I have used "walking desk" setup now for about a year. Treadmill is kind of special walking treadmill, speed ranges from 1-5 km/h (0.5km/h steps). I normally walk about 5-6km per day while working. Mostly speed is 1 or 1.5km/h.

Only downside is that when having video meeting, my head is bouncing while walking. Usually leads the conversation on treadmill.