A Review of High-Intensity Interval Training in Heart Transplant Recipients Current Knowledge and Future Perspectives

Objective: This review reports how exercise-based rehabilitation strategies have developed over the past decades, and it specifically focuses on the effectiveness, safety, and implementation of high-intensity interval training (HIIT). It provides an overview of the historical progression, main research findings, and considerations surrounding HIIT as the preferred exercise modality for recipients of heart transplant (HTx). Review Methods: The review includes a timeline of studies spanning from 1976-2023. The 2017 Cochrane systematic review on exercise-based cardiac rehabilitation in recipients of HTx serves as the main knowledge base (>= 2015). Additionally, literature searches in PubMed/Medline and ClinicalTrials.gov have been performed, and all reviews and studies reporting the effects of moderate- to high-intensity exercise in recipients of HTx, published in 2015 or later have been screened. Summary: High-intensity interval training has gained prominence as an effective exercise intervention for recipients of HTx, demonstrated by an accumulation of performed studies in the past decade, although implementation in clinical practice remains limited. Early restrictions on HIIT in HTx recipients lacked evidence-based support, and recent research challenges these previous restrictions. High-intensity interval training results in greater improvements and benefits compared with moderate-intensity continuous training in the majority of studies. While HIIT is now regarded as generally suitable on a group level, individual assessment is still advised. The impact of HIIT involves reinnervation and central and peripheral adaptations to exercise, with variations in recipent responses, especially between de novo and maintenance recipients, and also between younger and older recipients. Long-term effects and mechanisms behind the HIIT effect warrant further investigation, as well as a focus on optimized HIIT protocols and exercise benefits.