“Running causes knee and hip arthritis”

A 2017 review pooled 25 studies covering 125,810 people and compared runners with people who did not run. Hip or knee arthritis showed up in 3.5% of recreational runners, 10.2% of the non-running comparison group, and 13.3% of competitive runners - those racing at professional or international level [1].

A 2024 survey of 3,804 Chicago marathon runners found hip or knee arthritis in 7.3% of them, and none of the running measures predicted who had it: not years spent running, not the number of marathons finished, not weekly mileage, not pace. What did predict it was age, body mass index (weight relative to height), a family history of arthritis, and a previous hip or knee injury or operation [3].

The idea that each stride wears cartilage down like tread on a tyre does not survive contact with the scans. A 2022 review of 43 studies that imaged runners' joints before and after running found that knee cartilage does thin briefly straight after a run - changes the reviewers put down to fluid moving out of it - but the changes do not last, and repeated running did not produce new cartilage damage [2].

The picture is least reassuring at the extreme end: competitive runners in the pooled review had the highest rate of the three groups, at 13.3% [1]. In the marathon survey, though, how much a person ran still made no difference to whether they had arthritis [3].

All of this is observational - it compares people who chose to run with people who did not, so it cannot prove that running itself protects a joint. The authors of the pooled review say so directly, noting that a previous injury or other differences between the groups could explain part of the gap [1].

It also says little about someone who already has significant joint damage, since everyone surveyed was by definition still running. Anyone in that position is better guided by an orthopaedic specialist, and a sudden jump in mileage carries its own injury risk that is separate from long-term arthritis.

For someone running at an ordinary recreational pace, the fear is not supported by the evidence: running is associated with healthier hips and knees, not damaged ones.