Lumbar vertebrae (L1–L5)
Five large vertebrae form the lower back's bony column, progressively increasing in size toward the pelvis to handle greater compressive load.
The lumbar spine's five vertebrae are the largest in the spinal column, built to bear substantial compressive load while still permitting bending, extension, and rotation. Thick intervertebral discs between each vertebra act as shock absorbers and allow controlled movement across the segment.
A layered system of muscles, from deep segmental stabilizers to large superficial extensors, works together with the abdominal wall and hip muscles to control movement and protect the spine during lifting, twisting, and prolonged postures.
Key structures
Intervertebral discs
Thick fibrocartilage discs cushion each lumbar segment and allow bending and twisting; their outer fibers can tear under repeated or heavy loading, sometimes leading to herniation.
Erector spinae
This group of long muscles running along the spine extends the trunk and controls forward bending, and is one of the most commonly strained muscle groups in acute low back pain.
Multifidus
Small, deep muscles spanning individual vertebral segments provide fine control and stability, and are frequently found to be inhibited or deconditioned in people with recurrent low back pain.
Transversus abdominis
This deep abdominal muscle wraps around the trunk like a corset, working with the multifidus to stabilize the spine before limb movement occurs.
Sciatic nerve and lumbar nerve roots
Nerve roots exiting the lumbar spine combine to form the sciatic nerve, which supplies the back of the leg; compression of these roots produces the radiating pain known as sciatica.
Planes & range
Forward flexion is the lumbar spine's largest single motion, though a substantial portion of what looks like low back bending actually occurs at the hips, a distinction clinicians assess when evaluating movement patterns.
The lumbar spine's combination of load-bearing bone, shock-absorbing discs, and layered stabilizing muscles explains why low back pain can arise from many different tissues, and why treatment often addresses movement patterns and strength rather than a single structure.
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