A strong tendinous sheath called the "linea alba," or white line, divides the rectus abdominis down the middle, and three more horizontal tendinous sheaths give the muscle its familiar "washboard" look in very fit athletes.
The rectus abdominis helps to flex the spinal column, narrowing the space between the pelvis and the ribs. It is also active during side bending motions and helps stabilize the trunk during movements involving the extremities and head.
