In one sentence
How many beats per minute your heart rate falls in the first minute after you stop exercising, a direct reading of how quickly the nervous system's brake comes back on.
Why it matters
When exercise stops, the vagus nerve re-engages within seconds and the heart slows; how fast it slows is a measure of that brake's strength, the same system overnight HRV reads from the other side. It is one of the oldest exercise-test numbers with outcome data behind it. In 2,428 adults referred for a treadmill test and followed for six years, a fall of 12 beats or fewer in the first minute of a walking cool-down was the cut-point Cole and colleagues chose, and the people below it had about twice the all-cause mortality of those above it after adjustment (Cole 1999). For a healthy person the useful reading is the trend: recovery speeds up with aerobic fitness and slows when you are run down.
What moves it
Upward over months: aerobic training. Downward on a day: fatigue, a hard session the day before, heat, dehydration, being unwell, caffeine late, a session that ended at a lower effort than usual (there is less to recover from). The protocol matters more than for any other number here: Cole's cut-point was for a walking cool-down after a maximal test, and a watch that reads your recovery after an easy ride, while you sit down, is measuring a different thing. Compare only like with like.
How to measure it well
Let the watch take it the same way every time: stop, stay upright and still or walk slowly, and do not start the next thing for a minute. If you record it by hand, note your heart rate at the last hard minute and exactly one minute after stopping.
How Vitality Tracker uses it
Stored as one figure per day, from the device or typed in, and charted over time. It feeds no engine yet; Capacity reads the overnight readings instead. It is here so that the series exists when you want it.
How far to trust the number
Measured: a heart rate at two moments. What varies is the protocol, so the series is only comparable with itself under the same routine.
Sources
- Cole CR, Blackstone EH, Pashkow FJ, Snader CE, Lauer MS. Heart-rate recovery immediately after exercise as a predictor of mortality. N Engl J Med 1999;341:1351–7. doi:10.1056/NEJM199910283411804.