Flexion

Flexion is the anatomical term for a bending movement that decreases the angle between two body parts. When you bend your elbow, the forearm and upper arm come closer together; when the knee flexes, the heel moves towards the buttock. The opposite movement, which opens the angle again, is extension (TeachMeAnatomy).

Flexion in the spine, neck and hips

Flexion and extension both happen in the sagittal plane (TeachMeAnatomy). In the spine and neck, that means bending forward and back. Applied to the places that matter at a desk:

• Spinal flexion is rounding the back forward. Slumping in a chair takes the lower back towards the end of its flexion range; researchers measure exactly this “end-range lumbar flexion” during slumped sitting (Hoffman et al., 2012).
• Neck flexion is bending the head forward, as when you look down at a laptop or phone.
• Hip flexion brings the thigh and trunk closer together. Every time you sit, your hips are flexed, which is why the muscles that do it are called the hip flexors.

The cat-cow stretch is a simple picture of both directions: rounding the back is flexion, arching it is extension.

Is spinal flexion bad for your back?

“Don’t bend your back” is one of the most repeated pieces of back advice. The evidence is less clear-cut.

• Lifting. A meta-analysis of lifting studies found low-quality evidence that bending the lower back more during lifting was not a risk factor for developing or keeping back pain. Nine of 11 studies found no difference in lumbar flexion between people with and without back pain; where a difference appeared, people with back pain bent their lower back slightly less (Saraceni et al., 2020).
• Disc pressure. In one 45-year-old volunteer with a pressure sensor in a lower lumbar intervertebral disc, pressure was higher when sitting fully rounded (0.83 MPa) than when sitting without a backrest (0.46 MPa), and higher when standing bent forward (1.1 MPa) than standing relaxed (0.5 MPa). The authors concluded that constantly changing position helps fluid, and with it nutrition, flow into the disc (Wilke et al., 1999). One person is a very small sample.
• Back muscles. In most people the back muscles, the erector spinae, switch off at the end of a full forward bend, which is called the flexion relaxation phenomenon. In a meta-analysis, about 55% of people with chronic non-specific low back pain kept those muscles working instead (Gouteron et al., 2022). That describes how people with back pain move; it doesn’t show that bending caused the pain.

One group does need care. With osteoporosis, the Royal Osteoporosis Society says bending forward is still a normal part of everyday life, but some exercises that load a rounded spine, such as sit-ups and touching your toes, may need adapting to lower the chance of spinal fractures (Royal Osteoporosis Society).

Neck flexion at a desk

A three-year study of 1,334 workers used video recordings to measure how they held their necks at work. People who worked with the neck bent forward at least 20 degrees for more than 70% of the time showed a trend towards more neck pain, but it was not statistically significant. Sitting for more than 95% of the working day was linked with neck pain (Ariëns et al., 2001). Studies of phone use have reached a similar verdict on the angle alone; see text neck. If you work on a laptop, the setup side is covered in working on a laptop without straining your neck.

When is pain on bending a reason to see a doctor?

Pain when you bend after a long day at a desk has many possible causes; lower back pain from sitting covers the usual ones. See a GP if back pain isn’t improving after a few weeks or painkillers aren’t helping. Call 999 or go to A&E if back pain comes with numbness around your bottom or genitals, loss of feeling in one or both legs, or problems controlling when you pee or poo (NHS).