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, armbands, 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 wristwatches, 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 and allow 3rd party apps like ours to pick them up (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. For those watches with a built in HRV function, if you'd like to try measuring HRV with them, you'd need to do a manual measurement, holding your arm and wrist as still as possible.
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 with the Elite HRV app, as Apple now advertises that the watch is capable of measuring HRV. In order to calculate the research-backed HRV values such as RMSSD, LnRMSSD, HF, LF, etc. our software needs access to accurate R-R interval data. (More info on R-R intervals here).
At the time of this writing, the Apple Watch has only recently started to transmit R-R intervals to 3rd party applications such as Elite HRV. Since accuracy is our priority, we need to do in-house testing of the accuracy of these R-R intervals before making the developmental changes needed to connect the Apple watch to Elite HRV.
Regarding the HRV function provided directly by the Apple watch: 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. If you would like to test out the Apple Watch HRV function, we recommend triggering manual HRV reading and sitting as still as possible. This data will not be pulled into Elite HRV, so you'll need to view it on your Apple Health app.
To be sure, if you are moving your hand, wrist or arm at all, then there is a very low degree of confidence in the accuracy of the HRV calculations that could be produced from the Apple Watch at this time. Even if perfectly still, there are many circumstantial variables to address such as sensor positioning, skin contact, skin thickness/color, emitter spectrum, etc. We will need to verify the accuracy of the raw R-R intervals before updating our app and Compatible Devices list.
There are many heart rate monitors that are compatible with Elite HRV and fulfill the above requirements. For a full list, see: Compatible Devices (link)
We will update this article and our Compatible Devices page accordingly when the time comes.