Position a box behind you and stand with feet shoulder-width apart with your arms raised at shoulder-level in front of you.
Raise one leg slightly in front of you while keeping it straight and balance on the leg that remains on the ground.
Inhale and break at the hips, sitting down and back in the direction of the box while simultaneously bringing your raised leg forward as you squat down.
Continue until your butt makes contact with the box while your raised leg is still in the air.
Exhale and press through your heel and midfoot while keeping your foot firmly planted until you stand upright, returning to the starting position.
After all reps are completed, switch sides and repeat the movement. 10 reps prescribed means you should perform 10 reps on each side (20 total).