Does heart rate variability training work?

What is heart rate variability?

Your heart does not beat like a metronome. The gaps between beats vary slightly, and that variation is heart rate variability. Higher variability generally indicates a nervous system that can shift between states, which is why it gets used as a marker of recovery and stress capacity.

Two things get called HRV training and they are not the same. One is biofeedback, where you breathe slowly while watching your heart rhythm respond in real time, usually around six breaths a minute. The other is checking a score your watch produced overnight. Only the first has been trialled properly.

Does biofeedback training work?

The evidence supports it. A 2021 meta-analysis of 14 randomised controlled trials covering 794 adults found heart rate variability biofeedback reduced depressive symptoms at Hedges' g = 0.38, a medium effect that reached significance.

Pizzoli and colleagues published this in Scientific Reports. The effect held across varied groups including people with cardiovascular disease, people with cancer, people with stress disorders, and non-clinical samples, which is a useful sign of robustness.

Heterogeneity was moderate at 45 per cent and dropped once publication year and measurement instrument were accounted for. The authors note depression was measured only by self-report questionnaire, that effect sizes varied considerably depending on which scale was used, and that there is not enough evidence to say who benefits most or which protocols and devices work best.

What is the practice actually doing?

Breathing at roughly six breaths a minute puts your breathing in step with a natural rhythm in your blood pressure control, which produces large swings in heart rate that show up as high variability. The feedback screen makes that visible, so you can find and hold the pattern.

Worth noting what appeared elsewhere in this literature. When researchers added ear-based vagus nerve stimulation on top of slow breathing, the stimulation added nothing while the slow breathing raised variability on its own. The breathing is doing the work.

What is your wearable actually telling you?

Considerably less than it implies. Overnight HRV varies with sleep, alcohol, illness, hydration, room temperature, position and the device itself, so a single morning number carries a lot of noise and very little signal.

Trends over weeks are more meaningful than any day. A sustained drop alongside poor sleep and heavy training is worth attending to; one low reading after a late night is simply a late night.

Absolute numbers between people mean almost nothing. Variability falls with age and differs enormously between individuals, so comparing your score to someone else's is not a comparison of anything useful.

Is it worth doing?

If you want the version with evidence, practise slow breathing at around six breaths a minute for ten to twenty minutes, and use feedback if you have it. Feedback helps you find the rhythm, and the breathing is the active part.

If you are tracking rather than training, hold the number loosely. Watch the trend, use it as one input alongside how you feel and sleep, and be aware that a poor score can raise the anxiety it is supposedly measuring.

Sleep, exercise and alcohol move heart rate variability more than any breathing protocol. If the goal is a better number, those come first.