Start standing with your feet hip-width apart, hands clasped in front of your chest. Bend your knees to lower into a squat. This is the starting position.
Step your right leg back behind you to place your right knee on the floor. Then repeat with the left leg.
Step your right foot forward to plant it on the floor in front of you, then repeat with the left leg so you return to a squat. (Don't stand up completely.) That's one rep.
Repeat for 45 seconds, alternating the leg you lead with.