Wearables: what your watch measures well (and what it only estimates)
I rely on good instruments, and wearables democratized an arsenal of data that once existed only in a lab. But confusing an estimate with absolute truth is a tactical error. Let's separate what your watch truly knows from what it merely deduces.
What they measure well
- Heart rate: at rest and in moderate activity, modern wrist sensors are quite reliable.
- Steps and movement: good accuracy for daily activity trends.
- Heart rate variability (HRV) and resting rate: useful as thermometers of recovery and stress, mainly tracking your own trend over time.
- Heart rhythm alerts: some devices detect patterns like atrial fibrillation and have already prompted many people to see a doctor.
What they only estimate (with a margin of error)
- Calories burned: notoriously imprecise. Treat it as a rough estimate, not truth to base a diet on.
- Sleep stages: the watch reasonably nails total sleep time, but the split into light/deep/REM is an estimate that can be quite off.
- VO₂max and 'fitness age': useful estimates for tracking progress, not lab numbers.
- Oxygen saturation and other metrics: vary in quality by device and conditions of use.
How to use it without becoming a hostage
- Focus on the trend, not the isolated number: today's value matters less than the direction over weeks.
- Use it as a signal, not a sentence: a bad data point is an invitation to investigate (slept poorly? overtrained?), not a reason to panic.
- Beware data anxiety: chasing the perfect sleep score can worsen your sleep (orthosomnia). The gadget serves you, not the reverse.
- Don't self-diagnose: the watch's health alerts are to take to a doctor, not to conclude on your own.
A word from the Lair: this content is informational and does not replace medical care. Wearable health alerts should be confirmed by a professional; they don't replace tests.
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