Heart Rate Variability or “HRV” is a measure of the differences in time between successive heart beats and is a key metric that tracks both stress and cardiac health.
Key Points to Know about HRV:
- HRV measured regularly and tracked consistently is a good surrogate for total stress on your body.
- Big changes in HRV can be a good indicator that something needs attention.
- Tracking HRV gives you a great global insight into your current lifestyle habits and how they are impacting your health.
- From an athletic performance perspective HRV is being used by elite athletes to guide training with results outperforming conventional training programs without HRV modification.
Why is HRV important?
First of all, it is important to preface this with the fact that there is a significant individuality to HRV. So your highest possible HRV may be very low for someone else for example.
With this as context, low HRV has been associated with a myriad of maladies though, including: stress, mental health disorders like depression and anxiety, heart disease, diabetes and cancer.
History of HRV
The history of HRV is quite a fascinating and extensive one, which involves the evolution of measuring of heart rate (via pulse) and the technology required for this as a starting point and advanced mathematical principles as a current state with a view to the future. Suffice to say it is decades old and has been the source of a lot of interest, with the recent explosion in its popularity and discussion more related to accessibility (through wearables and apps) and marketing than knowledge. That said, research continues into HRV and its applications.
Neural Inputs and HRV; Understanding HRV
There are two branches of the autonomic nervous system(ANS), these are the parasympathetic nervous system (PSNS) and the sympathetic nervous system (SNS). These are often labeled via their functions of the SNS being “fight or flight” and the PSNS being the “rest and digest” system. This is a useful way to think about things for most purposes.
The heart has dual innervation, which means both systems work on it, think of it like a gas pedal and a break (the SNS being the gas pedal). To slow down you can either take your foot off the gas pedal or put your foot on the break (or both), this holds true for slowing heart rate. Reducing SNS input/drive to the heart will reduce heart rate (and this is actually the way it happens most commonly when you are exercising and your heart rate drops for example), but below a certain heart rate, there is a requirement for the PNS to actively slow the heart rate down.
This is important in understanding HRV in that a slower heart rate has a greater potential for more HRV.
So a higher HRV (with the understanding that high is relative to the individual), is indicative of less stress on the body and PNS system activation.
Measurement of HRV is sometimes glanced over, and in doing so we are doing it a disservice. Posture is quite important in HRV measurement (lying down vs sitting vs standing) and standardizing this is crucial for useful data. For most people sitting is probably ideal but some may find a better measure of stress when standing i.e. to get sensitive tracking of variations in HRV you may be best off standing for measurements. Lying down may not be particularly sensitive for some people. All of this is secondary to consistency and procedure. If you are measuring things standing, make sure you standardize standing up and measuring at the same time.
This brings up the next point of measurement. How should you take HRV? Some of this varies on purpose of using it, some on preference and some on lifestyle. There are a few broad categories of sampling; full night data (as the Oura ring does), waking sample (as many apps do) or portion of the night sample.
There is a heavy circadian nature to HRV, so this should inform your choice partly. Similarly irregular sleep patterns caused by and in addition to things like travel across time zones can really impact accuracy of overnight readings in terms of their utility in light of both circadian rhythms and sample length (with short sleep). Those who have an irregular morning routine such as people with young children, may struggle to get a good waking sample so may do better with a full night measurement.
All of this said, the most important thing is consistency of readings and method of sampling. For most people, full night, HRV data is both sensitive enough and easiest for consistency and logistics, this is why we at Hearty have chosen to use the Oura ring for this.
This is a concept which in essence pertains to the total stressors on the body, these may be physical, emotional, psychological etc. The body can (and does) adapt to stress but it does not understand the source of it, it only does its best to adapt.
So in periods of higher work or family stress, it may be valuable to consider extra stress relief/management techniques and or modifying other stressors. This concept has been really nicely illustrated in some recent researchers looking at HRV guided training programs in athletes. In some of these studies, runners only modified their training down (less intense training or day off on days with low HRV) and so overall did less training volume and intensity and yet managed a similar improvement in performance.
There are also many good anecdotal examples of people having a decreasing HRV numbers prior to illness symptoms starting, including more recent, COVID-19.
Improving HRV is possible but somewhat depends on your starting point. If you are already managing stress well and have great lifestyle habits there may not be much more improvement coming.
That said, by this far into the article you can probably appreciate that stress management/reduction is a huge part of improving HRV. Similarly, avoiding stressors such as alcohol and optimizing your sleep are two other huge aspects of improving HRV.
Diet, some supplements and weight loss have all also been shown to improve HRV.
Exercise is another key factor in improving HRV as is resonant breathing (breathing at a rate of 6 breaths per minute). Whether the effects of resonant breathing are sustained rather than just acute is hard to know though.
Key Points to Manage and Improve your HRV:
- Manage your stress
- Eat, move and sleep well
- Practice some resonant breathing or HRV Biofeedback
- Take extra time for restoration when your HRV is low
For a great breakdown of HRV, different sampling methods, use of HRV for athletes and much more, see Marco Altini’s articles here.
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