Tracking the Oura HRV Coefficient of Variation (HRV CV)

Tracking the Oura HRV Coefficient of Variation (HRV CV)

Written by Andrew Flatt, Dave Korsunsky and Chuck Hazzard


We’ve released an experimental feature in Heads Up Health which automatically calculates the HRV coefficient of variation (CV) based on the data from your Oura ring.

Why track HRV CV?

Looking at daily HRV readings enables you to note short-term fluctuations relative to your baseline. This can be useful for observing the effects of various stressors and lifestyle factors which can help inform on behavior-modification strategies to optimize your HRV.

Due to daily fluctuations, an isolated (i.e., single time-point) HRV measure may not truly reflect an individual’s typical HRV. Thus, some researchers and practitioners are moving towards averaging a series of daily measures to better characterize one’s autonomic activity. In turn, most HRV apps are now reporting a rolling weekly average of your HRV values.

Tracking the rolling weekly average provides a better indication of whether your HRV is actually changing in a given direction. In addition, instead of reacting to an isolated change in HRV, a more conservative and convenient approach would be to react only when the rolling average starts to change. One low HRV reading may not be of much concern and would have little impact on the weekly average. However, a series of low scores will reduce the rolling average and may indicate that it’s time to do something about it.

Along with your rolling weekly HRV average, further insight can be gained by monitoring the Coefficient of Variation (CV) among the rolling HRV values. This is because the magnitude of HRV fluctuations can change from week to week, with or without out much change in the rolling average. How much your HRV fluctuates on a day-to-day basis is quite meaningful. Large fluctuations increase the CV while smaller fluctuations lower it.

Interpreting HRV Coefficient of Variation (HRV CV) values

Typical HRV CV values range from 2 – 20%. If we were to take a random sample of adults and measure their HRV for a week, we would probably find that individuals who are younger, healthier (i.e., without disease), leaner and more aerobically fit will fall on the lower end of that range and less-healthy individuals on the higher end.

Regardless of what your CV is at a given time, it’s important to know that it can and will change. Now, whether an increase or decrease in your CV should be interpreted as good or bad is entirely context-dependent. We’ll use some practical examples to explain.

Among healthy individuals, an increased CV is typically associated with greater stress, fatigue, and lower fitness. Vice versa for a lower CV. Thus, the CV is a useful value for assessing adaptation to a new fitness program or lifestyle change. For example, unfamiliar stress will typically cause greater fluctuations in HRV (i.e., increased CV). However, as you become familiar with the new routine, there should be less fluctuation (i.e., decreased CV) which is a sign of positive adaptation. What was once quite stressful to your body is no longer as stressful.

Reductions in the CV are typically good, indicative of increasing fitness, lower stress (or improved stress tolerance) and so forth. There are exceptions, however. For example, suppose your new training program or work schedule is overbearing. Accumulating stress causes an initial increase in your CV. As things continue, your healthy eating habits start to wane, your sleep deteriorates and you become rundown. In this context, your HRV readings may become chronically suppressed, failing to bounce back to baseline. Thus, your rolling average has now decreased, as has your CV.

How we calculate Oura HRV CV

At the time of this post, Oura currently does not report the HRV CV in their app. Thus we are calculating this in Heads Up Health using the average HRV value during the sleep cycle as reported by the Oura app:

Oura HRV Coefficient of Variance (CV)

Figure 1: Oura HRV Average

Using these average HRV values we then calculate the Oura Coefficient of Variation (HRV CV) as follows:

  • Calculate the natural logarithm (ln) value of the nightly HRV average as reported by the Oura app (figure 1)
  • Calculate the mean and standard deviation from the prior 7-day HRV values
  • Divide the standard deviation by the mean
  • Show as a percentage

Note: Some experts in the field have suggested a more accurate method would be to look at the Oura HRV readings from the deep (slow wave) sleep states or by looking at the HRV readings just prior to waking. We are open to changing our approach here based on feedback from users. Feel free to send us your comments.

