title: How to detect whether an athlete is in play or on the bench indoors via the Apple Watch?
body: <p>My goal is to detect whether an athlete is in play on the field or on the bench and then segment these time frames into "shifts" or "bench time" using the Apple Watch.  As I see it I have 3 options: </p>
  
  <p>(1) Core Motion and the accelerometer.  I haven't tested yet but my concern here is the accuracy of detecting play vs. bench, given that a player might still make hand movements on the bench making this difficult to parse between.  </p>
  
  <p>(2) Heart Rate.  While possible to make a distinction based on heart rate, my concern here is the variability of athletes' heart rates, i.e. one player might max out at 190bpm while another might play at the same level at 150bpm, even if I were to use % difference of heart rate to determine play vs. bench I might not accurately account for situations where the difference was minor, i.e. young children's games. </p>
  
  <p>(3) Core Location and GPS.  My concern here is (1) most of the time my athletes are indoors, and I am not sure of the accuracy of GPS in current iterations of WatchOS when indoors to detect whether an athlete is moving vs. non-moving?  Another difficulty is that Apple Watch's only started shipping with onboard GPS in Series 2, and for series 0-1 I think that the distance of an athlete's phone (i.e. in the locker room) from the watch would be problematic.  </p>
  
  <p>Has anyone else dealt with a similar challenge and/or have any thoughts as to how best to approach the above? </p>