Most apps treat heart rate variability (HRV) as a single recovery score — a number that's "good" or "bad" today. Chronobiology offers a richer view: HRV reflects how harmoniously your body's many rhythms work together. As the Austrian-German chronobiologist Maximilian Moser puts it, every organ system produces its own "sound" — from the fast rhythms of the nervous system, through the heartbeat and breath, down to the slow tempo of metabolism — spanning seconds to weeks. HRV is a window into whether these rhythms are playing in tune or out of sync. Seen this way, a high HRV isn't just "good recovery"; it's a sign your internal orchestra is well conducted.
Beyond the recovery score
The Anglo-American wearable world flattened HRV into a morning readiness number. Useful, but it hides what HRV actually measures. Your heartbeat naturally speeds up as you inhale and slows as you exhale — a rhythm called respiratory sinus arrhythmia. That coupling between breath and heart is one small example of the body's rhythms coordinating. HRV quantifies the flexibility and coordination of these autonomic rhythms.
When your body is well-regulated, its rhythms nest and synchronize: breath modulates heartbeat, heartbeat aligns with blood-pressure waves, and daily circadian cycles set the backdrop. When you're stressed, sick, or living against your clock, this coordination breaks down — and HRV drops. So a falling HRV isn't just "you're tired"; it's "your rhythms are losing their harmony." (This is also why there's no single "good" number — see normal HRV by age.)
The rhythms that make up the harmony
Chronobiology describes the body as a nested set of oscillations, each with its own timescale:
- •Fastest — the nervous system, firing in fractions of a second.
- •Heartbeat and breath — cycling in seconds, and directly coupled (the basis of HRV).
- •Blood pressure waves — slower oscillations that synchronize with breathing at around six breaths per minute.
- •Circadian rhythm — the 24-hour cycle governing sleep, temperature, hormones and heart rate.
- •Slowest — metabolic and hormonal cycles, unfolding over days to weeks.
Health, in this view, isn't any single rhythm being "right" — it's how well they interact and adapt together. HRV is one of the few non-invasive windows into that interaction.
Why coherence feels calming
This reframing explains why slow, paced breathing works so reliably. Breathe at about five to six breaths per minute and something striking happens: your heart-rate rhythm and your blood-pressure rhythm fall into resonance, oscillating together at roughly 0.1 Hz. Physiology describes this as the point where the cardiorespiratory system swings in maximum resonance, optimizing the baroreflex and raising vagal modulation. Subjectively, it feels like calm. Physiologically, it's your rhythms synchronizing — harmony you can create on purpose, in a few minutes, with your breath. That resonant pace is personal; you can find your own resonance rate and train it with coherent breathing.
This is why "coherence" is a better word than "relaxation" for what breathing practice does. You're not just calming down; you're bringing your body's oscillators into phase.
What throws the rhythms out of tune
The same things that lower HRV are, in this framework, sources of rhythmic disorder:
- •Social jet lag — living against your circadian clock desynchronizes the daily backdrop all other rhythms hang on.
- •Chronic stress — locks the nervous system in "on," flattening the natural ebb and flow.
- •Shallow, fast breathing — decouples breath from heart, suppressing respiratory sinus arrhythmia.
- •Alcohol and poor sleep — disrupt the overnight window where rhythms normally resynchronize.
See your own harmony
Because HRV reflects coordination, not a single value, it's most meaningful as your own pattern over time. ONDA reads your resting heart rate, HRV and breathing and shows your personal baseline — and, during a practice, lets you watch your pulse fall into rhythm with your breath in real time. Instead of a lone morning score, you see your rhythms actually synchronizing, which is what raising HRV really means.