Why Train in Zones?

Heart rate zone training ensures you work out at the right intensity for your goals. Running a faster 5K requires time in Zones 3 and 4; building endurance for a marathon or burning fat efficiently means spending most of your time in Zone 2.

The 80/20 Rule of Endurance Training

Elite endurance athletes spend about 80% of training time in Zone 2 (easy, aerobic) and only 20% in Zones 4–5 (hard, anaerobic). Amateurs often make the mistake of running every session in Zone 3 — too fast to recover, too slow to build high-end speed.

Finding Your True Max Heart Rate

Formulas provide estimates. Your true maximum heart rate is genetic and can only be definitively measured through a maximal stress test. The Karvonen method's advantage is that resting heart rate personalizes your zones to your current fitness.