Tired, or getting sick? Illness detection

The problem

A hard workout and an early infection produce almost the same overnight picture: both suppress HRV and nudge resting heart rate up. So HRV alone cannot tell "I trained hard" apart from "I am coming down with something" — and guessing wrong means either training into an illness or pulling you off a session you were fine for.

The signals training cannot fake

IntervalCoach leans on the overnight signals that a hard ride does not move: breathing rate, blood oxygen and skin temperature. When two or more of those drift off your personal baseline together, in the illness direction, it treats it as a likely oncoming illness rather than normal training fatigue.

What it does

On a day that pattern shows up, IntervalCoach eases the day toward recovery instead of sending you into the intervals your plan had queued, and your dashboard and Daily Briefing name the signals that triggered it — so it is a recommendation you can understand and overrule, not a black box. It also keeps that day out of what your recovery curve learns.

What you need

This needs a wearable that records breathing rate, blood oxygen and skin temperature overnight, such as a Whoop, Apple Watch or Oura. If all IntervalCoach has is HRV and resting heart rate, it deliberately stays quiet on illness rather than guess — a confident wrong answer is worse than none. See "Connecting your recovery data: Whoop and Apple Health".