Nolan & Moore 2021, Energy cost of run-walk pacing

Treadmill crossover (n=30 recreational runners). Frequent walk breaks slightly increased the energy cost of covering a given distance versus continuous running, about 4 kcal/km more (roughly 168 kcal over a marathon), because re-accelerating after each walk break is costly even though walking alone is cheaper per kilometre. The method is not a metabolic efficiency gain. Moderate (figures reported, full text paywalled).