Learn → HRV
What is HRV?
Heart rate variability is the variation in time between consecutive heartbeats. A healthy heart is not a metronome — and that irregularity is the point.
If your heart rate is 60 beats per minute, the beats are not landing exactly one second apart. One gap might be 1.05 seconds, the next 0.94. HRV measures that variation, usually in milliseconds.
Why the variation matters
Two branches of your autonomic nervous system are constantly negotiating: the sympathetic branch (the accelerator — stress, effort, alertness) and the parasympathetic branch (the brake — rest, digestion, recovery). The push and pull between them is what makes the spacing between beats vary.
When you are well recovered, the brake has more influence and the spacing varies more. When you are stressed, ill, under-slept or still recovering from hard training, the accelerator dominates and the spacing becomes more uniform. So HRV is really a window onto which branch is currently winning.
What high and low HRV mean
Higher than your normal
Generally reflects good recovery, lower stress load, and a nervous system with capacity to spare.
Lower than your normal
Can reflect fatigue, psychological stress, poor or short sleep, alcohol, hard training not yet recovered from, or the early stages of illness — often a day or two before you feel it.
The mistake nearly everyone makes
Comparing your HRV to someone else's is close to meaningless. Healthy adults range from roughly the teens to well over 100 ms, and where you sit is driven heavily by age and genetics. A 25 ms reading can be perfectly normal for one person and a warning sign for another.
What carries information is your number against your own recent baseline. That is the only comparison Biomon makes: your 7-day average against your own 30-day baseline, using the smallest-worthwhile-change method from sports science. It never scores you against a population.
What influences HRV
- Sleep — both duration and quality. Usually the single largest lever.
- Psychological stress — deadlines and conflict show up here as clearly as physical strain.
- Training load — hard sessions suppress HRV for a day or more; that is normal and expected. Persistent suppression is the signal worth noticing.
- Alcohol — one of the most reliable and dramatic single-night suppressors.
- Illness — often drops before symptoms appear.
- Hydration and timing of meals — smaller, but real.
- Age and genetics — set the range you operate in. Not something to fight, just to know.
One detail most apps don't tell you
Sports-science literature usually means rMSSD when it says HRV. Apple Watch does not expose rMSSD for overnight background readings — it exposes SDNN, a related but different measure over a longer window. Biomon uses SDNN natively rather than converting it and pretending otherwise, and says so.
That matters practically: your Apple Watch HRV will not match a chest-strap rMSSD figure, and neither is wrong. It is another reason to track your own trend rather than chase a number you read somewhere.
How to actually use it
Do not react to one reading. A single low night could be a late meal, a glass of wine, or a poorly-worn watch. What is worth acting on is a direction — several days below your baseline, especially alongside a raised resting heart rate, which together suggest you are genuinely under-recovered rather than just having an odd night.
That combination is exactly what Biomon watches for, and it will tell you which of the two it is seeing rather than blending them into one score.
Related
Sleep debt →
The single biggest thing moving your HRV.
Body battery →
What your HRV gets turned into, and who actually invented it.
VO2 Max →
The fitness measure you can actually change.
This is general wellness information, not medical advice. Biomon is not a medical device and nothing here is a diagnosis. If something about your health concerns you, talk to a doctor.