Coherent breathing and heart rate variability

What heart rate variability is

Your heart doesn't tick like a clock. The time between one beat and the next shifts a little every time. Shaffer and Ginsberg, in a 2017 overview of these measures, define it this way: the fluctuation in the time intervals between adjacent heartbeats.

There are several ways to calculate it. One, called RMSSD, sums up how much your pulse changes from one beat to the next and is used to estimate the part that depends on the vagus nerve. Another sorts the oscillations by speed: the fast ones, which travel with normal breathing, and the slow ones, which at rest reflect the baroreflex, the automatic adjustment of your pulse when blood pressure changes.

What happens at six breaths a minute

Your pulse rises a little when you breathe in and falls when you breathe out. Breathe more slowly and that swing grows. Paul Lehrer and Richard Gevirtz explain it with an idea from physics: a resonant system, stimulated at a certain frequency, answers with much larger oscillations. In the cardiovascular system, that frequency sits near 0.1 Hz, about six breaths a minute.

At that pace, they report, your pulse is exactly in phase with your breathing, and blood pressure starts to fall as soon as your pulse starts to rise. They read that second finding as a sign that the baroreflex is what amplifies the wave.

The exact point differs from person to person. The average is around 0.09 Hz, about 5.5 breaths a minute, with breaths of roughly 11 seconds. A 2006 study of 32 adults with asthma and 24 healthy adults found it was lower in taller people and in men, wasn't related to age or weight, and stayed the same across ten sessions.

Where the word coherent comes from

The name is Stephen Elliott's. His site says he introduced the method in 2005, along with the book The New Science of Breath, as a form of resonant breathing at a nominal rate of five breaths a minute. The name is a registered trademark of his company.

Labs use different words: resonance frequency breathing, or heart rate variability biofeedback when sensors are involved. On this site, Coherent breathing 5-5 runs at six a minute and Resonant breathing 5.5-5.5 uses the measured average. They're different names for the same neighborhood of paces.

What the studies show

The firmest finding is what happens during practice. A 2022 meta-analysis by Laborde and colleagues pooled 223 studies of voluntary slow breathing. It found higher vagally mediated heart rate variability while people breathed that way, right after a single session, and after multi-session programs.

On well-being, the picture is more modest. A 2020 meta-analysis pooled 58 randomized trials of heart rate variability biofeedback and found a small to moderate effect, larger against doing nothing than against another activity. Its authors caution that there were few studies for any one condition. And those are programs with sensors and coaching, not a fixed count at home.

The largest trial of coherent breathing without sensors came out in 2023. Fincham, Strauss and Cavanagh randomly assigned 400 people to breathe for four weeks at about 5.5 breaths a minute or at 12, as a placebo. Both groups improved on stress, anxiety, mood and well-being. There was no difference between them.

It also isn't clear that a longer exhale adds anything to this measure. In 2024, Meehan and Shaffer compared, at six breaths a minute, an exhale twice as long as the inhale with equal phases, in two experiments with 26 and 16 people. Variability came out the same. Earlier studies, they note, contradict one another.

What the number doesn't tell you

• Higher isn't always better. Shaffer and Ginsberg point out that some heart problems produce variability too.
• It depends on the person. It declines with age, runs higher in people with good aerobic fitness, and is lower when your pulse is fast. Comparing yourself with someone else tells you little.
• During practice, it rises because you're breathing slowly. It describes that moment. It isn't a health score or proof that something improved.
• The purpose is still an open question. Lehrer and Gevirtz suggest gas exchange is more efficient at that pace, and they write themselves that this interpretation remains speculative.

How to try it

You don't need a sensor. Start with Coherent breathing 5-5 for five minutes: five seconds in, five seconds out, through your nose, with no pauses. If five seconds feels long, begin with 4-6 breathing, which runs at the same pace with a shorter inhale. To go slower, try Resonant breathing 5.5-5.5 or 5-5-2 breathing.

Breathe slow, not huge. If you get dizzy or tingly, stop and go back to your normal pace. If you have a heart, lung or blood pressure condition, check with your care provider first. And if a watch shows an irregular pulse or you feel palpitations, that's a question for a health professional, not something to interpret with a breathing exercise.