Stand upright with hips wide apart (starting position, then one leg always moving freely), alternately lift one knee straight up to navel height and lower it back to the standing position, the arms swing along and support the movement (knee lift in place). The rhythm/intensity can be varied.

Attention:
Keep your upper body stable/upright, actively support the movement with your arms.

Lighten:
Lift your knees less high; slower execution (reduce rhythm/intensity).

Harden:
Lift your knees higher; fast execution (increase rhythm/intensity); additional weight on your legs (hold in your hands).

Variant I:
Execute the movement very slowly and linger briefly in the one-legged stance to further improve your balance.
Variant II:
Arms folded behind the head, elbows crossed towards the raised knee.
Variant III:
Knees turned out to the side when lifting, arms swinging more to the side.