Stand between two benches, one to each side. Hold dumbbells in each hand down to sides
Lift leg and place foot on bench to side slightly forward of straight knee. Stand on bench by straightening leg and pushing body upward. Step down returning feet to original position. Repeat with opposite leg alternating between legs.
Keep torso upright during exercise. Stepping knee should point same direction as foot. A modest degree of knee rotation occurs during this movement. See Controversial Exercises and Rotary Force in Squat Analysis.