Coach

From the Coach guide

Are your recent signals showing strain?

Recent heart rate, reflections, and training load help show strain.

The signals

Coach compares your recent overnight heart rate, your heart rate on easy runs and your HRV with your own baseline. It also uses how your runs felt and how similar your daily training loads have been.

What HRV is

HRV (heart rate variability) is how much the time between your heartbeats changes. It often goes down when you are tired. Apple Health records it in milliseconds, as SDNN. Some watches do not record it.

Where heart rate comes from

When available, the heart-rate comparison uses overnight readings located with Apple Health sleep data. The displayed bpm is the recent typical reading, not a recovery score.

Short sleep or stress

After a run, you can select Short sleep or stress. It counts like More tired than usual. If you report it often and your heart rate looks normal, Coach plans as if your fatigue is building. If your heart rate shows strain and you feel good, Coach goes by your heart rate. Coach chooses these responses to balance training with your recovery.

How to read it

One strain signal reads as Building; two or more read as High. Low means no strain was flagged in the available signals, not a guarantee of readiness.

Research and limits.

Small training study; app-defined interpretation

Overnight heart rate and recorded feelings

Nuuttila and colleagues studied 24 recreational runners through baseline, overload, and recovery periods. Changes in overnight heart rate and subjective recovery differed between runners with different training responses.

What this does not show

The study supports considering several signals together. It did not validate Coach’s feeling categories, fallbacks, percentage-of-baseline threshold, or Low/Building/High labels. Training-load variation adds context; it does not measure recovery directly.

Small study in trained triathletes; app-defined threshold

HRV as a weekly average

Plews and colleagues found that single HRV readings vary too much to read alone. A weekly average of at least 3 readings showed the change across a hard training period.

What this does not show

The study used a different HRV measure (Ln rMSSD) from the one Apple Health records (SDNN), and trained triathletes, not recreational runners. The 10% drop that counts as strain is an app choice, not a study value.

Continue reading.

How the overnight reading works

A consistent overnight window is compared with your own history.