I've had the same feedback from a couple of people now. Garmin HR sensors take some time to settle when you start using them, either as a result of needing to warm up a bit (get a bit "moist under the strap", as it were) to improve the contact or because of the static caused by a fresh clean dry technical t-shirt.
We've had our first tastes of cold winter air in the UK over the last few weeks. Cold air has a lower capacity to hold moisture, and when it's cold it'll take longer for your body to warm up and start to perspire. As I explained in my last post, I was making an effort to warm up very slowly in Brighton, and it took 20 minutes (twice as long as I've noticed before) for my heart rate measure to come down. I don't cycle in technical t-shirts and by the time I moved onto the brick run example I gave I'll have already been very well warmed up, and therefore no spike was evident. I run with a Garmin Forerunner 910XT.
So the question becomes - did my heart rate ever go up that high in the first place? I'm starting to think that maybe it didn't.
Firstly, thanks to Louise for showing me her Garmin plot featuring exactly the same thing up to a positively humming-birdesque 220bpm! Follow her parkrun and ultra exploits on twitter and on her blog.
2-hour run from Louise, with a phenomenal spike in the first 5 minutes
Finsbury parkrun, again from Louise, with a similarly extreme first 5 minutes
Secondly, thanks to Rob and Sam for their comments on my last post bringing my attention to the moistness/technical t-shirt behaviour.
Finally, thanks to Robbie C who shared the activity from his easy (for some, maybe!) run round Regent's Park which also shows a starting peak, though not quite as pronounced as Louise's or mine form the weekend. His run was on December 7th which was a cold day, so that might explain why it took longer to read accurately and drop down - 20 minutes, about the same as mine.
Run from Robbie C - I wonder if he knows he ran straight past my office twice? :)
I'm going up to Darlington this weekend to visit my Dad and take in a parkrun (I think we can be fairly sure it'll be cold there) - so I'll make sure I moisten my strap properly in advance and I won't wear a technical t-shirt - I have a very warm Nike base layer I can wear, plus a jumper or something.
I'm planning a hard run, so even if there is a peak it should be narrow as I'll warm up quickly. Let's see what happens...