Your abdominals, commonly called abs, consist of several muscle groups, all located in the midsection, just below your chest to your pubic bone. These include: rectus abdominis which is made up of upper, middle, and lower abs; transverse abdominis; and the obliques. The upper, middle and lower abs start near the middle of your sternum and runs vertically to the lower part of the pelvis; they are responsible for flexing the vertebral column or helping you curl your trunk as you would when doing crunches or sitting up in bed. The transverse abdominal muscles run horizontally and are the deepest muscular layer of the abs; they run around your body like a girdle and help compress and support internal organs. The obliques are the muscles that make up your waist and consist of two smaller groups: the external obliques and the internal obliques. The external obliques are the muscles of the upper and outside part of your waistline; they start just under your chest, on your lower eight ribs, and are responsible for helping you twist and bend sideways. The internal obliques are located beneath the external obliques; they also helps you twist. It is important to have strong abdominals for most all motions, including common day-to-day activities. In addition, most low-back pain is attributed to weak abdominals.