Does running wear out your knee joints?

Short answer

No. Knee cartilage was squeezed by 3 to 5% right after a run and then recovered, and arthritis in recreational runners was 3.5%, lower than in non-runners (10.2%). What separated people with arthritis was age, body weight and past injury, not distance run.

Does running wear out your knee joints?
'The more you run, the more your cartilage wears down' — does this formula hold?
Every landing sends a jolt through the knee, so many people say years of running wear down cartilage and lead to arthritis. We checked whether that impact really wears cartilage down, using knee scans and large surveys.
Cartilage gets squeezed right after a run
Thickness dropped 3 to 5%, then came back
An analysis of 24 studies that scanned 446 knees with MRI found knee cartilage thickness and volume fell by 3.3 to 4.9% right after running. The signal that reflects cartilage condition returned to normal within 91 minutes. Existing cartilage damage did not change in the 48 hours after running.
Does it add up over years?
In 18 years of follow-up, there was no more arthritis
Knee X-rays were taken from 1984 to 2002 in 45 long-distance runners and 53 non-runners. At the end, arthritis was 20% in runners and 32% in non-runners, and severe arthritis was 2.2% and 9.4%. Runners did not have more.
Looking at large numbers of people
Recreational runners had less arthritis
An analysis that pooled 114,829 people found hip and knee arthritis in 3.5% of recreational runners and 10.2% of non-runners. Only people who ran at international competition level came out higher (13.3%). Running for less than 15 years put arthritis risk at 0.6 times that of non-runners.
Distance and pace made no difference
Age, body weight and past injury separated people with arthritis
Among 3,804 marathon runners, 7.3% had arthritis. Years of running, number of marathons, weekly distance and pace were not linked to arthritis; age, body weight, past knee injury or surgery and family history were. An analysis of 12,273 people also found no more arthritis in those running over 48 km a week.
Comparing cartilage directly on MRI
The difference came from body weight, not running
183 people matched by age and sex were split into runners, non-runners and people with a BMI of 30 or more, and their knees were scanned. Runners and non-runners did not differ in cartilage shape or knee function. The BMI 30+ group had up to 4 times more cartilage abnormalities.
If you already have knee arthritis
Runners' knees did not get worse
In 1,203 people with knee arthritis followed for 4 years, worsening arthritis and new knee pain in runners did not differ from non-runners (0.9 times). In fact, frequent knee pain went away 1.7 times as often.
Summary: running did not wear out the joints
Squeezed cartilage recovers, and arthritis was less common
Cartilage squeezed by 3 to 5% after a run recovered, and a survey of 2,637 people found no more painful arthritis in runners. What was linked to arthritis was age, body weight and past injury. There was no evidence that recreational running wears out the joints.