Does your GPS watch report bizarre, dramatic spikes in heart rate in the middle of your run? I received a text message from a friend recently with this screenshot of his heart rate and elevation data from an easy run:
This was from a typical run on pretty mild to moderate hills. At first glance, you might think that running uphill triggered an abrupt increase in heart rate, but unless this coincided with an abrupt surge in speed, such a big spike in heart rate seems very strange.
Looking at this plot, it seems like one of two things is happening: either (a) my friend’s watch is seriously mistaken about his heart rate, or (b) my friend should see a cardiologist.
Even though companies like Garmin or Apple or Fitbit keep their data processing algorithms pretty close to the chest, my PhD research involves a lot of work with wearable technology, so I have a pretty solid understanding of what’s going on under the hood when a GPS watch is estimating things like running speed or heart rate. What could be going wrong here?