How to get the most out of your camera measurement in HRV4Training
Practical guidelines and protocols
In this post, I cover best practices and provide some additional guidelines for the camera-based measurement in HRV4Training. In the second part of this post, I provide general guidelines that apply regardless of your measurement setup.
HRV4Training's unique camera-based measurement is scientifically validated and has shown to be equivalent to chest strap measurements as well as electrocardiography (find out more here).
On Android, fragmentation might cause issues. While we cannot test all devices and guarantee accuracy on the different Android phones, cameras, and operating system versions, we developed methods to detect possible issues with your specific setup and inform you, so that you can take action.
Please read below for some additional information regarding measuring with the camera on Android and check out this post for our validation on Android.
Contrary to pretty much all other systems out there, HRV4Training provides a signal quality estimate for each of your measurements, so that you can determine if the data was collected reliably.
Camera guidelines
Make sure to follow these guidelines for all your measurements:
Make sure the flash turns on. If the flash doesn't turn on, the app won't be able to measure with high accuracy (which is the reason why you can't measure using some iPads, unless you use a bluetooth sensor). If the flash doesn't turn on and you have an iPhone, go under your iPhone's settings (in your phone, not in the HRV4Training app) and make sure that HRV4Training is allowed to access your camera. Android apps also need permission to access the camera, you can enable the app from Settings / Apps / HRV4Training, Permissions on Android.
Make sure to cover the back camera completely. In some phones, the flash might be quite far from the camera. Try to cover entirely the camera and also the flash as much as you can, using only one finger. If you cannot cover the flash, that is typically fine, as long as you are close to it with your finger. You can always practice under Menu / Resources / Practice mode.
Make sure there is limited light (apart from the flash) in the room you are taking the measurement in. Measuring in dark places provides better measurement as natural light does not interfere with our algorithms, while we measure blood flow using light reflection.
Place your hand on the camera before tapping the "Measure HRV" button. The app will discard the first few seconds of data regardless, but placing the finger before starting the measurement can still be beneficial during the first few seconds.
Try not to move your finger and not to change the amount of pressure on the camera. Keep your finger still and in a comfortable position. This is the most important point. While we have techniques in place to cope with motion artifacts, movement will most likely mess up your data beyond what can be fixed.
As first-time users, try to take 2-3 measurements following the advice above, and you should be able to acquire high-quality data rather easily. Try to make sure the data quality is labeled as "Optimal" by the app, and repeat the measurement otherwise. If you experience additional issues, feel free to contact us. You can try the camera measurement anytime from Menu / Resources / Camera measurement practice mode.
The app provides the following signal quality categories:
Optimal: PPG was clean and there were either no ectopic beats or issues due to motion artifacts or a very limited amount of noise that could be dealt with by our artifact removal algorithms (for example change of pressure, or slight finger movement).
Good: More issues than in the previous category, motion artifacts most likely dealt with, but we would still recommend taking another measurement if you are not confident in the score (e.g. it is particularly high). Your heart rate data on the other hand is still reliable, and if you use your heart rate data more than your HRV data to guide your training or explore trends, there is no need to take another measurement.
Poor / not good: Major issues in PPG signal quality and artifacts that could not be dealt with without disrupting your HRV. It is highly recommended to take another measurement.
Additional notes for Android measurements
First of all, make sure that HRV4Training is allowed to access your camera. Android apps need permission to access the camera, you can enable the app from Settings / Apps / HRV4Training, Permissions.
As mentioned above, while we cannot test all devices and guarantee accuracy on the different Android phones, cameras and operating system versions, we developed methods to detect possible issues with your specific setup and inform you, so that you can take action.
In particular, during the Practice mode as well as during each measurement, we check that the camera is providing frames at the required frequency and with very limited variations, which is key to providing accurate data. If your phone is unable to sustain the required frequency or lags some frames, we can detect it and inform you, as shown below.
Sometimes terminating other apps or making sure that there are no other time-consuming processes going on in the background can be sufficient to obtain a good reading. You can also try to force-stop HRV4Training and launch it again. However, if the problem keeps showing up at each measurement, it could be that simply your setup does not work with this sensor modality. In this case, we recommend using a Bluetooth SMART sensor, for example, a Polar H7, H9, or H10 chest strap. If you do not plan to use HRV4Training using a chest strap, you can always get a refund on the Google Play Store.
General guidelines (camera or chest strap)
Here are a few other points that are relevant regardless of the sensor modality you use (camera or Bluetooth sensor):
Take the measurement first thing in the morning, possibly while still in bed, or after a bathroom stop, if you need to.
Take the measurement always in the same body position. For endurance athletes or individuals with particularly low resting heart rates, we highly recommend measuring while sitting. Learn why, here.
Relax and breathe freely. It's important that you breathe at a breathing rate you feel comfortable with, do not breathe excessively deep, simply relax and breathe normally to avoid impacting your HRV. Try to be consistent over time (it is easiest than it sounds).
Try not to swallow while measuring. Swallowing is known to induce tachycardia, and therefore disrupt autonomic nervous activity. While typically everything goes back to normal within one breathing cycle or two, a very short HRV measurement will most likely be affected by swallowing, and therefore we suggest re-taking the measurement in this case. See an example here.
Try to relax before measuring. Avoid reading your email and other notifications that might affect your mood acutely before your measurement (i.e. short upsets that might influence your HRV measurement).
Avoid drinking water before a measurement. Water intake increases HRV due to changes in blood volume.
That’s all, thank you for your support, and I hope our tolls will be helpful in capturing useful data in relation to the stressors you face.
Take care
Endurance Coaching
If you are interested in working with me, please learn more here, and fill in the athlete intake form, here.
Marco holds a PhD cum laude in applied machine learning, a M.Sc. cum laude in computer science engineering, and a M.Sc. cum laude in human movement sciences and high-performance coaching.
He has published more than 50 papers and patents at the intersection between physiology, health, technology, and human performance.
He is co-founder of HRV4Training, advisor at Oura, guest lecturer at VU Amsterdam, and editor for IEEE Pervasive Computing Magazine. He loves running.
Social:
Just bought the app! The link above at “See here how to use an iPhone 11 or later” is broken. Maybe it's worth including in the main text, as the iPhone 11 is getting pretty old!
Thanks for your support and information. I use the camera on an iPhone 15 Pro and usually I get an optimal reading but lately at around 37 ses to completion the colour goes orange- without me seemingly moving my finger- Sometimes it will go back to green before the end, but not always. Consequently I are not sure if my measurements are accurate- The message at the end says measure again. I can do this 4-5 times and still not get an optimal result. Any advice? What has changed that I can’t get an optimal result?