Recovery metrics: HRV, sleep and resting heart rate

Many wearables reduce recovery to a single number: a "readiness" or "battery" score that promises to tell you, at a glance, whether you're ready today or not. The problem is that number hides several distinct physiological signals, often combined with proprietary weights that are never disclosed. This guide takes the opposite path: it separates out the metrics that make up the idea of "recovery", explains what each one measures, and shows you where you can calculate them yourself, with the explicit formula, for free.

The metrics, one by one

• •HRV (heart rate variability): how much the interval between one heartbeat and the next varies. Reflects autonomic nervous system activity, not average heart rate. Reference metric: RMSSD. Full guide + calculator →
• •Resting heart rate: the average beats per minute at rest, typically measured during sleep. A value that's stable over time for a given person, and tends to rise with acute physiological stress (illness, alcohol, overtraining).
• •Sleep duration: how many hours you actually slept, in total. An absolute number, not a ratio.
• •Sleep efficiency: what fraction of the time spent in bed was real sleep, not wakefulness. A ratio, not an absolute number. Full guide + calculator →
• •Sleep debt: the accumulation of missed sleep relative to your need, across multiple consecutive nights. A real concept discussed in the sleep literature, but FitMesh doesn't have a dedicated tool to calculate it today: we mention it here for completeness, not to promise a feature that doesn't exist yet.

How they connect (and why it isn't one number)

These metrics correlate but aren't interchangeable. You can sleep 8 hours (good duration) with low efficiency (a lot of time awake in bed). You can have HRV within your personal norm but an elevated resting heart rate for a night after drinking. A single score that combines them hides exactly these discrepancies, which are often the most useful information: knowing WHICH signal is off tells you more than a composite number that averages them together.

What these metrics are NOT

None of these metrics, alone or combined, is a diagnosis. They don't measure fitness, cardiovascular risk, or general health status. The literature they're based on (see the sources in the dedicated articles) describes them as most useful as a personal trend over time, under comparable conditions, not as an isolated value to judge from a single night.