Heart Rate Spikes and Dropouts With the Polar H7 and Other Heart Rate Monitors

See Also: Troubleshooting BLE Sensors

Have you been having spikes and dropouts in your heart rate monitoring? Especially with chest straps, such as Orange Theory and Polar H7, H10 or other devices.

If you are using the Apple Watch and experiencing flatlines, please see the article on Optimizing Apple Watch.

The way the belt works is that it receives electrical signals from the heart that are then shown as Beats Per Minute. However, without some kind of moisture (such as saliva, water, or a conductive gel) to act as a conductor between the heart and the belt, the signal will not be strong or consistent. We believed this is what causes erratic data, so we threw our lab coats on and decided to run an experiment.

Dropouts, which often are represented by “Flat Line” readings on the chart, are very typically low battery level or lost connection issues. An interesting note however; with certain devices such as the Polar H7 which have dual mode operation, the same heart rate monitor can read just fine on gym equipment while struggling to keep connection with the app. This is because the channel the H7 communicates with the gym equipment requires less battery power, so a low battery can be enough to power that channel (5.8 GHz) than BLE. Check out this great article on changing your Polar H7 battery.

Note: The Fitdigits app does not manipulate the data it receives from a heart rate monitor at all.

Immediate spike caused by conductivity issues

The Experiment: We decided to go out for a run using two devices, the Fitdigits app as well as a Polar watch. We connected both with the Polar H7. The interesting thing about this experiment is that the phone and the watch use two different platforms. The iPhone uses Bluetooth Smart to connect with the H7, while the watch uses a 5.8 kHz signal to pair. This enables us to be comfortable concluding that if both devices spike, it is because of the belt and not because of an issue with the app, or a specific platform (such as Bluetooth Smart). So basically we went out for a run with both devices, and whenever we saw a spike in the Fitdigits app, we compared those results with the Polar watch.

The Results:The run started with a bang, spiking right off the bat and soaring to unforeseen heights all the way out of zone 5! The watch mirrored the results. When the heart chart on Fitdigits showed our BPM going above zone 5, the watch showed exactly the same results, with no discernible difference.

Conclusion We conclude that the spikes are a result of conductivity issues and / or hardware issues, not the app itself. Any time you get a spike or dropout, it is either the result of your body not having enough moisture to get a firm connection with the belt, or, in more rare cases, the hardware going bad, many times the belt, but less frequently the HRM “peanut” (brain) – the part that clips into the belt, goes bad.

We also believe messing with heart rate numbers received from a device is not a good policy, even if it is due to these malfunctions.


If you get spikes at the beginning of your activity, typically that points to a connection issue between the strap and your body, since you haven’t yet really begun to sweat. We strongly suggest wetting the strap with either water, saliva, or a conductive gel. Fitdigits has a great blog post on Troubleshooting Your Polar H7, and noted fitness blogger DC Rainmaker also has a great post on How to Fix Heart Rate Strap Dropouts/Spikes.

If you are mostly walking / running / biking, you might consider getting and Optical HRM (like the Scosche Rhythm+ or a Mio HRM) instead of the Polar (or any chest strap). Typically, not being electrical per se, they have less of these issues.


If you still are experiencing issues, please contact Fitdigits customer support.

10 thoughts on “Heart Rate Spikes and Dropouts With the Polar H7 and Other Heart Rate Monitors”

  1. I experience this quite regularly with my Polar H7, surely it would make sense for Digifit to add the ability to filter the data spikes and have this as a user option.

  2. Surely you jest. I get spikes using my Polar Old Skool Bluetooth belt with Digifit but not with other apps. The spikes are always the same, a reading of exactly 209 for a sample or two or three, and then back to normal.

    Now a reasonable person with knowledge of human anatomy would readily surmise that my heart rate did not really jump from 140 to 209 for a second and then go back to 140, so it's clearly a false reading, and it may very well be Polar's fault.

    However, the fact remains that neither Polar nor the user has the ability to ensure that every reading is correct; the one I got today was not caused by a dry strap and was not at the beginning of the workout. So only the apps maker as the power to throw these bogus readings away and replace them with an interpolated value.

    You need to do what *every other application* that has recorded raw sensor data has done from the beginning of time: smooth the data, filter the noise, don't be an idiot. This is so elementary to real time data collection it should not be necessary to explain it.

    If you collect 5000 samples ranging from x to y, and 4995 vary by no more than 5, a variation of 60 or more in the remaining 5 is an indication of bad reading. People are not using their straps in a lab setting, after all.

    I hope this is clear.

  3. I had to laugh on this one! I started getting dropouts and then discovered I had lost so much weight that the belt was too loose!!! Great problem to have and an easy fix.

  4. I've found it easy to eliminate this problem by making sure the strap is not only moistened, but also on TIGHTLY! Many people I know with this strap have not tightened it enough which is why they have peaks and valleys everywhere – similarly with swimming. I can now swim with my H7 no problem, but it has to be tight enough that the flow of water over me doesn't pull the strap away at all. It was uncomfortable at first, but I guess I've gotten used to it over time.

  5. An important note from a user:

    If anyone is experiencing spikes and drop outs it is my suggestion that they check with their doctor to see if they have Atrial Fibrillation. I do and I am taking medication for it. When I am working out with my Polar H7 it picks it up and yes, it can occur in one or two seconds from a very low to a very high (over 200) or in the opposite from high to very low. If AFIB goes undetected and untreated there is a strong possibility that someone’s exercise routine will come to a terminal stop.

    So while it may be the device or strap, it could be your heart trying to tell you something is not right. If anyone is serious about keeping fit, does it not make sense to make sure your main body organ is working properly?

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