What’s the difference between the “Indoor Walk” and “Indoor Run” workouts? The Apple Watch supports workouts called Indoor Walk, Indoor Run, and Indoor Cycle, and it also has Outdoor versions of these. The Apple Watch User Guide explains that


  Outdoor and Indoor Walk/Run/Cycle are distinct workouts because Apple Watch calculates the calorie burn differently for each. For indoor workouts, Apple Watch relies mainly on your heart rate readings for calorie estimates, but for outdoor workouts, Apple Watch works in conjunction with iPhone (which has GPS) to calculate speed and distance.


But it doesn’t explain the difference between e.g. Indoor Walk and Indoor Run. When I use a treadmill I go for long walks interspersed with some running. Which Indoor workout is more appropriate for tracking this kind of exercise?
If it's a mixture of run and walk; go with indoor run. The sensors pick up your jogging stride differently when it knows your running so it will be more accurate when it expects your arms to be in a run position.