Karvonen — heart-rate zones from your HR reserve
More accurate than %HRmax alone. Uses your real resting HR to personalize each zone. Run a 5-min rest measure in the morning before getting up — that's your true resting HR.
Tip: Karvonen reflects your fitness state. As your aerobic base grows, your resting HR drops and the zones shift down. Recalculate every 2-3 months.