This is a physiological estimate. Consult a professional for clinical stress testing.
Why Zone 2?
Zone 2 is an aerobic intensity where you can speak in full sentences, build mitochondrial fitness, and improve fat oxidation — without accumulating
excessive fatigue.
Heart rate zones depend on individual physiology. The Karvonen (heart rate reserve) method weights your resting rate so the range reflects your
cardiovascular economy more closely than age-only formulas.
The HUNT option estimates max HR from the HUNT study equation (211 − 0.64 × age, rounded) when you do not have a reliable measured max.