Saturday, 29 October 2016

Resting Heart Rate and Fitness

Previously I've done plenty of posts on using Fitbit Heart Rate data, Strava data and suchlike to assess my fitness.

Two things I've spotted recently:

  1. My resting heart rate seems to be decreasing, as shown on my Fitbit Charge HR.
  2. I seem to be running consistently faster at parkrun.

Conventional wisdom is that a lower heart rate represents improved fitness.  So to find out whether the two are linked...

The analysis was pretty simple.  First I just scraped monthly average resting heart rate data from my Fitbit app and noted it in Excel (I didn't think I'd need the power or R for this analysis).  This nicely smooths out day-to-day variations in heart rate and shows some decent trends.  Example:

I also scraped all parkrun results from the parkrun website.  I chose to use parkrun for this analysis as it's the same distance run at the same time every week in (almost) the same place.  There are some variables that could affect my time (e.g. if it's muddy underfoot, the odd bit of tourism) but these things should cancel themselves out if you take enough data points and allow trends to be spotted.  An example of the data:

With some Excel jiggery-pokery I managed to get resting heart rate (blue line) and park run times (orange dots) on the same chart.  Here it is:

I like this chart as it tells a real story of the correlation between heart rate and fitness (or low parkrun time).

  • On the left hand side you can see when I first got my Fitbit, my resting heart rate was between 65 and 70 BPM and my parkrun time was ~21 minutes.  
  • I then got injured in summer 2015 and there was a gap when I didn't run at all.  At the end of this my resting heart rate was over 70 BPM so I was relatively unfit.
  • I then made a comeback in Autumn 2015, started running regularly and by Spring 2016 had a sub 60 resting heart rate and was running sub 20 minute parkruns.
  • Then the summer 2016 came and for various reasons (holidays, kids' activities, doing cycling) and my heart rate crept up to nearly 60 BPM and my parkrun time went back to the ~21 minute realm.
  • Then most recently I've done a strong block of focused running training, my heart rate is at 55 BPM (lowest ever recorded) and I'm back to 20 minute and sub 20 minute parkruns.

I love graphs like this!  My view is that running is an "honest" sport, the more you put in the more you get out, and this graph underlines this point.