A recovery score is not a mystery. It is a handful of overnight measurements compared with your own normal, then capped by sleep and training load. Improve the inputs and the score follows.
The inputs, and what raises each
HRV. The heaviest input. Sleep at a consistent time, less alcohol, easy aerobic exercise and slow breathing raise it. See the HRV guide for the detail.
Resting heart rate. The lowest sustained heart rate of the night. It falls with aerobic fitness over months and rises with illness, alcohol, dehydration, heat and hard training in the short term. A resting heart rate that is five beats above your normal is a louder signal than a small HRV dip.
Respiratory rate. Breaths per minute while asleep, from a watch worn to bed. It is very stable night to night, which makes a rise of a breath or two unusual, and often the earliest sign of illness.
Sleep. Sixteen caps recovery by last night’s sleep against your need. You cannot out recover a five hour night with good vitals. The sleep guide covers what to change.
Load. Recent training load sets another ceiling. Two hard days in a row will lower recovery even with perfect sleep, and that is the model working, not failing.
Journal. Alcohol, late meals, screens in bed, travel, illness. Logged, they explain the number. Over a few weeks the pattern tells you which one costs you the most.
What to do with a low day
A low score is information, not a verdict. Use it to change the dose: an easy session instead of intervals, an earlier night, a lighter evening. Sixteen does this for you by lowering the strain target and nudging the bedtime lock earlier. A low day handled well is usually followed by a green one.
What to do with a low week
A week of low scores with no obvious cause is worth taking seriously. The usual culprits, in order: an illness on its way, a run of poor sleep, accumulated training without easy days, alcohol on more nights than you thought, or a stretch of stress. Look at the journal, look at resting heart rate and respiratory rate together, and if both have shifted and stay shifted, see a doctor rather than a dashboard.
The compounding part
Recovery improves slowly and then all at once. Consistent sleep timing raises HRV a little. Higher HRV makes the hard days easier to absorb. Easier hard days mean more of them and better fitness. Fitness lowers resting heart rate, which raises recovery again. The loop takes weeks to show, which is why Sixteen scores trends and not mornings.
Sources
- Plews DJ et al. Training adaptation and heart rate variability in elite endurance athletes. Sports Medicine, 2013.
- Shaffer F, Ginsberg JP. An overview of heart rate variability metrics and norms. Frontiers in Public Health, 2017.
- Hirshkowitz M et al. National Sleep Foundation's sleep time duration recommendations. Sleep Health, 2015.
