RESISTANCE Abs Abdominal crunches MUSCLES WORKED: Rectus abdominus Alternative names: Ab crunches Lie flat on an exercise mat, knees bent and feet flat on the ground. Cup your hands at the sides of your head or cross your arms on your chest. Use your abdominal muscles to lift the upper body closer to the legs. Return slowly to the original starting position. Repeat the exercise. - Don't arch your back. - Keep your navel pulled in. - Keep movements slow and controlled. - Don't use your hands to lift your head.