Moderate–intensity double interval training to prepare the bike-to-run transition in long-distance triathletes: A narrative review

There is currently no well-defined progression from single-modality training to combined-modality sessions in long-distance triathlon. This review aims to present a theoretical and practical framework for implementing moderate–intensity double interval training (DIT) —structured for the bike-to-run transition (i.e., morning cycling session followed by an afternoon running session)—, as an intermediate step in the progression from single-modality to combined-modality or brick workout sessions in long-distance triathletes. A literature search was conducted in PubMed, Scopus, Web of Science, and SPORTDiscus, with additional sources identified through Google Scholar, covering publications from database inception to 10 January 2026. Evidence relevant to endurance exercise physiology, interval training methodology, durability during prolonged exercise, and triathlon performance—particularly the bike-to-run transition—was selectively integrated, drawing on a broad body of literature covering 75 publications, including experimental studies in endurance athletes, physiological investigations in humans, and applied or conceptual literature on endurance training and triathlon performance. The review was prepared in accordance with the SANRA guideline for narrative review quality assessment. Based on this integrated body of evidence, moderate–intensity DIT with long, prolonged intervals could serve as a practical and theoretically grounded methodological strategy to replicate and prepare for specific demands of the bike-to-run transition in long-distance triathletes. Because running performance often deteriorates in this phase, training under these simulated conditions might help limit this decline. Nevertheless, further empirical and field-based validation is needed to support its integration into training prescription and periodization.