Breathing practices have moved from yoga studios into general wellness, sports performance and clinical settings, under the broad label of breathwork.
The label covers practices with quite different physiological effects and quite different evidence, and separating them is worth doing.
Slow breathing
The best-supported category. Breathing at a reduced rate, typically around six breaths per minute, frequently with a longer exhalation than inhalation.
The mechanism is reasonably well understood. Breathing rate influences autonomic balance through several pathways, including the baroreflex and respiratory sinus arrhythmia — the natural variation in heart rate across the breath cycle.
At around six breaths per minute, this variation reaches a resonance where heart rate oscillation is maximised, which is the basis of heart rate variability biofeedback.
Evidence: reasonable for acute reductions in physiological arousal and subjective anxiety, and some evidence for blood pressure reduction with sustained practice. Trials are generally small and the direction is consistent.
Practically: this is the version to use if you want an evidence-informed technique for acute stress. Slow the breath, make the exhalation longer than the inhalation, continue for a few minutes.
Extended exhalation specifically
A frequently cited detail with a plausible basis. Parasympathetic influence on the heart is greater during exhalation, so lengthening it shifts the balance.
Various specific patterns circulate with particular ratios. Evidence for any specific ratio over another is limited; the general principle of a longer exhalation is better supported than any particular number.
Nasal breathing
A distinct claim with partial support.
Nasal breathing filters, humidifies and warms air, and produces nitric oxide in the nasal passages which has vasodilatory effects in the lungs.
Evidence for chronic mouth breathing being associated with problems — particularly in children, where it's linked with dental and facial development issues and with sleep-disordered breathing — is reasonable.
Evidence for switching to nasal breathing during exercise improving performance is weaker and mixed. Some studies find no benefit and increased perceived exertion.
The reasonable position: nasal breathing at rest is preferable, chronic mouth breathing is worth investigating for an underlying cause, and claims about athletic performance are not well established.
Hyperventilation-based practices
Practices involving periods of rapid deep breathing followed by breath holds. These have become popular and require a specific safety caution.
The physiology: rapid deep breathing reduces blood carbon dioxide, which raises blood pH and reduces the urge to breathe. It also causes cerebral vasoconstriction, which is why people commonly experience tingling, light-headedness and altered sensation.
The reduced drive to breathe permits a longer breath hold, which is why the technique produces impressive-seeming breath hold times.
The danger is specific and serious: this substantially increases the risk of loss of consciousness. In water, that means drowning. There are documented deaths from hyperventilation before breath-hold diving, and organisations in that field warn against it explicitly.
Anyone practising these techniques should do so sitting or lying down, never in or near water, never while driving, and never alone if new to it.
Evidence for claimed benefits — on immune function, on inflammation, on stress resilience — exists in some small studies and is preliminary. Whatever the merits, the safety point stands independently.
Breath holding for performance
Practices involving repeated breath holds, sometimes framed as altitude simulation.
The comparison to altitude training is not accurate. Altitude exposure involves sustained reduction in oxygen availability producing adaptations over weeks. Brief breath holds produce transient changes and quite different physiology.
Some evidence exists for specific effects on spleen contraction and haematocrit, and translation to meaningful performance improvement is not established.
Clinical breathing training
Worth distinguishing from wellness applications. Breathing retraining is used clinically for specific conditions.
Dysfunctional breathing patterns, including breathing pattern disorders, are recognised clinical entities treated by physiotherapists with specific training.
Breathing exercises are used in asthma management as an adjunct, with some evidence for symptom and quality of life improvement, and not as a replacement for prescribed medication. That distinction is critical and has been the subject of serious harm where it's been ignored.
Pulmonary rehabilitation for chronic lung conditions includes breathing techniques with a solid evidence base.
What I'd take from this
Slow breathing with extended exhalation is free, safe for nearly everybody, has plausible mechanisms and reasonable evidence, and takes two minutes. That's a favourable proposition regardless of effect size.
Nasal breathing at rest is sensible. Chronic mouth breathing is worth investigating.
Hyperventilation practices require genuine caution and should never be done in water.
And anyone with a respiratory or cardiac condition should discuss breathing practices with their clinician rather than starting from a video, particularly where a practice is being suggested as an alternative to prescribed treatment. It isn't.
General information only. Anyone with a respiratory or cardiovascular condition should consult a healthcare professional before beginning breathing practices.
What to do in an acute moment
Since this is the most common practical use, a concrete version. Slow the breath deliberately. Make the exhalation roughly twice as long as the inhalation. Breathe through the nose if that is comfortable. Continue for two to three minutes.
Two things help. Practising it before you need it, so the pattern is familiar rather than another thing to work out under pressure. And not expecting it to remove the feeling — it reduces physiological arousal modestly, which is enough to make a difficult moment more manageable and is not a switch.