We recently put together a series of posts that cover many aspects of HRV measurement, data interpretation as well as plenty of examples that you can look at to better understand how to make use of the data, and how HRV relates to training and lifestyle stressors.
Check this page for an overview of HRV4Training's main features. Then browse the list of FAQ in this page. Each question points to comprehensive blog posts where we discuss each topic in greater detail
HRV is a term that refers to ways to summarize in a number the variability between heartbeats. Why is this variability between heartbeats important?
For a simple reason: HRV is the only practical, non-invasive and cost-effective way we have to measure the activity of the autonomic nervous system in response to stress
Our body is continuously re-adjusting to maintain a state of balance, called homeostasis. Our heart rate, blood pressure, glucose level, hormones, etc. — react to the challenges we face and the autonomic nervous system works to keep everything in balance so that we can function optimally (e.g. do not develop chronic conditions, or improve our performance)
Heart rhythm (and therefore HRV) is regulated by the parasympathetic branch of the autonomic nervous system, the one in charge of rest and relaxation. Hence, measuring HRV is an effective way to capture how our body is doing while trying to maintain a state of balance in response to different stressors (training, lifestyle, etc.). In particular, a reduction in certain HRV features (for example rMSSD, more on this later) typically means that parasympathetic activity is reduced, and therefore we have not fully recovered or in general, there is more stress in our lives
What does the HRV number represent?
HRV is determined by computing so-called features, starting from a series of RR intervals, or differences between heartbeats. This means that on the contrary of heart rate, which can be thought of as an almost instantaneous value, HRV requires a certain amount of data to be accumulated, before it can be computed
In terms of features, the scientific community settled on rMSSD as the most meaningful and practical feature to use in applied research and real life
Why rMSSD? Because of how our physiology works. In particular, the vagus nerve (representative of the parasympathetic system) acts on receptors signaling nodes to modulate pulse very quickly, on a beat to beat basis. Thus, rMSSD captures parasympathetic activity
How is HRV computed in HRV4Training?
HRV4Training reports HRV as a transformation of rMSSD
In particular, this is the HRV number you see in the homescreen, and is computed as a logarithmic transformation of rMSSD as typically reported in the scientific literature
If you prefer to look at the actual rMSSD value in the app, you can do so by selecting rMSSD View under Menu / Settings. Note that the trends and day to day changes will be exactly the same, as the reported HRV is simply a more user friendly transformation of your rMSSD
Combining your HRV with subjective and training data, HRV4Training will be able to provide you with daily advice and interpret long term physiological trends, as explained below
What can HRV4Training offer beyond daily measurements?
HRV4Training provides data analytics that let you explore:
Weekly and monthly summaries: pick the metric most representative of your athlete's trainings (e.g. RPE, TSS, Suffer Score, training distance) and analyze training load breakdowns by week and month to keep better track of overall progress
Acute HRV changes in response to training and other stressors: systematic analysis of day to day changes in HRV on days following training, alcohol intake, travel, menstruation and sick days. Are your athletes physiologically rested after rest days and easy training? What drop in HRV can you expect after an intense training? How does travel affect their physiology?
HRV trends: provide more insights on the big picture. Look at baseline changes on multiple parameters relevant to your physical condition (e.g. HRV, HRV, coefficient of variation, training load), etc. The app can automatically determine if your recent HR orHRV trend is changing in a trivial way, or if the change is something to take more seriously, based on your historical data
Correlations: mainly for exploratory analysis inside the app. Look at what factors are related to physiological changes, and try to adjust your lifestyle accordingly (a good one is typically sleep quality)
Training load analysis: you can pick the metric most representative of your trainings (e.g. TSS, Suffer Score, training distance or your own custom metric) and analyze fitness & fatigue, determined as chronic and acute training loads, as well as readiness to perform and injury risk
VO2max estimation: for runners and cyclists using the Strava integration and training with a HR monitor (and power), HRV4Training can estimate cardiorespiratory fitness level (VO2max). Check out this post for more details and our publication showing a strong agreement between real life running performance and estimated VO2max
Training polarization analysis: This analysis allows you to get an overview of how hard you are training and potentially polarize more your training, as a more polarized approach, typically involving training about 80% of the time at very low intensities, has been shown to improve performance for both recreational and elite athletes. More details on this analysis at this link
Lactate threshold estimation: Improve your training pacing and racing strategies based on your estimated lactate threshold. Check out this post for an overview of the science behind our estimate and how you can use it
Check out the quickstart page for an overview of these features
What do I get more using HRV4Training Pro?
