I usually only wear my Polar GPS watch during my training sessions. I like the simplicity of it, but of course I worry about its accuracy in measuring my heart rate. The watch is good for reporting relative effort between sessions, but now that I’d like to do some heart rate zone based training, is it good enough?

I did an interval training session with my chest strap for comparison purposes. I was a little surprised that the results were so different. Polar states that the wrist measurement is “not necessarily accurate”: What are the pros and cons of different methods for measuring heart rate?

My run consisted of three 4-minute intervals followed by an easy jog. The shape of the curves is similar enough to tell when the intervals occurred, but the watch reports strangely high (incorrect?) heart rates for the easy part of the run. I wonder if this inaccuracy is too bad for training guidance? DCRainmaker has written interesting articles on the same subject: Polar Verity Sense (Optical HR Sensor Band) In-Depth Review (or even the old Troubleshooting your heart rate monitor/strap HR spikes). His results from the different measurement methods seem to be much closer. Why is that? I used the Polar Vantage M and the Wahoo TickrX. And yes, both were worn correctly, i.e. tightly :)

I used the FitParse Python package to parse the HR values from Wahoo’s .fit file. Polar allowed export to .csv so no further parsing was required. Then just some Pandas dataframe and time series mangling to get the data aligned and formatted for creating a graph.