30 days of Heart Rate Variability (HRV) Biofeedback

did you breathe today?

As calm as I can be

What’s biofeedback exactly?

In just a few words, HRV Biofeedback is a technique that consists of providing an individual with real-time feedback on instantaneous heart rate and respiration changes while being instructed to breathe at low frequencies (Lehrer and Gevirtz, 2014).

Basically, deep breathing

Morning (or night) measurements of HRV vs biofeedback: what’s the difference?

HRV analysis can be used for various applications. What we do at HRV4Training is to quantify baseline physiological stress (what we could call “chronic” stress), and how this changes in response to training and lifestyle over periods of weeks or longer. To quantify baseline physiological stress, our measurements need to be taken in a very precise moment, which is first thing in the morning (or using the entire night of data), so that we can avoid the effect of confounding factors. You can find a few examples here.

Over the years at HRV4Training we have always focused on assessing stress more than trying to improve our ability to deal with it via self-regulation, something that I am hoping to change with the new app

HRV Biofeedback is a technique that we use to improve self-regulation, and also strengthen the parasympathetic system. While our morning measurements should be done while resting and breathing naturally, during biofeedback we use deep breathing to elicit higher parasympathetic activity.

The HRV4Biofeedback app. Learn more, here

The science

As the body via the autonomic nervous system (ANS) responds to stressful stimuli in an attempt to maintain a state of balance, we can determine how effective this physiological self-regulation process is, by measuring the ANS.

During HRV biofeedback, an individual is instructed to breathe at low frequencies. Breathing at low frequencies (or deep breathing) causes large oscillations in instantaneous heart rate, which synchronize with breathing rate

The influence of breathing on heart rate is mostly modulated by the parasympathetic branch of the ANS (Lehrer and Gevirtz, 2014). Hence, deep breathing results in training of the parasympathetic system, which might explain at least part of the positive effects of HRV biofeedback reported in the literature in the context of reducing stress and anxiety (Goessl, Curtiss, and Hofmann, 2017).

Resonant frequency

As previously introduced, HRV Biofeedback requires the individual to breathe at low frequencies. Experimental studies have found the highest heart rate oscillations when breathing at approximately 0.1 Hz. This frequency is often called the resonant frequency of an individual and can vary by 0.5–1 breath/minute between individuals. The resonant frequency of an individual can be established with a protocol that consists of breathing at different frequencies for a few minutes until the frequency that elicits the maximal amplitude is found (Lehrer et al., 2003).

Resonant frequency test in HRV4Biofeedback. Learn more, here

Building a habit

Building an app is certainly easier than building a habit. While some recent attempts used protocols as short as 3 minutes per day, the original biofeedback protocols recommend two sessions of 20 minutes per day. Obviously, that’s quite a difference.

Personally, I think that we should indeed try to match what is recommended in the original protocol if we hope to see some meaningful changes. Like everything else, committing and putting the time and effort is what leads to improved outcomes, which is hardly ever the case with simple hacks

Yet, starting with very short sessions can simply be a way in. Once I got to about 10 minutes per day, it started to feel different. I was feeling the “acute benefit” of the session, as it probably was a long enough time that I could relax and de-stress. From there, I built up to about 25 minutes per day, with the occasional double session that led to the recommended 40 minutes. While I used the app on and off for several months, only in the past 30 days I made it a proper habit:

In January 2021 I went from 5-10 minutes per day of practice a few times per week to a daily 15–40 minutes of practice. While still far from the original protocol, this seems to be a reasonable ‘dose’

The data: acute vs chronic changes

As covered above in the morning (or night) vs biofeedback section, it is important to measure outside of the biofeedback session, to assess any potential benefits.

This is one of the main issues with many biofeedback studies, where changes in physiology are assessed only acutely during the practice or right after, which typically means we are seeing an HRV change due to the fact that we are deep breathing, and this change is simply a transitory change that might not really impact our physiology positively

Here is an example of my HRV during a session, as you can see the rMSSD is about 140ms, while normally at rest is not even a half of that. This means that I am doing the exercise correctly (stimulating the parasympathetic system) but it does not mean that there will be any long term effect or chronic change in my physiology:

A good session
  • night HRV averages taken with the Oura ring (the value is transformed on a logarithmic scale as we often do in research when working with rMSSD, but what matters here are relative changes)
  • baseline: blue line, 7 days moving average to better highlight the recent trend, given the typical day to day variability in HRV
  • normal values: light blue band, built using the previous 60 days of data. This is key to understand if recent (baseline) physiological changes are within our typical normal range or if we are experiencing a significant change (either a reduction below normal, highlighting higher stress, or an increase, as shown here, potentially in response to deep breathing)
Baseline trending quite a bit higher than my normal. Biofeedback effect?

Write up

Combining insights from biopsychosocial models and basic physiology, we can see how HRV biofeedback has been proposed as a technique that can help to improve emotional self-regulation and coping mechanisms via a strengthening of homeostasis, with the potential of resulting in better health and performance.

Needless to say, everybody is different. I cannot help but think that depending on for example how anxious of a person you are, you might benefit more or less from deep breathing exercises, which might explain why it seems to work for me

Get breathing!



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Marco Altini

Founder HRV4Training.com, Data Science @ouraring Lecturer @VUamsterdam. PhD in Machine Learning, 2x MSc: Sport Science, Computer Science Engineering. Runner