What each one does
Coherent breathing is purely calming — equal inhale and exhale at the body’s resonant frequency. Box breathing adds two breath holds, which increases CO₂ tolerance and keeps the mind alert as well as calm.
Speed of effect
Box breathing creates a noticeable calm in 60–90 seconds. Coherent breathing builds more gradually — peak effect on HRV typically at 8–12 minutes. For an acute spike, box wins; for sustained calm, coherent wins.
HRV evidence
A 2017 study (Lehrer et al.) showed coherent breathing at resonant frequency increased HRV by 30–60% during practice. Box breathing’s evidence base is smaller but consistent for stress reduction in high-performance settings.
How to choose
If you are about to do something stressful: box. If you have 10 minutes to reset: coherent. If you are anxious about being anxious: coherent — the slower build is less likely to trigger paradoxical anxiety from over-focusing on the breath.
Log your sessions in Breathe On and explore the matching guidance at [/breathing-for/anxiety](/breathing-for/anxiety).