Tracking Oura CV in Heads Up Health

You can now add the Oura CV metric onto your Heads Up Health dashboard:

Add the Oura HRV CV to your dashboard

Figure 2: Add the Oura HRV CV to your dashboard

You can also graph this marker on the Analyzer next to any other health metric to explore your own correlations:

Compare your Oura HRV CV metrics on the Analyzer

Figure 3: Compare your Oura HRV CV metrics on the Analyzer

Moving the needle

Why would these numbers increase or decrease? The CV reflects the fluctuation in your day-to-day HRV over the last 7 days. High or low HRV readings relative to your baseline will, therefore, contribute to a higher CV whereas more consistent or stable HRV readings will contribute to a lower CV.

Why is lower better?

When the rolling average is stable or increasing, a lower CV reflects less disturbance in autonomic homeostasis. This may mean that you are experiencing less stress or simply coping with it better.

The CV must always be interpreted in context. For example, a night of high-quality sleep may increase HRV well-above baseline, contributing to a higher CV. In a situation like this, the elevated CV is obviously not reflecting higher stress. In addition, stress is important as it stimulates adaptation. Therefore, an increased CV is a normal response to a greater or novel stimulus. However, repeated exposure and adaptation to the stimulus should provoke smaller HRV fluctuations over time and therefore a lower CV. Here, the reduced CV reflects an improved ability to tolerate and recover from the stressor and thus a capacity for greater stress.

Important lifestyle factors which can affect HRV CV

Any factor that alters HRV from baseline contributes to an increased CV. Common factors that affect HRV include:

  • Travel/jet lag
  • Physical stress such as high-intensity exercise
  • Mental and emotional stress
  • Over-training / injury
  • Sleep quality and quantity
  • Illness
  • Drastic changes to daily routines
  • Pain
  • Blood sugar fluctuations
  • Hydration

Heads Up Health can help you holistically track these other lifestyle factors to help identify areas that need attention.


The HRV CV is another powerful biomarker we can use to further understand how we are managing the stressors in our daily lives. Heads Up Health now supports this metric. This is an initial implementation and we will further refine this feature as required.

Ready to start tracking your Oura HRV CV? Start your free trial using the button below!


References and Recommended Reading on the CV

Flatt, A.A. Improving HRV Data Interpretation with the Coefficient of Variation

Buchheit, M., Mendez-Villanueva, A., Quod, M. J., Poulos, N., & Bourdon, P. (2010). Determinants of the variability of heart rate measures during a competitive period in young soccer players. European journal of applied physiology, 109(5), 869-878.

Flatt, A. A., & Howells, D. (2019). Effects of varying training load on heart rate variability and running performance among an olympic rugby sevens team. Journal of science and medicine in sport, 22(2), 222-226.

Flatt, A. A., Esco, M. R., Allen, J. R., Robinson, J. B., Earley, R. L., Fedewa, M. V., … & Wingo, J. E. (2018). Heart rate variability and training load among national collegiate athletic association division 1 college football players throughout spring camp. The Journal of Strength & Conditioning Research, 32(11), 3127-3134.

Flatt, A. A., & Esco, M. R. (2016). Evaluating individual training adaptation with smartphone-derived heart rate variability in a collegiate female soccer team. The Journal of Strength & Conditioning Research, 30(2), 378-385.

Flatt, A. A., Hornikel, B., & Esco, M. R. (2017). Heart rate variability and psychometric responses to overload and tapering in collegiate sprint-swimmers. Journal of science and medicine in sport, 20(6), 606-610.

Flatt, A. A., Esco, M. R., Nakamura, F. Y., & Plews, D. J. (2017). Interpreting daily heart rate variability changes in collegiate female soccer players. J. Sports Med. Phys. Fitness, 57, 907-915.

Flatt, A. A., & Esco, M. R. (2015). Smartphone-derived heart-rate variability and training load in a women’s soccer team. International journal of sports physiology and performance, 10(8), 994-1000.

Nakamura, F. Y., Pereira, L. A., Rabelo, F. N., Flatt, A. A., Esco, M. R., Bertollo, M., & Loturco, I. (2016). Monitoring weekly heart rate variability in futsal players during the preseason: the importance of maintaining high vagal activity. Journal of sports sciences, 34(24), 2262-2268.

Plews, D. J., Laursen, P. B., Kilding, A. E., & Buchheit, M. (2012). Heart rate variability in elite triathletes, is variation in variability the key to effective training? A case comparison. European journal of applied physiology, 112(11), 3729-3741.

