Lie on your back with feet hip-width apart, knees bent at 90 degrees with hands behind ears [A]. Exhale as you contract abs and lift torso up towards thighs. Ensure back is straight. Clench fists and extend left hand towards the right with control, rotating palm to face down [B]. Snap left arm back to starting position. Repeat on the other side. Lower your back down slowly to complete one rep.