I usually run with a Garmin watch, but today I thought I'd try the workout app. Had my phone in my pocket with Strava running (can't see any other way to get the GPS track out of the Apple app). I set the app for 4 miles, but whilst I was out decided to do a bit extra and ended up doing what I know from Garmin is a 4.5m run. Strava had 4.5m, but the watch app says 4.13m. They're both measured off the phone's GPS, so I'm unsure why the watch would be so far out? As I can't see any way of getting the data out of the Apple app and into Strava, Garmin Connect etc I'll probably stick to running with my Garmin, but it seems odd that the data is so far out.