Zone 2 training helps build your aerobic base, which is essential for endurance, recovery, and long-term cardiovascular fitness. Training in Zone 2 improves your ability to use oxygen efficiently, supports fat oxidation, enhances mitochondrial function, and allows you to accumulate more training volume without excessive fatigue. It is especially useful for runners, cyclists, hikers, mountain athletes, and anyone who wants to improve stamina without overtraining.

You should recalculate your zones every 4–8 weeks, or whenever your resting heart rate changes noticeably. As your fitness improves, your resting heart rate may decrease, which can slightly change your training zones. You should also update your zones after a long training break, illness, major weight change, or a new max heart rate test. For best accuracy, use a consistent resting heart rate measurement taken first thing in the morning.

The Karvonen Formula is a heart-rate training method that uses both your maximum heart rate and your resting heart rate to calculate more personalized cardio zones. Instead of only using a percentage of your max heart rate, it calculates your heart rate reserve, which is the difference between your max heart rate and resting heart rate. Formula:Target HR = ((Max HR − Resting HR) × Intensity) + Resting HR This makes the zones more individualized and useful for endurance training, fat loss, aerobic conditioning, and performance tracking.