Yesterday at the Leadville Trail Marathon, my Garman 920XT indicated I had a heart rate spike while climbing and descending the main peak, which tops out at 13,300 feet. Graph here: https://www.strava.com/activities/1041780092. Basically, I'd been keeping my heart rate steady around 140 the whole morning. At about 12,700 feet, my watch indicated a heart rate spike at first to 170-180, then over 200. I didn't feel terribly different, but I was concerned enough to ask a buddy running with me to give me a 15-second count while I counted my heart beats. My manual check suggested around 130bpm, so I kept heading up the mountain. The watch indicated about 180 while I was atop the mountain for a few minutes, then went back up to over 200bpm as I started down. When I got below 12,600, it all went back to normal, around 130-140bpm.
1. Anyone know of HRM watch-related issues at altitude? My buddy also had a similar spike, but shorter and not as dramatic. Basically same place, same time. Watch issues or similar physiological responses?
2. The brief elevated rate was approximately 150% of what I'd expect. I do have an otherwise harmless arrhythmia. Any chance a HRM would particularly pick that up only over a certain altitude and is that what it would look like?
3. The wind was howling at the top, could clothing slapping against a HRM make it malfunction like that? Obviously there could be other external signals interfering as well, but the seeming altitude-dependent nature of the spike seems peculiar.
Thanks for any thoughts!