Start in a traditional plank position with your hands under your shoulders and your body in one straight line.
As you bend your elbows to lower your torso into a push-up, bend your left knee to touch your left elbow. Keep going down until your chest touches the floor. Right when your chest touches the floor is when your knee should meet your elbow.
As you straighten your arms, return to plank position bringing your left foot next to your right. If this is too difficult, instead of simulataneously doing a push-up and the knee-to-elbow touch, do a complete push-up and when you return back to plank, touch your left knee to your left elbow.
Repeat this move on the other side. This counts as two reps. Complete four sets of 12 reps (six on each side).