The upper and lower limbs are attached to an anatomical structure called the trunk, commonly known as the torso. The trunk is composed of several regions called the thorax, abdomen, pelvis, and back. Running through the center of the back is the vertebral column which contains the spinal cord. Large back muscles such as the trapezius, latissimus dorsi, and rhomboids as well as deeper, smaller ones are attached to various points of the vertebral column. The musculature of the back helps you maintain your posture, bend your trunk, move your arms, shrug your shoulders, and much more.
Large abdominal muscles, for example the rectus abdominis also contribute to the trunk. This is the famous ‘six-pack’ that many fitness enthusiasts strive for.