Tonello, L., Reichert, F. F., Oliveira-Silva, I., Del Rosso, S., Leicht, A. S., & Boullosa, D. A. (2016). Correlates of heart rate measures with incidental physical activity and cardiorespiratory fitness in overweight female workers. Frontiers in physiology, 6, 405.

Product updates

Oura Temperature Deviation (3/16/18):

We’ve added support for tracking core temperature deviation from the Oura ring. You can now add this metric to your dashboard and see how it correlates with other biomarkers:

Oura temperature deviation

Oura temperature deviation

Tracking Body Tape Measurements

Tracking Body Tape Measurements

For many people, using periodic tape measurements is much more effective than a typical scale for tracking changes in body composition.

We will cover the best practices for effectively using body tape measurements in this post.

You can track your body tape measurements alongside all your other vital health metrics using the Heads Up app. Get started using the button below. Or, read on to learn the basics of using the tape measure to track your body composition!


Why Track Body Tape Measurements?

Scales don’t tell the full story

In many cases, you may be adhering to a well-designed nutrition and exercise plan but weight on the scale is not coming down the way you would like (it may even be increasing…). However, you notice your clothes are starting to fit better and you are looking and feeling thinner and more energetic.

This is a common scenario. Although the absolute number on the scale isn’t moving the way you’d like, your body composition is indeed improving dramatically as fat is lost and lean muscle is gained. Body tape measurements are an excellent way to understand how your body composition is improving in these scenarios.

Track muscle development

If strength training is part of your regimen, body tape measurements are a great way to understand which muscle groups are growing and which may need to be attacked differently.

Track your progress over time

One of the most rewarding parts about making healthy lifestyle changes is having a record of your progress over the course of months or even years so you can see how far you’ve come.

Compare with other metrics

Body tape measurements are a great way to understand *where* you are gaining, but it is also important to know *what* your are gaining. Thus, we also recommend tracking body fat percentage so you can determine if the gains are from muscle or fat.

Additionally, Heads Up can help you compare your body tape measurements with all other health and fitness data (blood sugar, diet, exercise etc.) so you have a complete picture of how your lifestyle choices are affecting body composition.

How to track body tape measurements with Heads Up

Step 1: Enter measurements

To get started, simply add the ‘Measurements’ tile to your dashboard so you can track these values alongside other important health metrics:

Add e

Add measurements to your dashboard

Then simply use the ‘+’ button on the measurements tile to add new measurements:

body tape measurements add

Enter your body tape measurements

Step 2: Track progress

Using the Heads Up app, you can graph your measurements over time to track your progress.

You can also graph your measurements together with other health metrics.

For example, it is well known that lowering blood sugar is an extremely effective way to lose weight. In the graph below, we can see how blood sugar and ketones, which sync automatically from the Keto-Mojo meter, compare to body tape measurements.

body tape measurements analyzer

Compare measurements with ketones and blood sugar from the Keto-Mojo meter.

Step 3: Re-measure every few weeks

Periodically re-measure so you can correlate changes with your diet, exercise and lifestyle.

Best practices for body tape measurements

A few tips to ensure you are getting the most out of the body tape functionality in Heads Up:

  1. Consistency: Your goal with body tape measurements is consistency. The tape should be pulled to where it is lying flat against the skin all the way around. The pressure you put on the tape isn’t that important; it is only important that it is the same every time you do it. Use the same process every time you measure to ensure accurate results.
  2. Dominant side: For measurements such as bicep, forearm, calf and thigh, we recommend using your dominant side to collect measurements.

That’s it! You can create your Heads Up account and start tracking measurements using the button below.

If you’ve got comments, questions and/or feedback on how we can improve this feature, please contact us.


Customizing Lab Ranges in Your Heads Up Profile

Customizing Lab Ranges in Your Heads Up Profile

Customizing lab ranges is a unique feature that allows you to tailor your Heads Up profile to meet your specific needs (skip to the end of this post for a link to the video tutorial). If you’ve been tracking lab values in your Heads Up profile, you’ve noticed that we provide standard reference ranges for each lab test. These are the same ranges used by most conventional doctors and labs in the US.

