Understanding how we should - and should not - use HRV as a biomarker for rest & recovery.
If you zoom into a healthy heartbeat, you’ll notice something surprising. It’s not steady.
Each interval between beats changes slightly — speeding up and slowing down from one to the next. This pattern is called heart rate variability, or HRV.
The word variability can sound like imperfection. But here, variation is a sign of health. HRV reflects the constant negotiation between your body’s two control systems:
Every heartbeat is a reflection of that conversation. HRV isn’t just a number, but a mirror of how gracefully your nervous system adapts to change.
At its core, HRV is a measure of time: the variation in milliseconds between consecutive heartbeats, known as inter-beat intervals (IBIs).
A metronomic heart — perfectly even beats — would actually be unhealthy. It means the autonomic nervous system (ANS) has stopped fine-tuning the rhythm. In contrast, a heart that fluctuates rhythmically shows adaptability, readiness, and physiological resilience.
You can think of HRV as a window into autonomic flexibility — how fluidly your body can shift between activation and recovery.
A flexible heart is a responsive heart.
When HRV is high, the body can react quickly to changes: stand up, breathe deeper, face a stressor, then settle back down.
When HRV is low, the system becomes rigid — locked in either acceleration or braking, like a car stuck in one gear.
This is why HRV correlates with so many health domains: cardiovascular endurance, stress resilience, sleep quality, emotional regulation, even immune response. It’s not the cause of these things; it’s the mirror.
But context matters. HRV naturally decreases during exertion, illness, or sleep deprivation. It also varies with age, genetics, and time of day.
The key isn’t whether HRV is “high” or “low,” but whether it behaves appropriately — rising during rest, recovering quickly after stress, and showing rhythmic modulation during slow breathing.
There are dozens of HRV metrics, each capturing a slightly different angle of the same underlying rhythm. The most common are:
Each of these can be informative — but only in context. HRV is not a single number that lives in isolation.
During slow, controlled breathing, for instance, HF power (normally considered vagal) collapses simply because the breathing frequency moves below the HF range. LF power, meanwhile, surges — but it’s still entirely parasympathetic. Unless you understand that context, you’d misread the data.
That’s why HRV can be confusing: it’s dynamic, contextual, and frequency-dependent.
Breathing is the dominant driver of short-term HRV. Each inhale speeds the heart slightly; each exhale slows it down. This oscillation — respiratory sinus arrhythmia (RSA) — is one of the clearest signatures of parasympathetic activity.
When you breathe around 0.1 Hz (about six breaths per minute), this oscillation enters resonance — a state where the rhythms of the heart, lungs, and baroreflex align perfectly.
In this state, HRV amplitude becomes large, smooth, and rhythmic. The signal isn’t just variable — it’s coherent.
This is the physiological foundation of resonance breathing, and why techniques that train HRV through breathing are so effective. They don’t just increase variability; they improve coordination across multiple systems.
Modern wearables often compress this complexity into a single score. It’s convenient, but it hides nuance.
A high HRV score could come from irregular, noisy variability (e.g., caffeine, movement) rather than coherent parasympathetic modulation.
A lower HRV score could appear during slow, even breathing — a pattern that’s physiologically excellent.
And because most devices take brief, intermittent samples (often while you sleep), they miss the continuous dance that happens throughout the day.
HRV isn’t just magnitude; it’s shape, timing, and context.
That’s why Ohm takes a different approach. Rather than collapsing everything into one number, it looks at three interrelated dimensions — heart rate, amplitude, and resonance — to capture the system’s load, capacity, and efficiency in real time. (See The Ohm Triad of Metrics.)
Consistency reveals adaptation. The goal is not to reach a number, but to see the curve shift: steadier waves, faster recovery, stronger oscillations.
Most wearables record HRV passively, like a thermometer reading temperature.
Ohm works like a thermostat — continuously sensing and adjusting.
By guiding your breathing into resonance and measuring HRV in real time, Ohm turns variability into feedback. It helps the body learn its own natural tempo of calm.
Instead of analyzing data after the fact, you experience the shift as it happens — light, sound, and vibration reflecting your internal rhythm.
In that sense, HRV isn’t the outcome. It’s the language.
And the practice isn’t about chasing numbers, but about training responsiveness — teaching your body how to find balance again and again.
A healthy heart is not a metronome.
Its rhythm stretches and contracts with every breath, thought, and emotion. HRV is that elasticity made visible — a measure of how fluidly we move between effort and ease.
We can’t control every beat, but we can shape the patterns that emerge between them.
That’s the real gift of HRV: it shows that adaptability itself can be cultivated.
Each slow, steady breath is a small act of training — a conversation between heart and brain that gently nudges the autonomic nervous system back into balance.
Laborde, S., Mosley, E., & Thayer, J.F. (2017). Heart rate variability and cardiac vagal tone in psychophysiological research.Frontiers in Psychology.
