Everyone has a breathing rate, usually between four and a half and seven breaths a minute, at which the heart's beat-to-beat swing becomes largest and smoothest. Clinicians call it the resonance frequency and measure it with a sensor. The book's Chapter 5 explains the physiology and settles on "about six" as the pace that is close enough for almost everyone. One study asked whether close enough is actually enough.
Three groups breathed for fifteen minutes: at their individually measured resonance frequency, at one breath a minute faster than it, or not at all (sitting quietly). Then everyone did a stressful mental arithmetic task and rested. After the breathing, the resonance group reported better mood than both other groups and showed the heart-rhythm pattern that biofeedback aims for, and had lower systolic pressure during the stressor and the recovery than the quiet group. The group one breath faster landed in between and was not significantly different from either.
So the rate matters at the margin and "about six" gets you most of the way, which is what the book assumes. Two reviews of the slow-breathing literature (listed below) are the best general reading on why the pace works at all. For most people, the six-breaths-a-minute page is the practical answer; a biofeedback practitioner can find your exact number if you want it.
The studies
Steffen PR, Austin T, DeBarros A, Brown T. The impact of resonance frequency breathing on measures of heart rate variability, blood pressure, and mood. Frontiers in Public Health 5, 2017, 222. Read the abstract
- Sample
- Three groups (n not stated in abstract)
- Design
- Randomized to fifteen minutes at resonance frequency, at resonance plus one breath a minute, or quiet sitting, followed by a mental-arithmetic stressor.
- Found
- Resonance group had higher positive mood and a higher LF/HF ratio than controls and lower systolic pressure during the task and recovery; the plus-one group fell between.
- Limits
- Single session; healthy volunteers; the plus-one group did not differ significantly from either.
Zaccaro A, Piarulli A, Laurino M, Garbella E, Menicucci D, Neri B, Gemignani A. How breath-control can change your life: a systematic review on psycho-physiological correlates of slow breathing. Frontiers in Human Neuroscience 12, 2018, 353. Read the abstract
- Sample
- 15 studies
- Design
- Systematic review of slow-breathing studies measuring physiology and psychology together.
- Found
- Slow breathing (under ten breaths a minute) is associated with increased HRV and respiratory sinus arrhythmia, EEG changes, and reports of comfort, relaxation, alertness and reduced anxiety and anger.
- Limits
- Small literature; heterogeneous methods.
Russo MA, Santarelli DM, O'Rourke D. The physiological effects of slow breathing in the healthy human. Breathe 13(4), 2017, 298–309. Read the abstract
- Sample
- Review
- Design
- Narrative review of the respiratory, cardiovascular and autonomic effects of breathing at six to ten breaths a minute.
- Found
- Summarizes the mechanisms: respiratory sinus arrhythmia, baroreflex sensitivity, and vagal activity all increase at slow rates.
- Limits
- Narrative review; healthy physiology, not clinical outcomes.
Where this lands in the book
Techniques
Rooms
Two rules, no exceptions
Never practice any technique on this site while you are driving, operating machinery, or doing anything that needs your full attention. The slow ones can make you drowsy, faster than you’d expect. And never practice a breath-hold, bellows breath, or any vigorous breathing in or near water. Read Before you begin for the doctor’s list and the rest.
Verdict scale: Science means trials or meta-analyses with consistent findings; Promising means real trials that are small, few, or unreplicated; Mixed means the studies point both ways; Mechanism means it shows how something works in the body, not that it helps in life. Checked against the published abstracts in October 2026. Not medical advice.