Resonance: the app to train your nervous system

Why I built Resonance

During the first weeks of my mental performance training, I was asked to do one simple thing: practice heart coherence every day, for 8 weeks.

I did what everyone does. I downloaded an app with a bubble that goes up and down.

It works. The rhythm settles in, the body comes down, and after a few weeks the effects are there. I wrote about it in an article.

But something was missing.

A bubble going up and down is a timer. It does not tell you whether your heart is following. It does not tell you whether you are progressing. It does not tell you what to do at 2pm, two minutes before a meeting that matters, when you do not have 5 minutes to spare.

And above all, it trains only one side: coming down.

In sport, you do not only train to recover. You train to take it. In an Ironman, the pain comes. You do not remove it. You learn to stay composed inside it.

That is exactly what I wanted for the moments that tighten in a founder's life: the pitch, the board, the hard announcement to the team, the night before a raise.

Resonance was born from that. An app that trains the nervous system like a muscle, in both directions, and measures it.

What Resonance is not

Better to say it up front, because the market is full of breathing apps.

• It is not a wellness app. It is built for action, not for the couch. The ambient soundscape exists, it is optional, and so is silence.
• It is not a timer with a bubble. The visual guide exists, but it serves a path and a set of metrics.
• It is not a medical device. It diagnoses nothing, treats nothing, and does not replace professional advice.
• It is not one more account. No account, no server, no data collected. Everything stays on your phone.

What it is: a training. With sessions, steps, numbers, and the same logic as a race plan.

The principle: two sides

The stress response is not something you decide. It is something you train.

When pressure rises, your nervous system tips into sympathetic mode: heart speeds up, breath gets short, attention narrows. You do not choose that reflex. But you can train two things: how fast you come back down, and the threshold at which you tip over.

Resonance works on both.

Side 1: descent

Bringing the pressure down. This is the vagal brake: slow down, release, let the nervous system return to calm.

• Resonance breathing (heart coherence, at your own frequency)
• Long exhale and physiological sigh
• Box breathing and body scan

Side 2: confrontation

Widening your tolerance. Staying composed when it tightens, taming discomfort instead of running from it.

• Personalized CO₂ tables
• Breath-holds and dry apnea
• Contrast: raise the pressure, then come back down

The path alternates the two. One session to come down, one session to take it, and little by little what you can go through gets wider.

That is the difference between a relaxation practice and a training. Relaxation brings you back to calm. Training moves your threshold.

What is in the app

The programs

Guided paths, step after step, that adjust to how you are today:

• 7-day discovery: the basics, heart coherence and first breath-holds
• Mastering calm: the descent side, in depth
• Sleep better: long exhale and sleep-onset protocols
• Meditate: body scan and mindfulness
• Advanced apnea: 56 sessions for those who want to go far on CO₂ tolerance

Before each session, a note explains why it matters. No guilt-tripping calendar: you move at your own pace, and the path adjusts if you missed a week.

The toolkit

For the precise moment, when you do not have twenty minutes. One tap, and you are in:

• Physiological sigh · 90 seconds: the fastest documented reset
• Activation · 2 minutes: before an effort, a pitch, a talk
• Box breathing · 4 minutes: to steady and focus
• Heart coherence · 5 minutes: the foundation, at your frequency
• Long exhale: to come down, fall asleep, fall back asleep at 3am
• CO₂ table · 12 minutes: to take it

The meditations

Body scan and mindfulness, from 5 to 20 minutes. A natural studio voice, female or male, your choice. Offline.

Free sessions

You pick your rhythm and your duration, outside any program. Useful when you know exactly what you want.

The three metrics

This is what mattered most to me. Measurements, not impressions.

BOLT: your CO₂ tolerance

The BOLT (Body Oxygen Level Test) measures how many seconds you hold, after a normal exhale, before the first urge to breathe. Not to the limit: to the first signal.

This score reflects how sensitive your system is to CO₂. A nervous system on permanent alert has a low BOLT: it triggers the urge to breathe very early. When your stress response calms down, the BOLT goes up.

Orders of magnitude:

• Under 15 seconds: chronically short breathing, system on alert
• 20 to 25 seconds: average for active adults
• Above 30 seconds: solid tolerance
• 40 seconds: level of well-trained endurance athletes

What counts is your trend, measured in the morning, under the same conditions.

Resonance: your frequency, measured

Heart coherence is practiced at 6 breaths per minute by default. But the frequency at which your heart and your breath align best is personal. Depending on the person, it sits between 4.5 and 7 breaths per minute.

