Massage & Bodywork Licensing Examination (MBLEx)

Which movement will shorten the fibers of the rectus abdominis?

1. Extension

2. Flexion

3. Rotation

4. Pronation

The correct answer is: Flexion

The shortening of the fibers of the rectus abdominis occurs during flexion of the torso. This muscle is primarily responsible for flexing the lumbar spine, which is the movement involved in bending forward. When you perform a flexion movement, such as doing a sit-up or bending at the waist, the rectus abdominis contracts, pulling the ribcage closer to the pelvis. This contraction is what effectively shortens the muscle fibers. In contrast, extension would lengthen the rectus abdominis as it would involve straightening the torso or arching the back. Rotation involves twisting the torso, engaging different muscles, and does not primarily shorten the rectus abdominis in the same manner as flexion. Pronation typically refers to the rotation of the forearm and does not involve the rectus abdominis, thus it also wouldn’t lead to shortening of its fibers. Understanding these movements and their effects on muscle contraction is essential for applying effective techniques in therapeutic and sports settings.