Run zone 2 to build endurance

- Marathon Handbook explains Zone 2 running promotes mitochondrial biogenesis, increases fat oxidation, and is ideal for base aerobic development using an easy 'talk test' to set intensity. (marathonhandbook.com) - The guide recommends the talk test over obsessing about exact heart‑rate numbers for reliable, repeatable Zone 2 sessions in the field. (marathonhandbook.com) - Health Highroad bundles Zone 2 with sleep and other cortisol‑lowering habits as a low‑stress way to improve recovery and endurance. (healthhighroad.com)