On a hard floor, place the balls of your feet on a towel or sliders and come into a plank position. Align your wrists under your shoulders, with your hands spread shoulder-width apart. Your spine should be neutral.
Pull your knees into your chest with a slow, four-count tempo, without arching your hips. Maintain a flat back. Return to the starting position with the same four-count tempo. This counts as one rep.