HRV biofeedback and shooting, the theory: Lehrer 2014

This is not an experimental study but a hypothesis and theory article: two leading researchers in heart rate variability biofeedback summarise the mechanisms by which, in their view, the technique works. Biofeedback means breathing slowly while watching the heartbeat on a screen beat by beat, trying to make the oscillations linked to breathing larger and more regular: the heart speeds up on the in-breath and slows on the out-breath.

The central argument is that at around six breaths a minute (0.1 Hz; on average 0.09 Hz, or 5.5 breaths a minute with breaths of about 11 seconds) the cardiovascular system resonates. At that frequency heart rate and breathing move in phase, heart rate and blood pressure in opposition, and the baroreflex, which adjusts heart rate when pressure changes, amplifies the oscillations. The authors report that baroreflex gain rises sharply during practice, and that after about three months of practice twice a day it rises at rest as well. As a second mechanism they propose the nerve pathways running from the body to the brain through the vagus, citing two studies from their group in which the heartbeat evoked potential changed during slow breathing and after biofeedback training.

The article has no sample of its own and no systematic literature search. It brings together work by Lehrer's and Vaschillo's groups on the relationship between breathing, heart rate and blood pressure, animal experiments on gas exchange in the lungs at different phase relationships between heart rate and breathing, and two recent studies from Gevirtz's group on the heartbeat evoked potential, recorded with scalp electrodes. In the first, the potential was more pronounced during slow breathing than at rest or during induced emotions; in the second, 12 people trained with biofeedback over four sessions showed greater heart rate variability and a change in the potential, which did not appear in 13 people trained in relaxation with muscle (EMG) biofeedback.

The applications mentioned come from an earlier review by Gevirtz and are almost all clinical. Sport appears in a few lines, with three references to work on athletic performance; archery is never mentioned.

The authors themselves call several steps speculative: the purpose of the phase lag between heart rate and breathing, the role of the vagus in emotion, and the other mechanisms listed at the end (a meditation-like effect, distraction from worries, effects on inflammation). Much of the evidence comes from the authors' own laboratories and the choice of studies follows no stated criteria, so the article tells us how its authors read the field, not how much the field has demonstrated. For many applications, they write, controlled studies are still few.

For archery the whole middle step is missing: no data on archers, no measure of accuracy or score, nothing on what happens when slow breathing meets the rhythm of an end and the way an archer manages their breath while aiming.

This article explains why slow breathing turns up so often in mental preparation, archery included: it sets out the resonance mechanism at around six breaths a minute and why that rhythm produces the largest heart rate oscillations. It does not show that biofeedback improves shooting. The step from physiology to performance, and to aiming in particular, has to be looked for in studies on archers, which the registry links to the same research line.

Anyone practising slow breathing with an app or a heart rate strap will find the reasoning behind the method here, not evidence of an effect in competition. The clinical applications the article discusses lie outside the scope of this registry.