Systematic Review of Randomised Controlled Trials Evaluating Box Breathing for Stress, Autonomic, and Clinical Outcomes.

Box breathing, also referred to as square breathing or four-square breathing, consists of equal phases of inhalation, breath retention, exhalation, and post-exhalation hold. It is widely promoted as a simple breathing technique for stress reduction and autonomic regulation; however, evidence from randomised controlled trials (RCTs) specifically evaluating box breathing remains limited and fragmented.To systematically identify and synthesise evidence from randomised controlled trials assessing the effects of box breathing on stress-related, autonomic, and selected clinical outcomes. This systematic review was conducted in accordance with PRISMA 2020 guidelines. Electronic databases including PubMed, Scopus, Web of Science, and ClinicalTrials.gov were searched for randomised controlled trials published up to 2025. Studies were included only if they explicitly investigated box breathing (equal-phase inhale-hold-exhale-hold pattern) as the primary intervention. Data extraction and methodological quality assessment were performed using the Cochrane RoB 2 tool. Due to substantial heterogeneity in populations, interventions, and outcome measures, findings were synthesised narratively. A total of eight eligible randomised controlled trials that were eligible were found. The studies encompassed both healthy adults and clinical cases such as postpartum women and women recovering from surgery. In several studies, box breathing was shown to have short-term benefits on perceived stress, perceived anxiety and mood in a non-uniform manner. There were also mixed physiological responses, s with decreases in respiratory rate seen in some studies and changes in heart rate and heart rate variability in others. There is also more recent evidence that box breathing reduces certain acute stress responses, such as heart rate, state anxiety and salivary alpha-amylase, but not HRV or cortisol. Clinical results were a decrease in postpartum pain and an enhancement in some lactation-related outcomes. Of the 29 RCTs, there were no RCTs that directly measured spirometric lung function or maximal aerobic capacity. Randomised studies in the literature have been conducted in recent years to evaluate the efficacy of box breathing on a wide range of autonomic functions; although it appears to be effective for short-term stress and emotional self-regulation, its effects on wider autonomic functions are inconsistent. The evidence available is limited due to a small number of studies, variable protocols and populations, and a limited long-term assessment. More carefully conducted randomised trials with uniformly prescribed breathing regimens and physiological measures of outcome are needed before more widespread clinical uses can be determined.