Exercise Training Rewires Heart Failure Biology From Muscle to Molecule

Heart failure affects millions worldwide and carries substantial morbidity and mortality despite advances in pharmacological therapy. Exercise intolerance is a hallmark symptom, yet paradoxically, structured exercise training has emerged as a powerful non-pharmacological intervention. Clinical guidelines broadly recommend it, but the mechanistic underpinnings and optimal prescription parameters remain incompletely defined. This 2025 review in Circulation Research by Mounsey, Guo, Lau, and Ho provides a thorough synthesis of both clinical outcomes and biological mechanisms.

On the clinical side, the review examines landmark and contemporary trials across HF subtypes. In HF with reduced ejection fraction (HFrEF), trials such as HF-ACTION demonstrated that aerobic exercise training modestly but meaningfully reduces cardiovascular mortality and hospitalization when adjusted for prognostic covariates, while consistently improving peak VO₂ and health-related quality of life. Evidence in HF with preserved ejection fraction (HFpEF) — a population historically underrepresented in exercise trials — shows robust improvements in exercise capacity and functional status, though mortality benefits remain less established. The review highlights the importance of exercise modality, including continuous moderate-intensity aerobic training, high-intensity interval training (HIIT), and resistance training, each with distinct physiological targets.

Mechanistically, the authors trace adaptations along the entire oxygen transport chain. At the cardiac level, exercise training can promote reverse remodeling, reduce left ventricular filling pressures, and improve diastolic function. Pulmonary adaptations include improved ventilatory efficiency and reduced exercise-induced pulmonary hypertension. Peripheral vascular effects encompass enhanced endothelial function, increased nitric oxide bioavailability, and improved arterial compliance. Skeletal muscle adaptations — including mitochondrial biogenesis, fiber-type shifts toward oxidative phenotypes, and improved oxygen extraction — are highlighted as particularly important contributors to symptom relief and functional gains.

The review also examines systemic and molecular mechanisms. Exercise training attenuates chronic low-grade inflammation characteristic of HF by reducing pro-inflammatory cytokines (e.g., TNF-α, IL-6) and modulating immune cell phenotypes. Antioxidative effects include upregulation of endogenous antioxidant enzymes, reducing oxidative stress that contributes to myocardial and vascular injury. Neurohormonal benefits include attenuation of sympathetic nervous system overactivation and renin-angiotensin-aldosterone system dysregulation. Emerging data on inter-organ crosstalk — including exercise-induced myokines, cardiokines, and metabolic mediators — point to a coordinated systemic response that extends benefits beyond any single organ.

The authors acknowledge important caveats and future directions. Much of the mechanistic evidence derives from animal models or small human studies, and translation to diverse HF populations remains incomplete. Optimal exercise dose, modality, and timing relative to HF therapies require further investigation. Personalized exercise prescription informed by biomarkers, imaging, or genetic profiles represents a promising frontier. Overall, this review reinforces exercise training as a cornerstone of HF management with multilayered biological justification.