The parasympathetic nervous system: your body's brake and how to use it

The parasympathetic nervous system has become a popular topic over the past few years, often wrapped in promises that make me wince. Yet the basic idea is simple and useful: your body has a brake. A mechanism that slows your heart, restarts your digestion and helps you recover after a tense stretch.

I am a sophrologist, hypnotherapist and wellbeing coach in Bordeaux. Before that, I spent years working in start-ups, with my foot on the accelerator from morning to night, until I burnt out. I had never heard the word "parasympathetic". All I knew was that I could no longer come down, not even on holiday, not even on a Sunday.

Here you will find what this system does, without jargon, how to tell when your body is stuck in alert mode, and four exercises I teach in sessions to help it slow down.

The parasympathetic nervous system, in plain words

Much of what goes on in your body runs without you. Your heart speeds up when you climb the stairs, your digestion starts after a meal, your temperature adjusts itself. That is the work of the autonomic nervous system, "autonomic" because it works without you having to think about it.

According to the MSD Manual, a medical reference written for the general public, this system regulates blood pressure, heart rate, breathing, digestion, body temperature and the production of saliva, sweat and tears, among other things. It has two main branches: the sympathetic and the parasympathetic nervous systems.

The parasympathetic branch is the one that conserves and restores. It runs the body in ordinary situations. It slows the heart rate, lowers blood pressure and gets the digestive tract to digest food and clear waste. The energy from your meals then goes into repairing and rebuilding tissue. It is sometimes called the "rest and digest" system, and the nickname sums it up well.

The vagus nerve, its main messenger

Most of this work goes through a nerve that runs from the brainstem down to the abdomen, passing the heart and lungs on the way: the vagus nerve. A review from the University of Bern describes it as the main component of the parasympathetic nervous system. One detail surprised me the first time I read it: 80 to 90% of its fibres carry information from the organs up to the brain, and only 10 to 20% carry signals from the brain down to the organs.

In other words, your brain listens closely to what your body tells it. That is one reason why you can change how you feel inside by working with your breath. I will come back to the vagus nerve in more detail in a separate article.

Sympathetic and parasympathetic: the accelerator and the brake

The picture I use most often in sessions is a car. The sympathetic system is the accelerator. The parasympathetic system is the brake. You need both, and a car with only one of them would be dangerous.

The sympathetic system gets the body ready to face danger, to fight or to run. The MSD Manual lists what it sets off: the heart beats faster and harder, the airways open, stored energy is released and muscles get stronger. Palms sweat and pupils widen. Anything that is not urgent, such as digestion, is put on hold.

The parasympathetic system does roughly the opposite on the same organs. It slows the heart, lowers blood pressure and restarts digestion. The two systems do not take turns like a light switch: they work at the same time, all the time, and the balance between them shifts with what you are going through.

How to tell the difference in your body

You do not need a gadget to know which way the balance is tipping. A few pointers are often enough.

Leaning towards the accelerator:

• you can feel your heart beating, even sitting down;
• your breathing is short and high in your chest;
• clammy hands, a dry mouth;
• a knotted stomach, no appetite, or a digestion that drags;
• a clenched jaw, shoulders up by your ears.

Leaning towards the brake:

• your breathing drops towards your belly;
• you no longer notice your heartbeat;
• saliva comes back, your stomach rumbles a little;
• you feel like yawning, with a pleasant heaviness in your arms.

None of these signs is serious in itself. They simply show which mode your body is in at that moment.

When the body stays stuck on alert

The accelerator is not the problem. It is what lets you speak in front of a group, dodge a bike coming at you, or finish a project on time. What wears you out is when your foot never comes off the pedal.

That was me, towards the end of my start-up years. I went to bed exhausted and woke up with my heart already racing, the day's to-do list in my head before I had opened my eyes. I ate fast, standing up, without being hungry. I put it down to the pace of the job. Looking back, my body simply never got a chance to brake.

What I often see in the people I work with looks much the same. They come in saying they "can't switch off". They sleep badly, digest badly, jump at the slightest thing, and the weekend is no longer enough to recover. It is not a lack of willpower. The body has got used to staying on alert.

What is not my job

Some signs call for an appointment with your doctor first, not a breathing exercise: palpitations, dizzy spells or feeling faint when you stand up, digestion that has been difficult for weeks, tiredness that rest does not shift. Sophrology does not replace medical advice. It can support you once your doctor has checked that everything is fine, or alongside whatever they suggest.

Why breathing is the way in

You cannot decide to slow your heart down. You cannot tell your stomach to digest. But you can decide to breathe more slowly, and breathing is closely linked to the autonomic nervous system. It is the handle the body leaves within our reach.

