Slow Breathing and Stress: What HRV and Stress Resilience Can Show

Slow breathing is simple, free and recommended by health services for everyday stress. If you wear an Apple Watch, you may wonder whether a few calm minutes will show up in your numbers. HRV does tend to rise while you breathe slowly, but your daily HRV and Stress Resilience usually look much as before. This guide explains why, and how to give a breathing habit a fair trial.

What relaxation techniques can and can't do

The US National Center for Complementary and Integrative Health (NCCIH) includes breathing exercises in its overview of relaxation techniques. Their shared aim is the relaxation response: slower breathing, lower blood pressure and a lower heart rate. NCCIH regards them as safe for most healthy people and notes that the evidence varies by condition, with preliminary support for diaphragmatic breathing as a way to reduce stress. It also notes rare reports of symptoms starting or worsening in people with epilepsy, certain psychiatric conditions or a history of abuse or trauma. If an exercise leaves you more anxious or uncomfortable, stop and breathe normally.

A simple breathing practice

The NHS breathing exercise for stress works standing, lying down or sitting in a supportive chair:

1. Get comfortable and loosen any clothing that makes breathing harder.
2. Breathe low and easy, into your belly without forcing it, in through your nose and out through your mouth.
3. Count if it helps, from one to five on the way in and again on the way out. Don't worry if you can't reach five at first.
4. Continue for at least five minutes, ideally as part of your daily routine.

If each count lasts about a second, that works out at roughly six breaths a minute, a pace that matters for HRV.

On Apple Watch, Breathe sessions in the Mindfulness app last one to five minutes: you breathe in as the animation grows and out as it shrinks. Breath Rate, under Mindfulness in the watch's Settings app, sets the breaths per minute, and your heart rate appears on the summary screen afterwards.

Why HRV rises while you breathe slowly

Your heart speeds up slightly as you breathe in and slows as you breathe out, a pattern called respiratory sinus arrhythmia. A 2022 review by Sevoz-Couche and Laborde focuses on breathing at the resonant frequency, about 0.1 Hz or roughly six breaths a minute. At that pace, breathing, blood pressure and heart rhythms line up, the heart-rate swings grow larger, and vagally mediated HRV increases.

Much of that rise comes from the breathing itself. An overview of HRV measures by Shaffer and Ginsberg explains that changing your breathing rate can shift these swings a great deal without changing vagal tone. In short resting recordings, SDNN mostly reflects this breathing-linked variation, and the authors advise comparing short-term values only at normal rates of about 11 to 20 breaths a minute. A high reading during a session shows the exercise working in the moment, not a change in your baseline.

What to expect in My Bio Age

• HRV is a daily median. My Bio Age takes the median of the HRV SDNN readings in Apple Health from 9 pm to 9 pm. If one reading falls during a session, a median of several readings barely moves.
• Stress Resilience mostly compares you with your recent self. It sets your latest HRV and resting heart rate against your own seven-day averages, alongside the past week's sleep and your recent activity load. When recent readings are sparse, it falls back on a simpler HRV check and its confidence drops. It reads High from 70, Moderate from 40 and Low below that. It needs recent HRV, and it is not an input to the weekly MyBioAge Index™.
• It reflects physiology, not feelings. The score can't tell how calm or stressed you feel, so a session that leaves you calmer may not change it, and a low score doesn't mean you are stressed.
• Respiratory rate is an overnight measure. Apple Watch measures it during sleep (Apple lists it among the overnight metrics in its Vitals app), so daytime practice won't appear in it. My Bio Age takes the median of each 9 pm to 9 pm window, as it does for HRV, and it isn't part of Stress Resilience.
• Sessions aren't logged. My Bio Age doesn't read mindfulness sessions from Apple Health, so note the days you practise.

Because the reference is your own recent week, even a lasting rise in your typical HRV would show mainly on the HRV chart, while Stress Resilience settles as the averages catch up.

Build it into the day

• Choose a regular slot, such as after waking, before a demanding meeting or as part of an evening wind-down alongside these sleep habits for HRV and resting heart rate.
• Add some movement. The NHS guide to stress lists exercise among its stress busters, and an easy walk is a simple start.
• Review after two to four weeks. Compare your HRV and resting heart rate charts with the weeks before, and ask how you feel. Stress Resilience is measured against your previous week, so treat it as a day-to-day reading rather than a test of the habit. Travel, illness, workload and missing nights can move the same charts.

When stress needs more than breathing

Breathing exercises are a self-help tool, not a treatment. The NHS suggests seeing a GP if stress feels hard to manage or self-help isn't making a difference. Speak to a clinician, too, if anxiety or low mood persists or physical symptoms worry you, and don't change prescribed treatment because of a wearable reading.

If you feel you can't keep yourself safe, get help straight away. In the UK, the NHS explains where to get urgent help for mental health, including calling 999 or going to A&E if a life is at risk. Elsewhere, contact your local emergency number.

Where My Bio Age fits

My Bio Age shows HRV, resting heart rate, overnight respiratory rate and Stress Resilience together on your iPhone, which makes a few weeks of practice easier to review. The health data it uses is processed on your device.

For a calm review of your trends over the next few weeks, download My Bio Age free on the App Store and connect the Apple Health data you choose. The iPhone app is completely free, with no in-app purchases, subscription or account required. HRV and Stress Resilience are calculated privately on your iPhone; your health data stays on the device.

To go further, read how the Stress Resilience score works and what your overnight respiratory rate shows. If your HRV has dipped, start with seven checks for low HRV. My Bio Age provides general wellness information, not medical advice.