I've done two HIIT workouts (outdoor boot camp) with it and it was interesting to see the heart rate graph afterward. I don't think it engages GPS because there's no map showing your movements like when you choose running. But it did tell me I moved 2.3 miles over the course of the hour (lots of sprints). I do wish I had a map, though, and wonder if I would be better off choosing run instead. That seems to give you more information. In one hour my battery dropped about 20%. A couple times I glanced down and it was having trouble reading my heart rate, but overall I had a pretty complete graph of it going up and down and says I burned 430 calories.