Zones

Five zones, your threshold

Age-formula zones are a guess. Pulse tunes your five zones to your actual heart-rate threshold, so "zone 2" actually means zone 2.

The zones

z1  recovery       < 60% of max
z2  base           endurance building
z3  tempo          threshold-adjacent
z4  threshold      your 1-hour limit
z5  anaerobic      short and sharp

Why it matters

Most people run their easy days too hard and their hard days too easy. Real zones fix both.