Once you connect a medical facility or manually enter your own test results (see this video for instructions), we will also match your personal results against the standard ranges using a green (low risk), yellow (moderate risk) and red (high risk) color coding system. Here’s an example of what this looks like for a typical cholesterol panel:

Tracking lab values in your Heads Up profile

Tracking lab values in your Heads Up profile

This works fine for most general use cases but there are some good reasons why customizing lab ranges may be necessary.

1. Functional vs. Pathological ranges

Conventional medicine typically relies on what are known as a ‘pathological ranges’ for interpreting lab test results. The pathological range is used to diagnose disease. If your personal results fall outside of the pathological range, it usually indicates the potential for disease is present.

Functional ranges take a slightly different approach. They are designed to catch risk before it progresses into a pathological range. For example, the pathological range for fasting glucose may be 65-110 mg/dL whereas the functional range might be 85-100 mg/dL. If your own personal result came back at 105 mg/dL, you would be considered ‘normal’ according to pathological ranges, but a functional range would flag that result for potential early intervention/treatment.

Many health practitioners prefer to work with functional ranges. Customizing lab ranges gives you the ability to decide which approach (functional or pathological) best matches your health goals and customize your Heads Up profile accordingly.

2. Limitations of the standard bell curve

The pathological lab values provided with typical lab tests are actually based on a “bell curve analysis” of all the people that have been to the lab over “x” amount of time (usually in the past year).

The problem with using a bell curve to set reference ranges is that the sicker the population gets, the wider (and less useful) the lab reference ranges become. It may be necessary to look at functional ranges so you are not considered “normal” or “healthy” simply because your lab tests fall in the same range as the majority of the sick people that have been to that lab.

3. Customizing to your personal needs

You may also need to customize lab ranges based on your own personal needs. Factors such as genetics, ethnicity, medications and diet (paleo, keto, vegan etc.) may dictate that lab ranges need to be tailored to your own body and lifestyle choices.

For example, individuals on low-carb/high-fat diets (paleo, keto etc.) tend to have much higher ‘Total cholesterol’ and ‘LDL cholesterol.’ In many cases, these numbers may fall outside the pathological range and would be flagged as a risk factor. However, these same individuals also tend to have much higher ‘HDL cholesterol’ and much lower ‘triglycerides’ and taken as a whole, their cardiovascular risk is very low. By working with a trained health practitioner, you can define ranges that match your specific circumstances

Customizing lab ranges

You can edit the default values in Heads Up to enter your own custom ranges (see video tutorial below). Once saved, the color coding will automatically update based on your newly defined values. Here are some of the permitted values for custom lab ranges:

  • Ranges: The easiest solution is to just enter ranges (e.g. 0-200).
  • Greater than, less than, equals: You can use the greater than (>) or less than (<) symbols and combine them with ‘equals’ (=) to define your ranges (e.g. >200).
  • Multiple ranges using ‘OR’: You can also list multiple ranges using the ‘OR’ operator (e.g. <100 or >= 200)

The example below shows how you can customize a reference range in your own profile based on the options above.

Customize lab ranges in Heads Up Health

Customize lab ranges in Heads Up Health

Note 1: You can choose to omit a certain risk profile if you choose. For example, many users will choose to omit the ‘moderate’ risk section and only enter values for ‘low risk’ and ‘high risk.’ This is permitted and we will simply omit colors for any values within a range that has not been set.

Note 2: If you make a mistake, you can use the ‘reset’ link to restore the default values.

If you have any questions, comments or concerns on customizing lab ranges, let us know. You can also reference the video below for specific instructions. If you’re ready to create you account and start logging some data, sign-up with the button below.


Blood Type – The Basics

Can you name a famous football player?

What about a Real Housewife?

Now, can you name your blood type?

If you answered “no,” you have a problem. Knowing your blood type can come in handy — to say the least — in a variety of situations.

The Benefits of Knowing Your Blood Type

  1. Emergency preparation:

Not all blood types are compatible when donating or receiving blood. And, blood type is inherited, so that’s why it’s important to determine blood types for the entire family. Knowing which family member you can give or receive blood from during an emergency could mean the difference between life and death. If any family members have a rare blood type, you might even consider banking some of your own blood for emergency situations.

