High-Intensity Interval Training Versus Moderate-Intensity Continuous Training in Older Adults With Heart Failure: A Systematic Review of Comparative Randomized Trials

Abstract

Background: High-intensity interval training (HIIT) has been proposed as a superior alternative to moderate-intensity continuous training (MICT) for improving exercise capacity in patients with heart failure (HF). Early small randomized trials suggested substantial gains in peak oxygen uptake (peak VO₂) and left ventricular ejection fraction (LVEF) with HIIT, but larger multicenter trials have reported neutral findings. Uncertainty persists regarding phenotype-specific effects and clinical relevance in older adults with heart failure. Objective: To systematically evaluate the comparative effects of HIIT versus MICT on exercise capacity and LVEF in older adults with heart failure, and to assess the certainty of evidence across heart failure phenotypes. Methods: A systematic review of randomized controlled trials comparing HIIT and MICT in adults aged ≥60 years with heart failure was conducted in accordance with PRISMA 2020 guidelines. Databases were searched from inception to the final search date without language restriction. Primary outcomes were change in peak VO₂ (mL/kg/min) and LVEF (%). Secondary outcomes included six-minute walk distance (6MWT) and serious adverse events. Random-effects meta-analyses were performed where appropriate. Risk of bias was assessed using the Cochrane RoB 2 tool, and certainty of evidence was evaluated using GRADE. Results: Sixteen comparative randomized studies met inclusion criteria. In heart failure with reduced ejection fraction (HFrEF), pooled meta-analyses demonstrated a modest improvement in peak VO₂ favoring HIIT (mean difference approximately +1.7 to +2.1 mL/kg/min). However, the largest multicenter trial (n=261) showed no significant between-group difference. Pooled improvements in LVEF were small (~3%) and inconsistent across studies. In heart failure with preserved ejection fraction (HFpEF), randomized evidence did not demonstrate superiority of HIIT over MICT, and adjusted analyses suggested exercise volume rather than intensity drove adaptation. Improvements in 6MWT (~28 meters) modestly favored HIIT but approached minimal clinically important thresholds. Serious adverse events were infrequent and comparable between groups under supervised conditions. Certainty of evidence ranged from low (peak VO₂ in HFrEF) to moderate (no important difference in HFpEF; safety outcomes), with downgrading primarily due to inconsistency and small-study effects. Conclusions: In older adults with heart failure, HIIT confers modest improvements in peak VO₂ in HFrEF populations according to pooled analyses, but these advantages are not consistently replicated in large pragmatic multicenter trials and are not observed in HFpEF. Structural improvements in LVEF remain uncertain. Both HIIT and MICT appear safe when delivered under supervision. Exercise prescription should prioritize phenotype-specific considerations, adherence, and sustainability rather than presumed intensity-driven superiority.