Lumbar spine

The lumbar spine is the lower back: five vertebrae, numbered L1 to L5, between the bottom of the ribcage and the pelvis. Together they form a gentle inward curve, the lumbar lordosis. Above it sits the thoracic spine and below it the sacrum, and the lumbar spine has to combine carrying weight with letting you bend, straighten and turn (Waxenbaum et al., 2026).

What is the lumbar spine made of?

• Vertebrae. Each vertebra has a body at the front, which takes most of the load passing down the spine, and an arch at the back that encloses the spinal canal. Lumbar vertebrae have large bodies, and L5’s is the largest in the spine. Its front is taller than its back, which helps form the angle where the spine meets the sacrum (Waxenbaum et al., 2026).
• Discs. An intervertebral disc sits between each pair of vertebral bodies. Discs get thicker further down the spine, so the lumbar discs are the tallest (Waxenbaum et al., 2026). Their gel-like core is the nucleus pulposus.
• Facet joints. Pairs of small joints at the back, the zygapophyseal joints, keep the vertebrae aligned, limit how far they move and bear weight in some positions. In the lumbar spine their joint surfaces are mostly upright and curved (Waxenbaum et al., 2026).
• Nerves. The discs and the bony parts of neighbouring vertebrae form the openings where spinal nerves leave the spine (Waxenbaum et al., 2026). There are five pairs of lumbar nerves (Kaiser & Lugo-Pico, 2023); where each leaves the spine is its nerve root.
• Muscles. The erector spinae run along both sides, and beneath them the multifidus, which is most developed in the lumbar region (TeachMeAnatomy).

What sitting does to the lumbar spine

Sitting changes the shape of the lower back a lot. In an X-ray study of eight men, imaged standing and then sitting in a car seat, the lumbar curve and the tilt of the sacrum both fell sharply, and every lumbar joint bent forward, most of all between L4 and L5 (De Carvalho et al., 2010). What that does to the discs is covered under nucleus pulposus.

A changed shape is not the same as harm. A review of 41 systematic reviews found associations between sitting, posture and low back pain, but no consensus that they cause it (Swain et al., 2020). Time still seems to matter: among 250 people who had just recovered from an episode of low back pain, sitting for more than five hours a day was one of the things that predicted it coming back within a year (da Silva et al., 2019). Chair setup is covered in office chair setup, and the wider picture in lower back pain from sitting.

Why scans of the lumbar spine often mislead

Signs of wear show up on scans of people who have no pain at all. Across 33 studies of 3,110 pain-free people, disc degeneration was found in 37% of 20-year-olds and 96% of 80-year-olds, and disc bulges in 30% and 84% (Brinjikji et al., 2015). This is one reason NICE advises against routine imaging for low back pain outside specialist settings (NICE NG59), and why most lower back pain is classed as non-specific low back pain.

When to see a doctor

See a GP if back pain hasn’t improved after a few weeks, is worse at night or when you cough or sneeze, or comes with weight loss or a lump. Ask for an urgent appointment or contact NHS 111 if you feel hot, shivery and unwell, or the pain is severe and worsening quickly. Call 999 for pain, numbness or weakness in both legs, loss of feeling around the genitals or anus, or changes in bladder or bowel control (NHS).

Bavelu’s lower back sessions are designed and filmed by physiotherapists; one of the exercises is on lower back stretches.