Breathing rate

Each breath nudges the heart: faster on the way in, slower on the way out. That is respiratory sinus arrhythmia respiratory sinus arrhythmia Respiratory sinus arrhythmia The normal rise in heart rate as you breathe in and fall as you breathe out. It is driven by the vagus nerve and makes up much of resting HRV. More about Respiratory sinus arrhythmia , and the way you breathe changes its size.

Why it matters for HRV.

• Rate and depth change the number. Quigley and colleagues (2024) note that the breathing swing grows as breathing slows and as each breath gets deeper, whether the change is natural or paced. A slow, deep breath can raise RMSSD RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next, in milliseconds. It mainly reflects vagal activity. More about RMSSD with no change in vagal tone vagal tone Vagal tone The ongoing influence of the vagus nerve on the heart, which slows it down. It is usually estimated from HRV measures such as RMSSD and HF power. More about Vagal tone .
• The HF HF HF power The variance of the heartbeat intervals that falls in the 0.15 to 0.40 Hz band, in ms²: the range of normal breathing. It mainly reflects vagal activity when breathing is 9 to 24 breaths a minute. More about HF power band assumes normal breathing. Laborde, Mosley and Thayer (2017) give the HF band as covering breathing from 9 breaths a minute (0.15 Hz) to 24 a minute (0.40 Hz). Breathe slower and the breathing peak moves into the LF LF LF power The variance of the heartbeat intervals that falls in the 0.04 to 0.15 Hz band, in ms²: rhythms repeating every 7 to 25 seconds. Once read as sympathetic activity, which is now disputed. More about LF power band, so HF falls and LF/HF LF/HF LF/HF ratio LF power divided by HF power, with no unit. It was proposed as a gauge of balance between the sympathetic and parasympathetic systems, but research shows it cannot measure that reliably. More about LF/HF ratio rises. Quigley and colleagues use a band starting at 0.12 Hz (about 7 breaths a minute) and say the same: breathing outside the band lowers HF.
• RMSSD is less affected. Laborde and colleagues prefer RMSSD for this reason, and advise measuring breathing rather than forcing it.

Breathing from the heartbeat. Because breathing leaves a mark on the beat intervals and on the shape of the ECG ECG ECG A recording of the heart's electrical activity, taken with electrodes on the skin. ECG-based RR intervals are the reference standard for measuring HRV. More about ECG , software can estimate it without a breathing sensor. This is called ECG-derived respiration (EDR), and it is one way a device without a breathing sensor can show a respiratory rate. Lipponen and Tarvainen (2022) tested two such methods in Kubios on 262 resting and 123 exercise recordings: using both the ECG shape and the intervals worked better than the intervals alone, with an average error spread of about 4 breaths a minute.

Move the slider below from 15 to 7 breaths a minute and watch the breathing peak cross the 0.15 Hz line.

Where your breathing lands in the spectrum

A teaching model, not a recording

Power by frequency, 0 to 0.5 Hz square-root scale

VLF LF 0.15 Hz HF 0.5 Hz

Breathing rate 15 breaths a minute 4 9 (0.15 Hz) 20

Breathing peak

0.25 Hz

HF power

635 ms²

LF power

120 ms²

LF/HF

0.19

HF, normalised

84 nu

At 15 breaths a minute the breathing peak sits at 0.25 Hz, inside the HF band. HF power is 635 ms² and LF/HF is 0.19.

The slider works when JavaScript is on.

A filled spectrum from 0 to 0.5 Hz with the VLF, LF and HF bands shaded and a vertical line at 0.15 Hz. At 15 breaths a minute the tallest peak is at 0.25 Hz, inside HF, with a smaller peak at 0.1 Hz from the blood-pressure rhythm. Slide down to 6 breaths a minute and the breathing peak moves to 0.1 Hz, merges with the blood-pressure peak and towers over the rest, while the HF band empties. Readouts give the peak frequency, LF and HF power, LF/HF and HF in normalised units.

The lesson HRV, stress and breathing puts this to use.