For these stomach exercises you start by lying on your stomach on the floor or another flat surface. We'd recommend using a mat or a thick towel to protect your knees and hips. Rest your upper body on your forearms. Your elbows should be at about a 90 degree angle, positioned underneath your shoulders. Using your torso muscles lift your body until you are supported only by your toes and elbows. make sure that your body remains rigid, hence the name of the board. Hold the position for at least twenty seconds. This should exercise your muscles enough that you shouldn't need to do repeat reps.