HRV4Training Pro is the ultimate platform to help you analyze and interpret your physiological data. You can learn more here and find a guide here
In particular, we highly recommend relying in the Overview page in Pro, to look at the big picture. In this visualization you can easily determine when HRV is below normal values (a good time to hold back) while keeping an eye on training load and subjective metrics as well. Learn more about the Overview page, here
We have put together a list of case studies and examples at this link. You'll see the effect of various stressors (training, travel, getting sick, etc.) on HRV and how HRV4Training Pro helps you interpreting the data, so that adjustments can be implemented
How do I use HRV in teams settings?
HRV is about individual adaptations to training and lifestyle stressors. Knowing how each individual responds you can make meaningful adjustments to their training program so that adaptations are optimized and performance improved
We put together an overview of the recent research showcasing what data to look at in the context of training, adaptation and performance, that you can find here. The blog post covers everything from measurement protocol to data analysis, and we highly recommend reading it
In Pro, you will be able to analyze easily and effectively significant changes in HRV (when data goes outside normal values for an individual) as well as the coefficient of variation for your clients and athletes, so that you can make more informed decisions. Learn more about the Overview page, here
What devices are supported?
For the camera version you will need an iPhone 5 or later (all versions). If you use a bluetooth low energy sensor, any device will work, from iPads to iPods. Just make sure you use a sensor that is reliable, for example a Polar H7 or H10
On Android, most phones released in the past few years should work fine,The app is able to detect if your phone is supported, and inform you. heck this post for more details on the camera measurement on Android and this post for a validation with respect to chest straps
We have also released support for the dedicated sensor present in Samsung Galaxy phones, you can choose to use that sensing modality from Menu / Settings
What sensor should I use?
You can rely on the validated camera-based measurement or use a chest strap, in this case we recommend a Polar H7 (that we have also validated) or H10. A validation paper of our camera based algorithms can be found at this link. Other valid alternatives that can be used with HRV4Training are the Scosche rhythm24, the Corsense, an Apple Watch or the Oura ring
What about the Apple Watch?
HRV4Training can now be used to read HRV data and RR intervals from the Health app. Due to some limitations in the way apps can communicate with the Apple Watch, you need to follow the following steps in order to gather meaningful data:
Select Health as data source under Menu / Settings, then authorize HRV4Training to read HRV data from Health, when automatically prompted
When you wake up, take a measurement using the Breathe app on your Apple Watch
Right after, open the HRV4Training app on your phone, tap 'Read from Health' from the main screen, and that's it. We'll be doing the math and prompting you with the usual Tags to fill in, so that you can add context around your measurements
We have also released a Manual Input mode where you can enter your night data from any device, and still get a proper interpretation of your resting physiology in HRV4Training. Learn more about manual input, here
How accurate is the camera version?
The camera version is as accurate as a Polar H7 or a full ECG, as shown in this post and recently published in this paper. Check out also the post below where we show a comparison of peaks detected from a full ECG (Cosmed, reference system) and PPG data acquired using HRV4Training:
Most importantly, check out the next FAQ for tips on how to use the camera properly, since it does take a few measurements to get familiar with it. You can also practice any time from Menu / Resources / Camera measurement practice mode
What's the best way to use the camera measurement?
See this post for a series of tips on how to make the most out of your camera measurement
When should i take the HRV measurement?
Ideally in the morning, right after waking up, so that you can limit the effect of other stressors, similarly to what we would do in laboratory protocols & clinical studies
How should I breathe?
