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:
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:
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:
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:
Physical stress such as high-intensity exercise
Mental and emotional stress
Over-training / injury
Sleep quality and quantity
Drastic changes to daily routines
Blood sugar fluctuations
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!
Flatt, A.A. Improving HRV Data Interpretation with the Coefficient of Variation https://elitehrv.com/improving-hrv-data-interpretation-coefficient-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.
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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.
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The Carb Tolerance Test is a powerful tool from Heads Up Health that anyone can use to optimize their health. By helping you test and identify foods that are optimal for your own body’s blood sugar levels, the Carb Tolerance Test can help you fine tune and customize your diet for optimal blood sugar control. (more…)
In this post we will examine the “glucose ketone index” as a biomarker for tracking metabolic health. We will also explore some of the primary use cases for tracking the glucose ketone index including cancer treatment, weight loss, metabolic disease management and athletic performance. Lastly, we will demonstrate how you can use Heads Up Health to track the glucose ketone index along with all of your other important health data.
If you want to skip ahead, click the button below to create an account with Heads Up and start tracking the glucose-ketone index alongside all of your other health metrics. Or, read on for more information on tracking the glucose ketone index.
The glucose ketone index is simply a way to measure the relationship between your ketone levels and your glucose levels at any moment in time. It is measured by dividing your blood glucose level (mmol/L) by your blood ketone level (mmol/L). The result is a single number we can use an indicator of one’s metabolic state.
The index has its roots in brain cancer treatment, where researchers using metabolic therapy found best results when glucose and ketones maintained a very precise relationship in the patient . Since there are many aspects of daily life (stress, exercise, nutrition etc.) that can upset glucose or ketone levels in the body, thereby throwing off the optimal glucose-ketone ratio, the index was developed to ensure both metrics (glucose and ketones) are maintaining the ideal ratio for optimal treatment outcomes.
Example: If my fasting blood sugar first thing in the morning is 4.6 mmol/L (82 mg/dL) and my ketone reading is 0.8 mmol/L, I would record a glucose ketone index of 5.75 (4.6 / 0.8).
Despite its roots in cancer treatment, the index can also be very helpful for those using metabolic therapy to treat (and prevent) diabetes, obesity, cancer (particularly cancers that express aerobic fermentation) and other metabolic conditions. By using an index that tracks glucose and ketones TOGETHER, we can develop zones that are optimal for addressing various health conditions.
The table below outlines some generally accepted zones of treatment using the glucose ketone index:
Degree of ketosis
Degree of dysfunction
Type 2 Diabetes
Table 1: Optimal zones for the glucose ketone index 
Use cases for tracking the glucose ketone index
1. Cancer treatment
For those using metabolic therapy as a means to fight cancer (e.g. brain and other cancers that express aerobic fermentation), the index is an excellent way to ensure you are staying in the optimal zone .
Maintaining a healthy glucose ketone index (i.e. low to moderate ketosis) may be an effective tool for preventing many common metabolic diseases such as type 2 diabetes. Additionally, it may actually be very beneficial to periodically (once or twice per year) employ a metabolic therapy (such as an extended fasting period) that pushes our index into the 1.0-3.0 range as an effective technique for disease prevention.
3. Athletic performance
By measuring the glucose ketone index and correlating with diet, training regimen and performance, athletes may be able to identify their own personal zones of optimal performance.
4. Weight loss
For those using metabolic therapy to lose weight, the glucose ketone index may actually be a more effective marker than tracking glucose and ketones independently. Heads Up Health can help to track and correlate the index along with other metrics such as weight and body fat.
Tracking the glucose ketone index can be a very helpful piece of biofeedback to understand how your metabolism is responding during the fasting period. Over time, you can look back at different fasting periods and use the index as an indicator of your metabolic state during the course of the fasting period.
6. Feeling awesome
If you are employing fasting and/or ketogenic diets for optimal health, the glucose ketone index can help you find your ideal sweet spot. If you reach a point where you start feeling absolutely awesome (which you inevitably will in ketosis), take a glucose and ketone reading and calculate your index. Having data to know when you are feeling your best will increase your chances of being able to consistently reproduce this state of optimal performance.
Tracking the Glucose Ketone Index in Heads Up Health
In order to track the glucose ketone index, you will need to measure glucose and ketones at the same time. This means two drops of blood – one for glucose and one for ketones.
Create a new Glucose Ketone Index reading by entering both numbers into your Heads Up profile. For those who measure blood glucose in mg/dL, Heads Up Health will convert this number into mmol/L as part of the calculation.
Track the glucose ketone index in your Heads Up Health profile
Once you have stored your first readings, you can track the index on your dashboard along with all of your other health metrics:
Tracking the glucose index on your Heads Up dashboard
Lastly, you can trend the index on the Analyzer and compare it to your other health metrics:
Trend your glucose ketone index over time and compare it to other health metrics.
The following video shows exactly how to enter and track the index in your Heads Up profile:
If you are already tracking glucose and/or ketones or leveraging metabolic therapies such as fasting and ketogenic diets, the index can be helpful metric to track your progress. Heads Up Health can help you track this marker and compare it to your other health metrics. You can create your free account and start tracking this index today.
For those who are looking to reap the benefits of a ketogenic diet, tracking breath ketone levels can be a very helpful part of the process. Breath ketones are a real-time indicator of your level of ketosis which is a big advantage compared to other testing methods that merely indicates traces of ketosis.
New devices on the market, such as the Ketonix make testing easy, affordable and pain free by testing the level of ketones in your breath. At Heads Up Health, we make it easy to record your breath ketones along with all of your other health data. If you are ready to start logging breath ketones now, create your free account using the link below. Or read on to learn more about tracking breath ketones with Heads Up Health.
The first step is purchasing a breath ketone testing device. These devices offer an affordable and reliable alternative to blood and urine based ketone testing. Heads Up Health recommends the Ketonix breath ketone meter. You can learn more about this product by clicking on the link below.
Step 2: Connect Ketonix to your Heads Up account
You can now electronically connect your Ketonix account to Heads Up Health to enable automatic data synchronization. See the video below for instructions and how to use Ketonix and Heads Up together:
Step 3: Customize breath ketones on your Dashboard
The Heads Up dashboard is completely customizable, so you can move the breath ketones card anywhere you want. For example, in the image below, I have my dashboard configured to display breath ketones in the top row, right next to my weight and blood glucose readings:
Configure location of the breath ketones widget on your Heads Up dashboard
Step 4: Explore trends and correlations on the Analyzer
You can use the Analyzer to track your breath ketone readings over time. You can also use the Analyzer to look for correlations between breath ketones and other data sources such as your weight, blood glucose or cholesterol levels:
Examining breath ketones over time and comparing to other data sources
Step 5: Hybrid strategy – tracking breath and blood ketones
Another option is to leverage the reusable breath ketone meter for frequent testing throughout the day/week with less frequent blood ketone readings as needed. This allows you to save money on the expensive blood test strips yet still obtain regular readings with the breath meter. Heads Up allows you to track both separately:
Tracking breath and blood ketones together for a hybrid strategy
You can also compare both readings on the Analyzer to see how breath ketones correlate with blood ketones:
Comparing breath and blood ketone readings
Voila! If you are ready to get started, click below to create your account and start logging breath ketones today. Feel free to send us any comments or questions, we are here to help!