How to Breathe to Improve HRV: Low and Slow Breathing Improves HRV More than Deep Breathing Except When Using a Pacer

Abstract Breathing instructions and pace are used in relaxation and to improve heart rate variability (HRV). ‘Breathe deeply’ is a common instruction given in relaxation exercises; however, some argue that ‘low and slow’ breathing is more effective. No studies to date have directly tested this hypothesis in an empirical study. Using a randomized controlled design, 180 healthy college students (65% female, average BMI 23.6) were randomized into one of six conditions, breathing instructions (2 levels: deep breathing vs. low and slow breathing) and visual breathing pacer (3 levels: 12 breaths per minute control condition, no pacer condition, and 6 breaths per minute condition). After a 5-minute baseline, participants practiced breathing for 15 minutes according to their randomized condition. Following practice, participants were administered a brief stressor and ended with a 10-minute recovery period. Breathing pace, but not instructions, impacted HRV overall. The 6-breaths per minute condition showed larger increases in HRV than 12-breaths per minute and no pacer conditions. There was a significant interaction between instructions and pacer type with ‘low and slow’ instructions leading to higher HRV in the no pacer condition and ‘deep’ breathing instructions leading to higher HRV in the 6-breath condition. Given that breathing pacers are not typically used, ‘low and slow’ breathing instructions are more likely to increase HRV levels in general practice.