Heart rate variability (HRV) is one of the most reliable indicators of your autonomic nervous system. A healthy heart doesn't beat like a metronome: the interval between beats varies constantly. The higher this variability, the more flexible your nervous system and the better it switches between effort and recovery.

HRV: a window on the autonomic nervous system

The autonomic nervous system has two sides: the sympathetic (acceleration, 'fight or flight') and the parasympathetic (recovery, return to calm). HRV reflects their dynamic balance. Chronic stress tends to lock the body in sympathetic mode, with low HRV.

What the meta-analyses show

HRV biofeedback training is associated with reduced stress and anxiety with a large effect (Hedges g ≈ 0.83) — one of the most reproducible findings in the mind-body literature.

Key data

g ≈ 0.83
Effect on stress & anxiety
Goessl et al. (2017) meta-analysis: the effect size of HRV biofeedback on self-reported stress and anxiety is about 0.83 — a large effect by statistical conventions.
58 studies
Systematic review
Lehrer et al. (2020) confirm that the strongest effects concern anxiety, mood and performance; effects are more modest on sleep and quality of life.

How it is trained in practice

We measure your heart rhythm in real time and a visual guide paces your breathing at about six cycles per minute — the cardiovascular 'resonance frequency'. At that rhythm, HRV amplitude increases and the baroreflex is engaged. Session after session, the nervous system relearns to return to calm faster.

At Superhuman Wellness

We measure your HRV at the start to set a baseline, then calibrate the training (biofeedback and cardiac coherence) to your individual resonance frequency.

Sources
Goessl V.C. et al., Psychological Medicine, 2017 (PMID 28478782).
Lehrer P. et al., Applied Psychophysiology and Biofeedback, 2020 (PMID 32385728).
Lehrer P. & Gevirtz R., Frontiers in Psychology, 2014.