Relax and breathe at your natural pace. Self-pacing seems to be ideal, as each person might have a preferred way of breathing. The important point is not to force your breathing or make any effort to try to breathe particularly deep or in an unnatural way. Simply relax and self-pace your breathing
No, at the moment you can measure only once per day. Making HRV measurement a morning routine, and being consistent (see this post) are key factors to make sure your data can be used to perform meaningful analysis. This being said, if you are a HRV4Training user and would like to experiment more, we are happy to send you a promo code for Camera HRV (also available on Android), so that you can download it for free. Just email us at this email address, specifying your current HRV4Training registered email
How long should the measurement last?
Short answer: 60 seconds are sufficient for a reliable measurement of rMSSD and therefore of HRV4T Recovery points Long answer: read this post in which I analyzed HRV measurements from 10 seconds to 5 minutes, to determine the reliability of different time windows
Can I use HRV4Training for Biofeedback?
We have developed a separate app for biofeedback. Please see this post to learn more about biofeedback, what is the difference from a morning measurement of resting physiology and biofeedback and how you can use the HRV4Biofeedback app
What is the daily advice and how is it computed? What can it tell me?
The daily advice combines your HRV with respect to your normal values, your subjective scores and your recent trends to provide daily guidance. You can find out more at this blog post
Why is my heart rate fluctuating so much during a measurement?
In HRV4Training what we measure are beat to beat differences (also called RR intervals), and what we show is instantaneous heart rate. RR intervals cover a broad range during a breathing cycle, you might also have noticed that while breathing out the instantaneous HR lowers, while it raises while breathing in. You might be surprised by the big range of values covered while measuring using HRV4Training because normally most devices measuring HR through an app, show you averaged data, such as HR averaged over the past 15 or 30 seconds. By definition, your average heart rate over the past 15 or 30 seconds is much less jumpy
As we measure HRV variability, we prefer to provide instantaneous heart rate as visual feedback instead of averaged heart rate. Check out the data below for an example. As you can see RR intervals go from 1000 to almost 1800ms. Heart rate is the inverse of the RR interval over a minute, so we can derive instantaneous heart rate as 60000/1000 = 60 bpm and 60000/1800 = 33 bpm. This is an extreme case of high HRV, showing a variation of almost 30 beats over a breathing cycle. If we were to take the past 15-30 seconds and show average heart rate, you'd probably see something in the range of 40-50 bpm, as other devices would report it
Note also that when using a chest strap the same relation holds. The standard bluetooth low energy protocol provides data in a packet which starts with your average heart rate, and then appends all RR intervals detected in the past second (zero or more). Most apps would take the heart rate sent by the polar and display it, thus showing you averaged information. On the other hand, HRV4Training takes the last RR interval received and computes your instantaneous heart rate as shown above, to provide you with real-time feedback on beat to beat variability
Should I do single or orthostatic measurements?
Short answer: single HRV measurements are sufficient to monitor day to day training load and recovery Long answer: read this post in which I analyzed data from HRV4Training users, showing that single measurements, either lying or standing, provide accurate assessment of training load, while "traditional" orthostatic measurements do not seem to provide additional help in guiding day to day training.
What are population values for HRV?
HRV population values cover a very broad range and tend to lower with age. While some parameters like age and fitness influence your HRV, your baseline is also affected by other factors more difficult to measure, such as genetics. For a more detailed discussion on population values, check out this blog post
In the context of HRV analysis, we always stress the importance of looking at your own relative changes over time. Our baseline HRV is probably affected by some factors that we cannot easily measure (genetics, for example, as reported once again recently), other factors that change but we have no control on (e.g. age), and factors we can probably influence (lifestyle)
Hence, we highly recommend to focus only on relative changes, which is the most powerful way to make sense of your data
Can a high score be bad?
Normally a higher score indicates relatively lower stress, however we take sometimes a more statistical approach in which we interpret everything that is "not normal" (particularly low or high), with respect to your historical data, as something to be more cautious about, especially if subjective scores (sleep, motivation, perceived performance) are not trending well
Keep in mind that these are uncommon situations and normally we would consider a higher score positively, and a lower one negatively, as that's how higher stress level is reflected at the physiological level. At this link you can find more information specifically on how we build the daily advice
Is HRV4Training performing any correction for ectopic beats and motion artifacts?
