Why did my workout get harder when I felt tired?

If IntervalCoach gave you a tougher session on a day you felt flat, it's because your *objective* recovery data looked good — even if your *subjective* feel didn't. Here's how that decision is made, and what to do if you disagree.

How the coach decides intensity

Every day, IntervalCoach reads your recovery signals — HRV and resting heart rate versus your personal 30-day baseline, sleep, and your TSB (form) — and adjusts the session up or down.

It only makes a day *harder* when your recovery is clearly good. A difficulty boost is allowed only when:

• Your recovery is green (roughly 67%+ on the recovery scale), and

• No fatigue signal has triggered a reduction, rest, or intensity cap.

If any signal calls for backing off — low recovery, accumulating fatigue, poor sleep, deep negative TSB — the boost is suppressed and the day gets easier or becomes rest instead. Very negative form (TSB well below zero) blocks an upgrade outright.

So a harder-than-expected session means the data said you were ready, even though you didn't feel it. That gap between feel and data is normal — and sometimes the data is right.

If you disagree with the call

You're always in control:

• Log how it went — add your RPE / feel feedback after a session. The coach learns which workouts feel harder for you and factors that in next time.

• Ask Coach+ — say "I'm tired today, give me something easier" or ask it to rebuild the day. It can adjust on the spot.

• Set a standing instruction — in Settings, add a custom instruction (e.g. "keep mid-week sessions endurance unless I'm well rested").

• Take the rest — mark the day as rest in your weekly schedule or Intervals.icu; the coach adapts the rest of the week around it.

Your health comes first — if you're genuinely run down, rest is never the wrong call.