Rectus Abdominus muscle

Pictured above is the Rectus Abdominus muscles which makeup one segment of the four muscles of the abdominal group. The Rectus Abdominus muscles are the muscles most often referred to as the "six pack" (there are eight sections, but there are only six exposed) or "rock hard abs" in the fitness commercials. These muscles have fibers that run in a vertical direction and have attachments to the bottom of the ribcage, top of the pelvic girdle, and the internal and external oblique muscles on each side of the body. This vertical orientation of force lifts and holds the pelvis in position and reduces the load on the lumbar vertebrae. When this muscle group is weak the pelvic dips downward, thus creating excessive curvature in the lumbar spine. This in turn results in increased force on the back or posterior joints of the lumbar vertebrae. Demonstrating the importance of core training exercising for achieving strong muscle tone in these muscles.