Fitness

Zone 2 cardio builds mitochondrial density that higher-intensity work cannot

Zone 2 training (below ventilatory threshold 1, conversational pace) specifically develops mitochondrial density and fat oxidation capacity. Research by Dr. Iñigo San-Millán at the University of Colorado demonstrates that elite endurance athletes spend 80% of training volume at Zone 2 intensity. The 80/20 polarized model (80% Zone 2, 20% high intensity) consistently outperforms threshold-heavy training in peer-reviewed studies.