Short answer: yes, HRV4Training performs RR interval correction to deal with ectopic beats and motion artifacts Long answer: see this blog post to find out more about RR interval correction, ectopic beats, motion artifacts and how we deal with these issues in ECG, Polar and PPG data
I measured twice in a row and my measurements were different. What does it mean?
Daily measurements taken in succession can vary, and variations of 5 - 20 ms or 0.5 recovery points are perfectly normal, simply because our physiology is never in the same state. Thus, HRV4Training uses your historical data, as much as the past 2 months of data, to understand what are normal variations for you and provide meaningful daily advice regardless of these variations
For a broader discussion of this topic and some data from our clinical studies showing the effect of measurement duration and paced breathing on measurement repeatability, check out this blog post
Can I record more than one workout per day?
We currently support multisport activities (manually or automatically read from Strava) for triathlon combinations as well as other workouts supported in the Strava and Training Peaks integration. We also support custom tags (or annotations) so that you can code up to three different parameters that are particuarly relevant to your lifestyle or training. Each numerical custom parameter could be coded to log additional workouts, for example as 1/0
An additional note which is important in the context of interpreting data: note that what matters here is the overall stress you put on our body, and the different stressors cannot be separated, so when we measure in the morning, we measure the overall stress which comes from all our trainings, and not only training as a matter of fact (for example stress coming from other aspects of our life). This is also the reason why there are metrics that try to capture overall load independently of the sport, and that can include already both intensity and duration, for example TSS. It's more important to try to capture overall load this way, maybe with a metric that works well for you, than to have a complete list of sports and activities. RPE could also be used as a overall RPE of our day, which will reflect in our physiological stress level. In this way, we can explore the relation between load and physiological responses meaningfully
How do I use HRV to adjust or guide training?
Let’s revise the basics: HRV, issimply a way to capture parasympathetic activity, or in other words, level of physiological stress. As we apply stress to trigger certain adaptations, measuring our body’s response to such stressors, as well as to all other forms of stress we are affected from (e.g. simply life happening, work stress, family, etc.), is very helpful as it can provide objective feedback and help us making meaningful adjustments
The simpler adjustments is probably just being a little more honest with ourselves, and slowing down from time to time, especially when our body is already too stressed. The example we’ve just highlighted is something we all understand quite well, higher stress as shown by lower HRV highlights how it might be a good idea to take it easy and avoid excessive stress which might lead to overtraining or slower recoveries, hindering improvements in performance
When everything is within your normal values or in other words a green light, should give you confidence that everything is going well and in general you are coping well with your current training and lifestyle. Yet, if your training plan says you are due for a rest day, take it. If you are due for a low intensity workout, do it. It is important to understand that HRV and physiological measurements are tools for awareness, which allow you to understand how you respond to a particular plan, not to replace your plan entirely
You can learn more about medium and long term trends, at this link
Can HRV4Training share data with other apps & services?
When authorized, HRV4Training can share data with the following apps and services:
Strava: HRV4Training can read your workouts summaries, show them in your History page and fill in automatically some of the training-related tags for you, as explained here. Strava data is also used to estimate VO2max for runners and cyclists using a heart rate monitor (and power) during training
TrainingPeaks: HRV4Training can send HR, HRV and additional parameters (notes, sleep, muscle soreness, etc. ) to TrainingPeaks, as explained here
Apple Watch: you can measure HRV using the Breathe app, which writes to Health. HRV4Training can then read from Health your data, as explained here
Oura ring: we can read night data from Oura cloud so that you do not need to take the morning measurement. Learn more here
SportTracks: HRV4Training can send HR and HRV data to SportTracks, as explained here
Genetrainer: HRV4Training can send HR and HRV data to Genetrainer, as explained here
Health: HRV4Training can send HR and sleep data to the Health app as well as read sleep data from the Health app in case you use another sleep tracker
Today's Plan: HRV4Training can send HR and HRV data to Today's Plan. Learn more about this integration here
Final Surge: HRV4Training can send HR and HRV data to Final Surge. Learn more about this integration here
TrainAsOne: HRV4Training can send HR and HRV data to TrainAsOne. Learn more about this integration here
Oura ring: HRV4Training can read HR, HRV and sleep data from Oura. Learn more about this integration here