Begin on all fours with your hands directly under your shoulders and your knees directly under your hips.
Pull your abs in to your spine. Keeping your back and pelvis still and stable, reach your right arm forward and left leg back. Don't allow your pelvis to rock side to side as you move your leg behind you, and don't let your rib cage sag toward the floor. Reach through your left heel to engage the muscles in the back of your leg and your butt.
Return to the starting position, placing your hand and knee on the floor. Repeat on the other side.
This counts as one rep. Complete two sets of 10 reps.