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?