Blood Types

Blood Types

  1. Susceptibility to diseases:

Some blood types are at higher risk for certain diseases. For example, people with the AB blood type have a higher risk of heart disease and people with the O blood type are more prone to retain stress hormones in their system. So knowing your blood type can be a valuable piece of data to help you assess your own risk factors.

  1. Helping others

According to the Red Cross, every two seconds someone in the U.S. needs blood. Two seconds! Donating blood can help save the lives of others. Hospitals are usually low on type O (the most common) as well as O- (the universal donor). If more people knew their blood type in an emergency, hospitals could make better use of their reserves without always having to resort to O- for emergency transfusions.

Compatible Blood Types

Compatible Blood Types

How to determine your blood type:

  1. Ask your doctor during your next visit:

If they don’t have this information on file already, they can order the appropriate test for you.

  1. Do it yourself:

There are numerous options to order your own blood tests online without having to go through a doctor. Here’s one example from Request a Test.

How to update your Heads Up Health profile:

Navigate to the “Profile” section and update your blood type in the top left tile.

Blood type shown in Heads Up Health profile

Blood type shown in Heads Up Health profile

Important: Be sure to also upload a copy of the report from the lab into the “File” section. In many cases, doctors will want to see the actual lab report so they can be certain about your blood type before taking any action.

Add your lab report to your Heads Up Health files

Add your lab report to your Heads Up Health files


Here’s a quick video tutorial that summarizes what we’ve covered here.


If you’re ready to add your blood type to Heads Up Health, head over to our website and get started. Or if you just want the latest from Heads Up Health, follow us on Facebook or Twitter.

Questions? Shoot us an email. We’re here to help!

Eye Exam – The Basics

Eyes are the windows to the soul. Pretty important, right?

Then why is it that an estimated 61 million Americans are at risk for vision loss, and yet only half have visited an eye doctor in the last year?

Eye exams can be easy to forget. Unless you have a problem seeing or need your vision prescription for glasses or contacts, years can go by without getting an exam.

Be empowered to prioritize your eye health. You could see some major benefits of getting an eye exam like:

1. Prevent blindness or decreasing  vision

Despite strides in healthcare and technology, the number of Americans with eye diseases is actually increasing. And the vast majority of cases of blindness are caused by diseases like cataracts, glaucoma and diabetic retinopathy. Less than four percent of cases of blindness are due to injuries. Which means you should be less concerned about shooting an eye out and more concerned about getting an eye exam.

2. Check your overall health

Your eye doctor can tell if you’re developing a chronic disease like high cholesterol, high blood pressure or diabetes just from looking at your eyes. By getting an eye exam, you may get the kick in the butt you need to make healthy lifestyle changes or to make an appointment with your Primary Care Physician to discuss your overall health.  

3. Save money

Because an eye doctor could be your first healthcare provider to detect a chronic disease, treatment for the disease can begin earlier, which usually leads to less complications and could slow the progression or even reverse it. And that saves money for you and your health insurance. If everyone received early detection and treatment of chronic diseases, we’re talking a savings in the billions of dollars.

Chart via

Chart via

How Often Should I Get an Eye Exam?

The frequency of eye exams depends on your age, gender and health risks. For the most part, children and people over 40 need to go more frequently. Adults in their 20s and 30s can space exams slightly further, around five to 10 years. Ask your doctor at your next eye exam how frequently you should be seen.

Eye exam frequency by age

Eye exam frequency by age

How to update your Heads Up Health profile:

Navigate to the “Profile” section and scroll to the tile for “Routine Screenings.” Then add the date of your last eye exam.

Add the date of your last eye exam in your Heads Up Health profile.

Add the date of your last eye exam in your Heads Up Health profile.


Important: Be sure to also upload a copy of your eye exam into the “File” section. If your doctor detects a chronic condition, you’ll probably need to share that report when you seek treatment. This could also come in handy if your vision prescription is documented and you need to order new glasses or contact lenses.


Upload your eye exam report to your Heads Up Health files

Upload your eye exam report to your Heads Up Health files


If you’re ready to add your last eye exam date and record to Heads Up Health, head over to our website and get started. Or if you just want the latest from Heads Up Health, follow us on Facebook or Twitter.


Questions? Shoot us an email. We’re here to help!