I have been doing some tests with my Apple Watch and Workout app. I think the results were very good.
The test consisted in to complete the same distance with three differents ways and compare how the Apple Watch calculate the results.
These was the tests and results:
Test 1: A lap running arround my house block, with Outdoor Run selected and my iPhone with me (Apple Watch receiving GPS data).
Total Distance: 0,44 Km.
Total Time: 02:21
Active Calories: 22 (4 Resting, 26 Total)
Avg Pace: 5'17'' KM
Avg Heart Rate: 148 LPM
Test 2: The same lap arround my house block, trying to do it in the same time, but selecting Indoor Run and without iPhone (Apple Watch without GPS data).
Total Distance: 0,45 Km.
Total Time: 02:06
Active Calories: 24 (3 Resting, 26 Total)
Avg Pace: 4'38'' KM
Avg Heart Rate: - (Not calculated, I think it was an error)
Test 3: The same lap again, selectiong Indoor Run without iPhone (Apple Watch without GPS data) but this time alterning running and walking diferent sections.
Total Distance: 0,44 Km.
Total Time: 03:24
Active Calories: 24 (5 Resting, 29 Total)
Avg Pace: 7'38'' KM
Avg Heart Rate: 144 LPM
CONCLUSIONS: As you can see, the Apple Watch calculated the same distance, with and without GPS, even I tried to cheat it walking some sections and running others. Perhaps I need to test it more time with longer distances, but I can conclude that the Apple Watch calculates the distances very good even without GPS.
So for my purposes I think "Indoor Run" perhaps is a good option to use when practicing sports like basketball, soccer or tennis, because the Apple Watch seems to know when we are running, walking or resting and taking a breath.
The only thing is that the Apple Watch don't consider the energy we use in every shoot, but I supose this elevates our Heart Rate so the calories will be calculated according to this extra effort too.
I was using the Apple Watch in my first futsal match (in a little field) and these have been the results:
Total Distance: 5,47 Km.
Total Time: 1:07:08
Active Calories: 246 (105 Resting, 351 Total)
Avg Pace: 12'15'' KM
Avg Heart Rate: 133 LPM