Get into basic push up position. Place the feet on a stable elevated surface. Arms should be slightly wider than shoulder width, core tight. You want your body to form a straight line from your shoulders to your hips to your ankles, with your neck in line with your spine.
Keeping your core strong and engaged, bend your left knee and rotate it toward your right side and exhale. Do this in a very controlled manner and only go as far as comfortable.
Return left foot to the starting position.
Now with core still engaged raise your right foot and rotate your right knee toward your left leg. Exhale. Return to start position.