This is not just a sophrologist's hunch. A meta-analysis of 223 studies led by a team at the German Sport University Cologne found that voluntary slow breathing increases the heart rate variability linked to the vagus nerve. The effect shows up during the exercise, right after a session, and after a training programme of several sessions too. This variability is one of the most widely used ways of measuring parasympathetic activity on the heart.

Another review of fifteen studies, carried out at the University of Pisa in healthy people, points the same way. Breathing at fewer than ten breaths a minute goes with higher heart rate variability, and participants report feeling more relaxed, comfortable and energetic, with less agitation and anger.

Why the out-breath matters so much

When you breathe in, your heart speeds up slightly. When you breathe out, it slows down a little. This small back-and-forth is normal, and it is exactly what heart rate variability means. By lengthening your out-breath, you give more room to the phase where the brake is working. That is why, in almost every exercise I suggest, the out-breath lasts longer than the in-breath.

Four exercises to activate the parasympathetic nervous system

These are exercises I teach in sessions, which people then practise on their own. You can do them sitting, standing or lying down, with no equipment. Pick one or two, not all four: what counts is doing them regularly, not doing a lot.

1. The long out-breath

Sit with your back straight but not stiff. Breathe in through your nose for a count of four. Breathe out slowly, through your mouth or nose, for a count of six. If that feels easy, go up to eight. Keep going for two to three minutes.

Never force it. If you feel short of breath or light-headed, go back to a more comfortable pace. The aim is to slow down, not to break a record. If you like this exercise, heart coherence breathing is a more structured version, with a steady rhythm and a set length of time.

2. Breathing into your belly

Place one hand on your chest and the other on your belly, just below your navel. Breathe normally and notice which hand moves more. For many stressed people, it is the top one.

Then, as you breathe in, let your belly swell gently under your hand, like a balloon. As you breathe out, let it fall back without pulling it in. The hand on your chest barely moves. Take about ten breaths like this. I often have people do this lying down at first, because the belly relaxes more easily.

3. Tense to let go

This is a dynamic relaxation movement, widely used in sophrology. Standing up, breathe in as you clench your fists and lift your shoulders towards your ears. Hold your breath for two or three seconds, keeping the tension. Then let everything go at once, breathing out slowly through your mouth, and let your arms drop.

Stay still for a few seconds afterwards, eyes closed if you like, and notice what is happening in your shoulders, hands and neck. That pause after the release is the most important part. Do the movement three times.

4. The bedtime release

In bed, before you go to sleep, scan your body from top to bottom. Your forehead, eyes and jaw: let them soften, with your tongue resting at the bottom of your mouth. Then your neck, shoulders and arms down to your fingertips. Your belly, back, legs and feet. With each area, a slightly longer out-breath.

You may discover tension you have been carrying since the morning without knowing it. It does not matter if you fall asleep before the end; if anything, that is a good sign.

When to fit them into your day

The best time is before the tension climbs too high. I often suggest three fixed slots: in the morning before you open your emails, after lunch, and at bedtime. Two minutes is enough. Add one more whenever you notice your first warning sign, whether it is your jaw, your shoulders or your heart. If you find that sign hard to spot, I go into it in detail in my article on managing stress and emotions.

What I take from the science, and what I leave out

The parasympathetic nervous system has become a selling point. You will find promises about longevity, inflammation and protection against all sorts of health problems. Some of these leads are being studied seriously by medical researchers, often with electrical stimulation devices used by doctors. But none of that means a breathing exercise protects you from anything.

What I take from it, and it is plenty for me: slow breathing helps the body put the brake on, it can be measured on the heart, and people who practise it say they feel more relaxed. The Bern review also notes that vagal tone is linked to the ability to regulate stress and that it can be influenced by breathing. That is already a lot.

I stay cautious about the rest. I will not tell you that an exercise will fix a digestive problem, months of poor sleep or high blood pressure. Those are questions for your doctor. What I can teach you is how to give your body regular chances to recover, and how to notice sooner when it needs one.

Watches and apps

Many watches now display a heart rate variability reading or a "stress score". If that motivates you, why not. But I also see people getting stressed about their score, which rather misses the point. Your own sensations remain the best guide: your breathing, your shoulders, the way you sleep.

Going further with sophrology

Sophrology works on exactly this ground: breathing, muscle relaxation and paying attention to physical sensations. It is not one more technique to squeeze into an already full day. It is a way of teaching your body that it is allowed to brake, and then letting it do so more and more naturally.

In sessions, we start from your real pace of life. Together we identify your warning signs, choose the exercises that suit you and adapt them to your constraints. If you recognise yourself in the description of a body that never switches off, with exhaustion setting in, talk to your doctor.

I see people at my practice as a sophrologist in Bordeaux, on rue Ducau. I also offer online sophrology if you live further away or are short of time. My background and training are on the about page.

In the meantime, try the long out-breath tonight, for two minutes, and notice how you feel. And if you would like support to turn it into a habit, you can book a sophrology session for adults.