HRV
What heart-rate variability measures, RMSSD vs SDNN, HRV-guided training studies, breathwork.
If you only read one
Heart rate recovery: the underrated 1-minute number
How quickly heart rate drops in the first minute after stopping intense exercise is a strong predictor of mortality. What the cohort data shows, how to measure it, and what counts as good.
Grade A · 3 min read · Last reviewed 2026-05-19
Breathwork and HRV: what slow breathing actually changes
Evidence BSlow breathing at around 6 breaths per minute reliably raises HRV in the short term. Here's the mechanism, what the trials measure, and the limits of what that means for long-term health.
2 min read · Last reviewed 2026-05-17
Heart rate recovery: the underrated 1-minute number
Evidence AHow quickly heart rate drops in the first minute after stopping intense exercise is a strong predictor of mortality. What the cohort data shows, how to measure it, and what counts as good.
3 min read · Last reviewed 2026-05-19
HRV-guided training: what the research supports
Evidence BUsing daily HRV to decide whether to train hard or easy is a growing practice in endurance sports. A look at the evidence for it, the limits, and the version most likely to help.
2 min read · Last reviewed 2026-05-17
Polyvagal theory: a critical look at the framework's evidence base
Evidence DPolyvagal theory is widely cited in trauma therapy, breathwork, and somatic-practice content. The specific neuroanatomical and evolutionary claims are contested by mainstream neuroscience. What the framework offers, and what doesn't hold up.
3 min read · Last reviewed 2026-05-19
Resting heart rate as a biomarker: what the cohort data shows
Evidence AResting heart rate is one of the simplest measurements with one of the largest associations with all-cause mortality. What the prospective data shows, how to track trends, and when a change matters.
3 min read · Last reviewed 2026-05-19
RMSSD vs SDNN: which HRV number means what
Evidence AThe two most common HRV metrics measure different aspects of autonomic balance. A short, practical guide to telling them apart and reading the numbers your devices produce.
3 min read · Last reviewed 2026-05-17
What HRV actually measures (and what it doesn't)
Evidence AHeart rate variability is the beat-to-beat variation in time between heartbeats. A look at what it represents physiologically, why it differs between people and devices, and what conclusions you can reasonably draw.
2 min read · Last reviewed 2026-05-17
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