Objectives
Here, we planned to evaluate the effects of CB on stress, mental health, sleep and wellbeing outcomes in the (to the best of our knowledge) first robust RCT, comparing CB (at ~ 5.5 bcpm) to a well-designed placebo (12 bcpm with equal inhale:exhale ratios and no pauses). 12 bcpm is the lower bound of average resting respiration rate in adults. The theoretical rationale for our study was identifying whether CB exerts specific effects in a well-designed RCT within a large general population sample. Whilst two recent reviews have shown promise for the effects of slow breathwork, they have also highlighted the risk of bias in studies to dateFundamentally, we also set out to design a high-quality placebo for RCTs using CB which allows controlling for qualities such as attention, credibility and expectation. Since we were studying breathwork, we could manipulate the key variable of breathing pace, whilst keeping the remaining variables (i.e., duration, instruction) constant. Our intervention and placebo audio guides were identical (same background sound, and guidance to pace breathing), except for the speed at which participants were instructed to breathe. Accordingly, another important outcome from this study was whether we were able to create a much-needed placebo, which is not experienced differently from CB on credibility and expectancy (as well as being matched for duration and adherence), therefore potentially isolating the specific active ingredient of CB pertaining to this technique for future RCT research on mental health outcomes. This also enabled participant blinding to intervention allocation to be possible, very difficult to achieve in behavioural intervention studies.