The short answer
- A systematic review of 19 studies found low back pain less common in runners than in the general population and than in other athletes, and suggested running may be protective.
- Runners have better disc hydration and proteoglycan content than non-runners, and larger discs. The loading associated with it was slow running and fast walking, not high impact.
- Disc bulges and degeneration are found in large numbers of people with no pain at all, and the proportion rises steadily with age.
- Most running-related back pain behaves like ordinary back pain: it settles, it responds to movement, and it does not need a scan.
- Pain travelling below the knee, numbness, weakness, or any change in bladder or bowel control is a different category and needs assessing.
If your back hurts and you run, somebody will tell you that running is the reason. It is the most intuitive story in the world: repeated impact, a stack of discs, wear. The research does not support it, and the direction it points instead is genuinely useful.
How common it actually is
Back pain is the most common musculoskeletal complaint there is. Runners get less of it than people who do not run. That is not proof that running protects the spine, because runners differ from non-runners in many ways at once, but it is the opposite of what the wear story predicts.
What running appears to do to discs
That is the first human evidence that discs respond positively to exercise, and it points at a fairly ordinary running pace as the thing associated with the effect. The loading discs appear to like is rhythmic and moderate rather than maximal.
What a scan will find
The same thing it finds in people who feel fine.
At forty, a scan of your back will probably show something. So would a scan of the back of the person next to you who has never had a sore day. That is why a finding on a report is not by itself an explanation, and why a scan early in an ordinary episode tends to add worry rather than information.
What it usually is, and what to do
Most running-related back pain behaves like back pain anywhere else: it is uncomfortable, it is frightening out of proportion to its seriousness, it responds to movement, and it settles over weeks.
The practical adjustments are small. Keep moving, including running, at whatever dose does not leave you worse the next day. Cut the sessions that provoke it most, which for backs is often the longest run rather than the fastest. Keep the strength work going, because trunk and hip strength is the capacity side of the same equation that everything else on this site runs on.
What does not help is bed rest, bracing yourself rigidly while you move, or waiting until it is completely gone before running again.
When it is not ordinary back pain
Running-related back pain is usually the boring kind. A few patterns are not, and they are worth recognising rather than pushing through.
Pain that travels below the knee in a defined line, with numbness or pins and needles, suggests a nerve root is involved rather than the back alone. That often settles too, but it changes the timeline and it needs assessing rather than guessing.
A small tender spot on bone in the lower back or the sacrum, in a runner who has increased load quickly, is the pattern we take seriously. Bone stress injuries occur there as well as in the leg, and the sacrum is a site where they are easy to miss4.