Why Watches and Wrist HR Monitors Usually Don't Work For HRV
Elite HRV works with any sensor or device that transmits accurate R-R intervals via Bluetooth 4.0+ protocol.
Different devices are designed for different purposes. Most watches, arm bands, and fitness heart rate trackers are designed for heart rate only. This means that they do not accurately measure R-R intervals. R-R intervals are the exact time measurement in milliseconds between each heartbeat that are needed for truly accurate Heart Rate Variability (HRV) calculations. These millisecond times between each beat are also called IBIs or inter-beat intervals.
Due to the limitations of those hardware devices, we generally do not recommend them for reliable HRV readings. These devices are fine for just getting your basic heart rate though! Many devices claim to be "ECG accurate", but they are not specifying for what parameters. Most of the time accuracy claims are referring to heart rate (beats per minute, BPM) or a non-HRV measure, such as detection of atrial fibrillation, which has different requirements than HRV calculations.
Examples of devices that do not measure HRV include: the Fitbit Charge HR, Mio wrist devices, Polar wrist watches, etc. Here is an example of a study showing the limitations. We hope the hardware will advance sometime soon and provide accurate R-R intervals (We know they are very convenient!).
There is no affordable hardware or sensor on the market that can measure accurate HRV from the wrist, arm, or hand using optical sensors or PPG while you are moving. You must remain still (within reason) to accurately measure HRV using that technology in those locations on the body.
In the meantime, the best option is to invest in a chest strap heart rate monitor or an HRV-specific device like the CorSense. These devices are built for accuracy first and specifically for Heart Rate Variability.
Some devices with a "closed system" claim to measure HRV, but access to the data is not allowed, so we cannot comment on the reliability of these systems. In order to calculate HRV values, we must receive the R-R interval data or full access to the raw sensor data.
For the Garmin Vivosmart 3 specifically, Garmin Customer Service reports that the sensor is not intended for HRV analysis by users or by 3rd party apps (more info provided by Garmin here).
For a list of heart rate monitors that are accurate enough for Heart Rate Variability measurements and give you full control over your data, see this page: https://elitehrv.com/compatible-devices
More about R-R intervals or inter-beat intervals (IBIs): What are RR intervals?
Scosche Rhythm 24
We realize that new devices are coming onto the market that are supposed to transmit accurate R-R intervals. While this may very well be the case, we cannot recommend or officially support these devices until we have time to do our own internal testing. You can check our Compatible Devices page for updates!
We have had many recent inquiries about using the Apple Watch 4 with the Elite HRV app, as Apple now advertises that the watch is capable of measuring HRV. We still cannot support this device for the following reasons:
- The Watch still does not transmit accurate R-R intervals to 3rd party apps, meaning even if the watch is transmitting accurate data, it will not transmit it to our app or any other 3rd party app; the data is only available to the Apple Health app. A 3rd party app cannot trigger an HRV measurement (such as our app triggering a Morning Readiness reading - it is not yet possible). The watch does NOT share the ECG data.
- The data that is computed by the watch and Apple Health app is the SDNN value, where as our app uses the rMSSD value to compute our HRV score. This is because we believe that while the SDNN value is used medically for longer measurements, the rMSSD value is more accurate for shorter measurements.
- The Apple Health app pulls HRV data at random times throughout the day. This offers little to no context for the HRV score, and therefore can be very misleading when trying to make a judgement from that score. The point of our Morning Readiness readings is to establish a baseline, so to take readings throughout the day without this baseline will not tell you much.
There is always the possibility that Apple will expand the watch's capability and accessibility. We will update this article and our Compatible Devices page accordingly when the time comes.