Your Knees Are Not Tires: Exercise and Knee Arthritis
Joints aren’t parts that wear out from being used. They’re living tissue that gets worse when you stop using them.
46 TRIALS — 3,463 people with knee arthritis, pooled and ranked. Loading the joint didn’t make it worse. It made pain, stiffness and function better.
The tire model of a joint — you get so many miles, then the tread is gone — is the most common thing I have to un-teach. It leads people to protect the joint by using it less, which is precisely the thing that makes it hurt more. Three pieces of research from the last year, including one that argues against a point I’d rather make.
“Exercise wears my knee down” — myth or reality?
JOSPT, July 2025
Researchers took the question head on and reviewed what the imaging studies actually show in people who either have knee arthritis or are at risk for it. The conclusion: exercise therapy does not appear to harm cartilage structure or quality. They go further and tell clinicians to bring this up on purpose, because the fear itself is doing damage — people stop moving to protect a joint, and the joint gets worse.
Worth being precise: this says exercise doesn’t appear to hurt cartilage. It isn’t a promise that any load, at any speed, on any day, is fine. That’s a coaching problem, and it’s mine to manage.
It’s not how heavy. It’s how fast.
BMC Musculoskeletal Disorders, 2025
A network meta-analysis pooled 46 randomized trials and 3,463 people with knee arthritis and ranked the different ways of strength training against each other. The winner wasn’t the heaviest. It was high-speed resistance training — moving a moderate load with intent — which came out on top for pain, for stiffness, and for function.
The loads that worked best were moderate, not maximal. Which is the part people find hardest to believe: you don’t have to grind a heavy knee to make it better. You have to ask it to move well, repeatedly, over months.
The uncomfortable one: doing it alone works less well
Journal of Clinical Medicine, 2025
Ten randomized trials, 917 patients with knee arthritis, comparing home exercise programs against supervised ones. Both helped. But supervised training beat unsupervised home programs on both pain and disability — and supervised was the only one of the two to clear the threshold researchers use for “a difference the patient actually notices.”
The gaps were small, and the authors are careful about it: home work is still valuable, and what predicted results inside the home group was simply how often people did it. Their actual recommendation is a hybrid — supervised sessions plus homework.
Matt's take
I’ll be straight about study three: I sell supervised training, so a paper saying supervised beats going it alone is one I have an obvious interest in. Read it with that in mind. But I don’t think the finding is really about supervision. It’s about dose and progression. The home groups that did the work more often got better results, and the supervised groups just did the work more often. Someone showing up is the most reliable way anyone has found to make that happen. If you train on your own and you actually do it three days a week for three months, you will be fine.
The second study is the one that should change something this week. Speed, not weight. When I have you stand up out of a chair and drive up quickly, or push a step-up with intent instead of grinding it, that isn’t me going easy on you — that’s the version that beat everything else in 46 trials. Moderate load, moved with purpose.
If you’re at a desk all day: your knees and hips aren’t wearing out, they’re under-used. A joint gets its nutrition from being loaded and unloaded — cartilage has no blood supply of its own, so motion is how it gets fed. Ten hours in a chair is ten hours of a hip that never reaches the end of its range. That stiffness you feel standing up at 4pm is not age. Get up every hour. Five sit-to-stands, done briskly, is enough to count.
If you’re training around arthritis or a replacement: the rule I use is the 24-hour rule. Soreness in the muscle that settles by the next day means we loaded it right. Sharp pain in the joint line during the movement, or a joint that’s more swollen and stiff the next morning, means we went too far — and the answer is to adjust the range, the speed or the load, not to stop. Start where the joint is comfortable and expand outward. Warmth before, not heroics during.
If you have an inflammatory arthritis, a joint replacement, a scheduled surgery, or your doctor has given you specific restrictions, tell me and follow them — I’m a strength coach, not your physician, and I’d rather build the program around what your surgeon said than around what I assumed. If you’ve been told your knee is “bone on bone” and to stop exercising, that’s worth a second conversation with your doctor, because the current evidence points the other way.
Train this at home
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This article first ran in the Forged Home Fitness weekly newsletter. It is general fitness education, not medical advice, and does not replace your physician.
