Start in a plank position. Cheat your right leg toward your centre line, and lift your left leg off the ground so your heel is even with your pelvis.
Keeping your torso steady, reach your right arm forward. Really brace through the abs by pulling your navel to your spine. Hold this position for 10 seconds.
Keeping your torso stable, bring your right elbow to your left knee under your body. Do not round your back or twist your spine, and keep your pelvis down. Then reach the arm and leg out and away from each other. This counts as one rep.