The effectiveness of various intensity interval training compared to continuous training in patients with heart failure: a systematic review and network meta-analysis

Abstract Background/Introduction Cardiac rehabilitation including exercise therapy is beneficial for improving exercise tolerance, physical function, quality of life (QOL), and life expectancy in patients with heart failure. High-intensity interval training (HIIT) is increasingly reported as a new training modality to improve exercise tolerance more effectively than conventional moderate-intensity continuous aerobic training (MCT). However, the optimal intensity of HIIT for achieving the greatest effects in patients with heart failure remain controversial. Purpose This systematic review and network meta-analysis aimed to examine the effectiveness of HIIT compared to MCT on exercise tolerance in patients with heart failure. Methods We searched for studies published up to 30 January 2024 in Embase, MEDLINE via Ovid SP, PubMed, and the Cochrane Library via Wiley Online Library with no limitations on data, language, or publication status. We included randomised controlled trials comparing the efficacy of HIIT and MCT on peak oxygen uptake (VO2), as a measure of exercise tolerance, aerobic threshold (AT) VO2, ventilatory equivalent of carbon dioxide (VE/VCO2) slope, and QOL. We categorized HIIT into three different intensities [> 80% heart rate max (HRM), 60-80% HRM, < 60% HRM] and compared the outcomes with those of MCT. Results We identified 15 randomised controlled trials with 557 patients from a total of 27,931 records. Our network meta-analysis revealed that the following results of peak VO2 from the comparisons among the three intensities of HIIT and MCT: > 80% HRM (10 studies, mean difference 1.27 ml/min/kg, 95% confidence interval -0.20 to 2.73), 60-80% HRM (3 studies, 1.47, -0.89 to 3.83), < 60% HRM (2 studies, 2.10, -1.22 to 5.43) (Fig. 1). Regarding AT VO2, HIIT at 60-80% HRM demonstrated significant improvements compared to MCT: > 80% HRM (8 studies, 0.18, -0.83 to 1.18), 60-80% HRM (2 studies, 2.50, 0.72 to 4.28), < 60% HRM (2 studies, 1.14, -0.93 to 3.20) (Fig. 2). Regarding VE/VCO2 slope, HIIT at 60-80% HRM also demonstrated significant improvements compared to MCT: > 80% HRM (7 studies, 0.29, -1.89 to 2.47), 60-80% HRM (2 studies, -3.26, -6.18 to -0.35), < 60% HRM (no study). The network meta-analysis did not reveal any significant differences in QOL between the various intensities of HIIT and MCT. Conclusions Our systematic review and network meta-analysis revealed that HIIT prescribed at a sub-maximal intensity, 60-80% heart rate max, is most effective in improving exercise tolerance. Higher intensity does not necessarily yield better outcomes, and future research on interval training should include detailed methodologies that account for the training intensity.Fig.1 Network meta-analysis on peak VO2Fig.2 Network meta-analysis on AT VO2