO and Web of Science. Eligibility criteria for selection Studies assessing change in CRF (reported as peak oxygen uptake; (V) over dotO(2peak)) in patients post myocardial infarction and revascularisation, following exercise-based cardiac rehabilitation. Studies establishing (V) over dotO(2peak) via symptom-limited exercise test with ventilatory gas analysis and reported intensity of exercise during rehabilitation were included. Studies with mean ejection fraction <40% were excluded. Results 128 studies including 13 220 patients were included. Interventions were classified as moderate, moderate-to-vigorous or vigorous intensity based on published recommendations. Moderate and moderateto-vigorous-intensity interventions were associated with a moderate increase in relative (V) over dotO(2peak) (standardised mean difference +/- 95% CI=0.94 +/- 0.30 and 0.93 +/- 0.17, respectively), and vigorous-intensity exercise with a large increase (1.10 +/- 0.25). Moderate and vigorous-intensity interventions were associated with moderate improvements in absolute (V) over dotO(2peak) (0.63 +/- 0.34 and 0.93 +/- 0.20, respectively), whereas moderate-to-vigorous-intensity interventions elicited a large effect (1.27 +/- 0.75). Large heterogeneity among studies was observed for all analyses. Subgroup analyses yielded statistically significant, but inconsistent, improvements in CRF. Conclusion Engagement in exercise-based cardiac rehabilitation was associated with significant improvements in both absolute and relative (V) over dotO(2peak). Although exercise of vigorous intensity produced the greatest pooled effect for change in relative (V) over dotO(2peak), differences in pooled effects between intensities could not be considered clinically meaningful.