CoachFrom the Coach guide
Your runs choose your zones.
How Coach chooses between threshold zones and heart-rate reserve zones.
Two ways to set zones
Heart-rate reserve zones come from your maximum and resting heart rate. Threshold zones come from the heart rate of your last threshold test.
What Coach checks
For each run with heart rate and a rating, Coach finds its zone both ways. Then it checks which zone agrees with how hard you said the run felt. Coach also counts your easy runs in zones 1–2 both ways.
When Coach changes your zones
Coach changes your zones only when one way agrees clearly more often. It uses a standard statistics test, at 95%. At least 6 runs must agree with one way and not the other. Coach tells you once, and you can undo the change.
Limits
Coach uses only runs after a threshold test with heart rate. A rating is less exact than a zone, so each rating matches two zones. If you choose your zones in Settings, or set your own zone limits, Coach keeps your choice.
Where this comes from
Threshold zones follow Friel's running zones. Heart-rate reserve zones follow Karvonen. How Coach matches a rating to zones is an app choice.