Monday, October 1, 2012

Heart rate spikes and my HR monitor

Mystery spikes at the beginning of my runs
I started using my heart rate monitor again in late August and it's helped me understand how much (or how little) work I'm putting into a run. Instead of looking at my Garmin and checking my pace for that moment, I now display my heart rate and adjust my effort depending on what I see. I've learned that my default pace happens when I'm running in the zone 2 range, far below what I would have thought.

Now, when I see that my heart rate is still in the "easy" zone, I'll pick up the pace to cross the threshold to the next level. I aim to reach zone 5 by the time I finish most of my runs and I usually get there.

I was looking at the readings from yesterday's run and noticed that my heart rate was holding close to 100% of Max through the first three minutes. From there it dropped precipitously down to 76% for no apparent reason. I had seen this happen before, my first few minutes of the Cow Harbor 10K show a spike to 100% of Max before dropping to 80% at the five minute point.

In the case of Cow Harbor, I was pumped up for the race and had consumed a 2nd Surge gel with caffeine right before the start. In contrast, yesterday's run was low key, with no gels or caffeine to influence my physiology. In both cases I felt no different between the high and normal readings. Since it doesn't correlate to my condition, I'm thinking the reason is completely benign.

In both cases the humidity was low and I had not wet the HRM sensor before I linked it to the Garmin. Without moisture from sweat, the readings were probably unreliable. After a few minutes of running (and sweating) they dropped to an expected level. I'll test this theory tomorrow by ensuring the contacts on the HRM are wet before I start my run. I'm pretty sure I'll see a smoother curve along the timeline.


  1. I often wear the heart rate monitor for my Garmin Forerunner 305 and have found the readings to be way to high in the beginning. It sometimes indicates a rate above 180 and I know that can't be true based on my pace and effort. After about a quarter mile the readings normalize.

  2. Hi Paul - I'm glad to hear you say that because it confirms my experience as well. I also saw some stuff online that corelated artificially high readings to bad contact with the HRM sensor. It was more humid this morning and my HR showed normal levels, so I'm convinced that's the reason.


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