Arch-Up The arch-up, also known as a Superman, works your posterior core muscles. Lie face down on your stomach with your arms and legs extended. Keep your neck in a neutral position. Keeping your arms and legs straight (but not locked) and torso stationary, simultaneously lift your arms and legs up toward the ceiling to form an elongated "U" shape with your body — back arched and arms and legs lifted several inches off the floor. Hold for two seconds and lower back down to complete one rep. Carey recommends doing 25 to 30 reps. Image Source: POPSUGAR Studios