Tracking steps on Treadmill Desks.

What workout should you use to track steps when using a 'Treadmill Desk' when your hands don't move (stationary on desk/keyboard) but your feet do?

Nothing I do seems to work. The app that sends data to Apple Health doesn't get pulled into Activity/Fitness... although it's in Apple Health.

Currently I'm trying 'Stair Stepper' - which I assume compensates for little to know hand movements. Thoughts?