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I use a "Polar WearLink heart rate sensor with Bluetooth" while running and my smart phone with Run Keeper to monitor among other things my heart rate. I also use earphones to get information from Run Keeper during running.

Normaly first measurements when starting running are at about 120bpm and ramp up during a couple of minutes to 140-145 only increasing slowly up to 150 or less in the first 20 minutes, depending on training intensity.

But during the last two exercises I was getting a heart rate of 160! This certainly is bogus because it doesn't match at the way I felt.

On the first run where this happened I was wearing a jacket with the cable of the earphones running under the jacket.

On the second occasion I noticed that the cable of my earphones was banging against my chest right where the sensor of the heart rate monitor was.

The weird measurements stopped after I opend the zipper of the jacket / tucking the cable to the side away from my chest.

So my theory is: the beating of the cable against the sensor was somehow picked up as heart beats.

Questions: Is this a reasonable theory? If not, what else might cause this wrong measurement?

If it is a reasonable theory, what could I do to prevent this from happening again, apart from keeping the wire of my chest? A patch on the sensor maybe? Or some "better" earphones? I'd like to avoid fiddling with the cable during running since I find it rather distracting.

UPDATE In another run I saw the same effect: firstly improbable high heart rate, then after some time more reasonable measurements, which I could confirm roughly by manually measuring my pulse. The difference was that my headphones cable was tucked away behind my shoulder, so it doesn't seem to be involved ...

What else could yield this effect?

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  • I'm not sure, but a rest rate of 120 bpm sounds like a medical emergency to me. It better be the cable. – John Dvorak Oct 15 '13 at 7:52
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    what's wrong with 120 bpm shortly after starting an exercise? – Jens Schauder Oct 15 '13 at 7:56
  • misread, sorry. It still appears to be way too high. 150 bpm = 2.5 beats per second. – John Dvorak Oct 15 '13 at 7:59
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    Well known rules of thumb give a maximum aerob heart rate of 150 so getting there after quite some time of exercise sounds fine to me. While 160(well in the anerob) after just starting would indicate a technical or medical problem. Hence the question. – Jens Schauder Oct 15 '13 at 8:03
  • 150 bpm is not high at all for someone running. However, if your polar HR monitor is reading 160, did you take your pulse manually to compare? – JohnP♦ Oct 15 '13 at 15:20
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There can be a couple things going on here:

  • The strap needs to be wet to ensure good measurement of your heart rate. If you start dry, it takes time for sweat to do its job and the early readings can be thrown off because of it.
  • The electrical impulses from the headphone wire can be interfering with the sensors. This is more probable if you listen to music with a steady beat with heavy bass.
  • There can be something interfering with the Bluetooth pairing. This is more probable if the PIN for the Bluetooth device is something that you cannot set, and is shared among all the heart rate monitors. If you run with someone, you might be picking up their heart rate if they are using the same device.

The strap has two sensor areas that align on the chest on either side of the heart. The sensor areas need to be pre-wet, or in cases where there is some interference you might need to get some heart rate monitor gel to ensure a better contact. The strap shouldn't slip as you run.

If you run with someone, make sure you aren't experiencing cross-talk. If you can customize the PIN you use for the Bluetooth device, please do so. That will help minimize the chance that you are picking up someone else's device.

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Don't discount outside interference. I wear a Polar heart rate monitor and it sometimes has problems when someone with an electronic device comes close to it. It's anecdotal evidence, but, when dealing with devices that are not hard wired, I think it's plausible.

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