# Box breathing or six breaths per minute: Which strategy improves athletes post-HIIT cardiovascular recovery? PMID: 41248139 Journal: PLOS ONE Published: 2025-11-17 Authors: Kasap M, Aydin GR ## Question Do box breathing, six breaths per minute, and spontaneous breathing differ in their acute effects on post-HIIT heart-rate recovery and perceived exertion? ## Summary In physically active sports science students, three post-HIIT breathing strategies were compared in randomized crossover order. Six breaths per minute looked less stressful than box breathing: box breathing produced higher final heart rate and higher perceived exertion, while recovery time to baseline heart rate did not differ significantly. The study was acute and limited to young active students. ## Population - Forty Bartin University sports science students: 25 male and 15 female; age 20.95 +/- 1.75 years; BMI 22.97 +/- 3.25 kg/m2. Participants were athletes/physically active at least two days per week, familiar with cycle ergometer training, and had no known cardiopulmonary or orthopedic disorders or prior/current breathing/meditation practice. - Sample size: 40 - Age: 20.95 +/- 1.75 years - Sex: 25 male, 15 female - Fitness level: Physically active sports science students/athletes - Health status: No known cardiopulmonary or orthopedic disorders ## Methodology - Randomized crossover acute study - Three acute sessions separated by at least 48 h - Spin bike room - Randomized and controlled study design. ## Protocol - Spin-bike HIIT plus guided recovery breathing; details: Each participant completed spin-bike HIIT with 10 min warm-up and 15 min of 30 sec work/60 sec recovery at 85-95% estimated HRmax. During recovery, participants performed one of three randomized breathing protocols: spontaneous breathing, box breathing with 4 sec inhale/hold/exhale/hold, or 6 breaths/min with 5 sec inhale and 5 sec exhale. Visual and audio cues guided breathing and researchers monitored chest movement. - Modality: Spin-bike HIIT with recovery breathing protocols. - Work intervals: 30 sec. - Recovery: 60 sec guided breathing/rest. - Sets or repetitions: Repeated 30 sec work/60 sec rest cycles over 15 min. - Intensity: 85-95% estimated HRmax at constant 100 W resistance. - Session duration: 15 min HIIT main exercise plus 10 min warm-up; recovery monitored until baseline HR returned. - Program length: Three acute sessions separated by at least 48 h. - Progression: No progression; crossover acute protocol. - Within-participant spontaneous, box, and 6 bpm breathing protocols; details: Within-participant crossover comparison among spontaneous breathing control, box breathing, and 6 breaths/min breathing; each session separated by at least 48 h. - Modality: Spin-bike HIIT with recovery breathing protocols. - Work intervals: 30 sec. - Recovery: 60 sec guided breathing/rest. - Sets or repetitions: Repeated 30 sec work/60 sec rest cycles over 15 min. - Intensity: 85-95% estimated HRmax at constant 100 W resistance. - Session duration: 15 min HIIT main exercise plus 10 min warm-up; recovery monitored until baseline HR returned. - Program length: Three acute sessions separated by at least 48 h. - Progression: No progression; crossover acute protocol. ## Outcomes ### Final heart rate Status: mixed Final HR differed by breathing protocol: spontaneous 159.05 +/- 10.38 bpm, box breathing 164.65 +/- 9.40 bpm, 6 bpm 154.77 +/- 12.18 bpm; repeated-measures ANOVA p<.001. p<.001 ### Box breathing final heart rate Status: improved Box breathing had higher final HR than 6 bpm by +9.87 bpm (95% CI 6.32 to 13.42; p<.001). 95% CI 6 ### Heart-rate recovery time Status: no clear change Return time to baseline HR did not significantly differ: spontaneous 703.05 +/- 202.71 sec, box 753.02 +/- 150.60 sec, 6 bpm 675.70 +/- 157.24 sec; p=.128. p=.128 ### Perceived exertion Status: mixed RPE differed by protocol: spontaneous 15.25 +/- 1.35, box 17.27 +/- 1.30, 6 bpm 15.25 +/- 1.08; p<.001. p<.001 ### Box breathing perceived exertion Status: improved Box breathing produced higher RPE than both 6 bpm and spontaneous breathing; both p<.001. p<.001 ## Practical Insights - Post-HIIT breath-hold box breathing may be counterproductive for immediate recovery comfort. - A simple 5-sec inhale/5-sec exhale rhythm is easier to translate into app cues and was less stressful than box breathing. - Do not promise faster HR recovery time from 6 bpm breathing because recovery time did not significantly differ. ## Limitations - Acute single-application effects only; long-term adaptation unknown. - Young healthy physically active sports science students limit generalizability. - No HRV, end-tidal CO2, or respiratory-rate monitor outcomes. - Bike-based and guided setting may not generalize to unsupervised app use. ## Safety And Adherence - No adverse events were reported. - Box breathing increased physiological/perceptual stress compared with 6 bpm in this post-HIIT context. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/41248139/) (pubmed) - [DOI](https://doi.org/10.1371/journal.pone.0336615) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12622787/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.