Slow breathing and shooting: Zaccaro 2018 review

This systematic review gathers what can be measured in the body and the mind when breathing slows below ten breaths per minute. From 2,461 abstracts the authors came down to 158 full texts and finally to fifteen studies, all on healthy people aged between 18 and 65, which measure a physiological parameter and a psychological outcome together. Seven studies use breathing paced by an external rhythm, five use heart rate variability biofeedback, two use Zen abdominal breathing and one a pranayama technique. Sample sizes run from 9 to 58 participants.

The picture that emerges is consistent on some points and contradictory on others. Breathing slowly, particularly at around six breaths per minute, raises heart rate variability measured as the standard deviation of the intervals and the power in the low frequency band, and raises respiratory sinus arrhythmia: all signs of parasympathetic predominance. On high frequency power, by contrast, the results point in opposite directions, with studies seeing it rise, others finding no difference and one seeing it fall. On the psychological side come greater ease, relaxation, pleasantness, energy and alertness, and less arousal, anxiety, depression, anger and confusion. On the central side, the electroencephalogram shows more power in the alpha band and less in the theta band, and the one functional imaging study included in the review finds more activity in cortical areas such as the prefrontal, motor and parietal cortices and in subcortical structures from the pons to the thalamus and hypothalamus. A single study, on ten people, finds no difference at all between slow and spontaneous breathing, which the authors put down to low statistical power.

The search was run on MEDLINE and SCOPUS, with the first query in March 2016 and the last in April 2018, combining the terms for breathing techniques with those for physiological outcomes using Boolean operators. The protocol was registered in PROSPERO and the review follows the PRISMA guidance. Two reviewers screened the abstracts independently.

The inclusion criteria are narrow, and they are the most interesting part of the method. Only techniques that slow breathing actively and directly to ten breaths a minute or fewer are admitted; practices in which breathing slows as a by-product of something else, such as transcendental meditation, yoga nidra, tai chi and qi gong, are left out, and so are mixed interventions that add postures, imagery or meditation, because in that case the effect of breathing cannot be separated from the rest. Also excluded are protocols that induce emotion, such as fear or stress induction, studies on people with an acute or chronic condition, participants under 18 or over 65, papers that measure only a physiological parameter or only a psychological outcome, single case reports and studies whose methodology is not described repeatably. The designs admitted are within-subjects, cross-sectional, randomised controlled, longitudinal and before-and-after. The original intention was a meta-analysis, abandoned because of the heterogeneity of the groups, the techniques and the outcomes.

The authors put their limits in writing, and they are substantial. The literature on slow breathing lacks any shared methodology, both in study design and in describing what the participant is actually asked to breathe, to the point that the meta-analysis was abandoned. None of the fifteen studies, with one partial exception, computes the correlation between the physiological change and the psychological one: the two levels are measured in the same people, but the link between them stays an inference. As a programme for future work the authors ask for the contribution of breathing to be separated from the other components of meditation, for both levels to be measured together so that they can be correlated, for longitudinal designs, and for the possibility of adverse effects of slow breathing to be considered.

Two further things are worth keeping in mind when reading the numbers. In most of the studies heart rate variability is measured during slow breathing rather than afterwards, and breathing at six breaths a minute amplifies the oscillations at that frequency in itself: part of the increase is a mechanical feature of the measurement. And the samples are small, from nine to fifty-eight people, mostly students or healthy adults, with no competing athletes among them. Archery, naturally, does not come up: none of the included studies concerns archers, none measures a sporting performance and none looks at what happens to a breathing technique inside a movement that has to be executed precisely. The model the authors propose at the end, with its role for the mechanoreceptors of the nasal cavity, is stated as a hypothesis to be tested.

Archers know that breathing is part of preparing the shot, and this review says what is known about that practice away from the field. Slowing the breath to around six breaths a minute shifts the balance of the autonomic nervous system measurably towards the parasympathetic side and goes, in healthy people, with more calm and less reported arousal. It is an effect in the moment, measured during or just after the exercise, in a laboratory, on participants who were doing nothing else at the time.

Getting from there to a use on the shooting line is not automatic, and the review does not make that step. None of the studies concerns archers, none measures a score, and above ten breaths a minute the effects described have not been studied. Above all, breathing at six breaths a minute means cycles of ten seconds, which fits the pause between arrows or between ends rather than the execution of the shot, which lasts a few seconds and during which the breath is held. In the registry the source counts as context from outside archery: it says that the mechanism by which slow breathing calms a person exists and can be measured, not that a breathing routine raises anyone's score.