With a chest strap, Resonance tests several rhythms and finds yours on your own curve. You then practice at your frequency, not at the average protocol's. The difference in effect on heart rate variability is real.

Recovery: the time to come back down

How many seconds between pressure and calm. After a breath-hold or a CO₂ table, the app measures how long your heart takes to return to its resting level.

This may be the most telling metric for a founder. The question is not "am I stressed". It is "how long do I take to come down after a spike". And above all: how it shortens, week after week.

Heart biofeedback

Connect a Bluetooth chest strap (Polar, Garmin, Wahoo or equivalent) and you watch your heart align with your breath, live.

On screen: your heart rate curve, the guided breath, and a coherence score that tells you whether your breathing is producing the expected effect.

Why a strap and not the watch? Because the strap measures every single beat. Watches and rings are very good for the overnight trend, I cover that in the HRV guide. They are much less precise for seeing what happens live over 5 minutes.

The strap is not required. Everything else works without it. But if you want to see rather than believe, this is where it happens.

How to use it in a founder's day

About 10 minutes a day. Here is how I structure it.

• On waking: BOLT measurement (30 seconds), then 5 minutes of heart coherence at your frequency. You start with a regulated nervous system and a number.
• Before a high-stakes meeting: physiological sigh, 90 seconds. In the elevator, in the hallway. Nobody sees it.
• After a hard call: express reset. So you do not carry it into the next one.
• Before a talk or an effort: activation, 2 minutes. Here you are not looking for calm, you are looking for availability.
• In the evening: long exhale. The transition between the office and home.
• 3am: long exhale, sleep version. Without turning on the light.
• 3 times a week: one session of your current program. That is where the threshold moves.

What you trained cold is available hot. That is the whole principle. The protocol you trigger 90 seconds before the pitch, you have rehearsed fifty times when nothing was at stake.

Common mistakes

Chasing a score instead of a practice

The BOLT is an indicator, not a goal. Forcing it by holding to the limit distorts the measurement and does not train you.

Only doing the descent

It is comfortable. But if you never work the confrontation side, your threshold does not move. You come down well, and you still tip over just as early.

Practicing breath-holds in water or while driving

Never. Training is done dry, seated or lying down. A breath-hold can cause a blackout. In water, it kills.

Comparing your BOLT with other people's

As with HRV, the absolute value depends on your age, your fitness, your genetics. Your trend is the only useful number.

Waiting for the strap to start

Biofeedback is a plus. Practice is the essential. A founder doing 5 minutes a day without a strap progresses more than one waiting for the right gear.

Doing everything at once

An app with twenty or so protocols is tempting. Start with the 7-day program. Add the toolkit once the foundation is in place.

Resonance vs other apps

These tools are not all competitors. A ring for the overnight trend and Resonance for daytime training complement each other very well.

What sets Resonance apart comes down to two words: training and measurement. Both sides, and numbers that move.

What the research says

Resonance does not rest on a science of its own. It assembles documented protocols, with different levels of evidence that I prefer to present as they are.

• Resonance frequency breathing: the work of Paul Lehrer and Richard Gevirtz has shown since the 2000s that breathing at your resonance frequency, around 6 per minute, maximizes heart rate variability amplitude and the baroreflex. This frequency varies from one person to the next, hence the value of measuring it rather than taking the average.
• Heart rate variability biofeedback: the meta-analysis by Goessl et al. (2017, Psychological Medicine), across 24 studies, finds a large effect of HRV biofeedback on stress and anxiety.
• Physiological sigh: the study by Balban et al. (2023, Cell Reports Medicine, from Andrew Huberman's and David Spiegel's labs at Stanford) compares 5 minutes a day of cyclic sighing, box breathing, controlled hyperventilation and meditation. Cyclic sighing produces the largest improvement in mood and the largest drop in resting respiratory rate.
• CO₂ tolerance and BOLT: the BOLT comes from the Buteyko method, popularized by Patrick McKeown. It is a field indicator, practical for tracking a trend, but far less documented in the literature than HRV. I present it as such.
• Box breathing: used by military units for decades to steady themselves under stress. Studies are fewer but converge on a short-term regulation effect.
• Breath-holds and exposure to discomfort: work on apnea and on interoceptive exposure suggests that learning to stay calm in front of the "I need to breathe" signal increases tolerance to physiological discomfort. An emerging field.

Honest summary: the descent side is very well documented. The confrontation side less so, but its principle (expose, then recover) is the principle of every sports training.

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