TLDR;
Running doesn't cause osteoarthritis and doesn't thin your cartilage, and even better:
In people who already have knee arthritis, it actually improves knee health.
Knee pain is generally a chain reaction from further up your body, usually the hips and glutes.
The fix is building strong supporting muscles/tendons, not quitting the sport.
Written by your favorite run coach, Jonathan Fors
"I used to run when I was younger. Then I got injured, so I stopped." I hear some version of that most weeks, and there's almost always a knee involved in the story.
However, running didn’t cause it. At least not the way people assume.
What people actually mean when they say they “got injured”, or have “knee pain”, is usually one of two things:
Bursitis is when the “bursa” (a small fluid-filled sac meant to soften impact and reduce friction of joint movement) in your knees becomes inflamed. Generally happens from doing more exercise than your body can support at a given time.
Osteoarthritis is when the cartilage (a smooth surface meant to protect your bones from grinding directly on top of each other when bending joints) wears down over time. There are many reasons for this, but old age, poor nutrition, or genetics are common causes.
So how is this related to running? Let’s take a look.
📚 The research
The research here is unusually clean. Running does not cause osteoarthritis and like mentioned above, people who already have knee osteoarthritis, running may even improve knee health.
One study found running has no effect on cartilage thickness or volume at all. Another study did find some changes in runners’ cartilage after a full several-month-long marathon training block, but not enough to be considered a clinical issue.
So if running is good for you, why do knees hurt?
Because the body is one large interconnected system, and knee pain is only a symptom (not cause) of a larger problem.
Muscles don't work in isolation.
Weakness in one place gets compensated for somewhere else down the chain that is a human body.
If your pelvis can’t stay straight (many have it rotated slightly forward or backward called ante- and retroversion) that’ll rotate the femur inward, which in turn changes how the knee absorbs impact. Then repeat that over 20,000 steps and suddenly you’ve got a real problem.
Ante- and retroversion of the pelvis is often caused by three things:
Tight or inflexible hip flexors which quite literally pull your pelvis forward, causing the anteversion.
General muscle imbalances, for example weak core musculature can cause the hip flexors and lower back muscles to pull harder than the core muscles can compensate for. Other common muscle causes are weak glute medius and tight quads.
Overweight or pregnant people often experience a forward tilt in the pelvis. Literally due to the extra weight a person carries in the front.
So this is why "runner's knee" often traces back to problems further up the chain rather than something being wrong with the knee itself.
What most people forget - your body adapts
Your body adapts to what you ask of it most.
Meaning if you run twice a week and do nothing for your hips, glutes or core, running stays a foreign activity to a body that spends the rest of its week not running.
And looking at the research, the numbers align perfectly.
Less experienced runners get hurt at higher rates than experienced ones, 50–75% of running injuries are overuse, and the single strongest lever on injury rates is simply weekly mileage; too much of it, too soon.
That doesn’t mean your body shouldn’t run, it simply means you’re asking it to do a completely foreign activity while lacking preparation.
Which is why personally I don't accept "I got injured at 25, so running isn't for me" from someone who's now 45.
Lifting heavy weights consistently increases bone density. Muscles respond to overload.
This holds true for people of all ages. So an old injury tells you where to be careful, not what you can or cannot rebuild.
We're the hunter gatherers that could stay on our feet all day. The knees are fine.
So if your knee hurts, don't take it as a career-ending decision.
Take it as a message about what needs to be improved. Build the hips and glutes, add volume slower than feels necessary, and let your body catch up to your ambition.
And if it doesn't settle with reduced load, see a clinician — the knee is a crowded neighbourhood, and guessing isn't coaching.
And if you ever need a hand, I’d love to work with you via group or one-on-one coaching.