Understanding Trunk Anatomy

To begin a discussion on the bones of the trunk, we have to start with the spinal column, which is the basis or core for our entire body. The bones that form the spinal column are the cervical vertebrae (neck), the thoracic vertebrae (upper back to midback), and the lumbar vertebrae (low back). Sandwiched between vertebrae are the intervertebral discs that provide shock absorption and stability to the spinal column. These discs can become injured and cause significant pain and disability. The top of the spinal column is attached to the skull, and the lower end of the column attaches to the sacrum and coccyx. The sacrum is encircled by the pelvis, which has a receptacle on each side for the head of the femur (thigh bone). The ribs attach to the thoracic vertebrae in the back and the sternum in the front. However, some ribs are called false or floating ribs, because they do not attach directly to the sternum but attach by cartilage to the other ribs to help form the entire rib cage.

The trunk muscles on the back of the body are built in layers upon layers. The muscular layers are necessary and practical, because as a group they help stabilize the trunk in all planes of movement and provide additional protection to the spinal cord. Their primary job is to hold the body upright against gravity, but they also extend and rotate the neck and trunk. The numerous muscles throughout the back are named for their action, like the erector spinae (spinal extension) and rotators (spinal rotation); or for their origin and insertion point, like the semispinalis thoracis (which originates on the transverse process of the thoracic vertebrae and inserts on the spinous process of the thoracic vertebrae). The quadratus lumborum covers the area where your kidneys are and is involved in side bending and hip hiking.

The trunk musculature on the front of the body is collectively known as the abs, but actually there are a few different abdominal muscles that work together. The muscle that is known as the six-pack is the rectus abdominis (RA). It flexes the trunk so that the rib cage moves toward the pelvis. It covers the so-called corset of your trunk, the transverse abdominis, which is responsible for keeping your internal organs internal. The external oblique muscle fibers stretch diagonally over each side of the trunk laterally and rotating it to the other side when working unilaterally. The external oblique muscle fibers run in opposite direction from the internal oblique muscle fibers. In addition to assisting the rectus abdominis with trunk reflection, they are lateral flexors and rotate the trunk to the same side.

Anatomy of the abdomen

The trunk musculature is closely associated the with hip and butt musculature. Whereas the trunk muscles attach to the top of the pelvis, the hip and butt muscles attach to the sides and bottom of the pelvis. They all need to be strong for stabilization, and they have to work in unison. Sometimes core exercises include hip and butt components for this reason.