Zone 1 · Warm-upvery light effort—
Zone 2 · Fat burnlight, sustainable for a long time—
Zone 3 · Cardiomoderate, builds endurance—
Zone 4 · Thresholdhard, near the limit—
Zone 5 · Maxmaximal, short bursts only—
220 − age is a rough estimate. For precise zones, a max-HR lab test is more reliable.