The lumbar vertebrae are the largest movable bones of the backbone. Their large size and bone strength is necessary because these vertebrae support more weight than the upper two segments of the backbone. While muscles and other tissues assist, the lowest portion of the vertebral column—known as the lumbar spine—provides support as you bend, twist, and extend your upper body.
In addition to providing postural structure and facilitating movement, the vertebral column provides protection for the spinal cord, a long tube of nervous tissue connected to the brain. Branches of the spinal cord spread to all regions of the body to communicate information to and from the brain.
The lumbar spine consists of five vertebrae in most people (a small minority have six), and these are the largest vertebrae of the spine because they bear the most weight.
The vertebrae of the lumbar spine are numbered L1 through L5; the “L” stands for “lumbar.” They are:
- L1: This vertebra begins the lumbar spine after the thoracic spine ends.
- L2–L4: These vertebrae are the middle of the lumbar spine.
- L5: This is the last vertebra of the lumbar spine and connects to the sacrum.
A rubbery pad between each vertebra protects them from grinding against one another and creates a small joint that makes movement possible. Called intervertebral discs, these pads absorb shocks and distribute pressure on each vertebra. These discs can become damaged, whether through injury or deterioration, and this often causes long-term pain.
Below the five lumbar vertebrae lies the sacrum. It consists of five vertebrae that fuse together as you mature to create a singular triangle-shaped bone. The sacrum is wedged into the space in the back of the pelvis at the hips.
The coccyx is last section of the lumbar spine as well as the spinal column. Better known as the tailbone, it is composed of three to five fused vertebrae. It is considered a vestigial tail, or one that lost its function as humans evolved. The coccyx serves as an anchor for several tendons and ligaments, and acts as a stabilizing tripod when you sit.