As a supplement to my other workouts, I briskly run up and down several flights of stairs. Would the Stair Stepper Workout be an accurate calibration for that? If not, what should I use?
Apple Watch Series 3, watchOS 4.3
Your best option is to try it and see how it looks, but I suspect you will get problems with needing to put in more time to complete the workout. Compare with same activity in default mode without selecting a workout. Personally I usually ignore workouts and just go with default mode, it seems to work better for my activity pattern.
Stair Stepper workout vs regular stairs
