Are squats bad
for your knees?

For healthy knees under sensible load: no, and the evidence on that is reasonably strong. The two beliefs that say otherwise — that deep squats grind your cartilage, and that your knees must never pass your toes — are both traceable, and both weaker than their confidence suggests. But "squats are safe" is not the same as "squats are safe for everyone right now", so this page does both halves.

The deep squat question

A 2024 scoping review examined what deep squatting does to knee joint structures. Of 15 included studies, 13 affirmed the safety of deep squatting in healthy people, with no elevated injury risk. Two suggested a plausible adverse association, neither conclusively causal.¹

Two mechanisms in that review are worth knowing, because they invert the intuition:

• Cartilage adapts by thickening. Loading it appears to be a stimulus it responds to constructively, in the same general way bone and tendon respond to load — not a withdrawal from a finite account.
• Contact area grows with depth. As knee flexion increases past about 90°, patellofemoral contact area increases. The same force distributed over more surface is less pressure, not more. The deepest part of the squat is not the part where the joint is most concentrated.

On patellofemoral pain specifically, a systematic review found mixed but broadly reassuring evidence: squatting with sound form and appropriate load is not inherently a cause of patellofemoral pain syndrome.²

The 1961 problem

“Don’t let your knees go past your toes” has been repeated in gyms for over sixty years. It traces to a single paper: Karl Klein, 1961, concluding that forward knee travel in deep squats had a debilitative effect on ligamentous structures.³

Later review found no biomechanical basis for that conclusion. Forward knee travel is normal in a full squat — it is largely unavoidable if your ankles bend — and it does not appear to raise knee injury risk. The part that actually matters is what happens when you enforce the rule: restricting knee travel does not delete the load, it relocates it to the hips and lower back. You have not removed a stress, you have moved it somewhere you were not watching.

So the useful cue is not “knees behind toes”. It is knees tracking out over your mid-foot, not caving in toward each other.

Squats and knee osteoarthritis

This runs opposite to how most people assume arthritis works. Therapeutic exercise including muscle strengthening is a core recommended treatment for osteoarthritis under NICE guidance — offered to everyone with the condition, not withheld to protect the joint.⁴

There is also one striking trial. Static low-angle squatting — knees flexed to roughly 90°, held 30 minutes twice daily — in 55 people with knee osteoarthritis reduced inflammatory cytokines substantially over a year (TNF-α 22.43→14.07 pg/mL, IL-1β 80.23→43.75 pg/mL) while anti-inflammatory IL-10 rose 45.14→90.45 pg/mL, and HSS knee scores rose from 61.44 to 85.77 at two years.⁵

Read that dose again before you take anything from it. Sixty minutes of static squatting a day, supervised, for up to two years, in a specific patient population. It is a fascinating demonstration of how responsive joint tissue is to sustained loading. It is not a suggestion, and the results should not be presented — by us or anyone — as available from a few minutes of squat holds a day. If you have knee osteoarthritis, the takeaway is that a clinician-guided strengthening programme is standard care, not that you should go hold a wall sit for half an hour.

Who genuinely should be careful

The reassurance above is about healthy knees training with appropriate load. It does not extend to:

• Acute injury. A knee that is currently swollen, unstable, or newly hurt is not a knee that should be tested against a general safety review.
• Significant patellofemoral pain. Depth and load want individualising — often less depth temporarily, deliberately, with a plan to return.
• Advanced structural knee disease. Standard care includes strengthening, and what that looks like for you is a clinician’s call, not an article’s.
• Sharp, catching, or giving-way pain during a squat. That is a stop-and-get-assessed signal, not a push-through-it one.

Ordinary muscular soreness a day or two after squatting is a different animal from joint pain during the movement. The distinction is worth learning.

The practical version

• Depth is fine. Go as deep as you can with your heels down and your lower back not rounding.
• Watch for knees caving inward. Drive them out over your mid-foot.
• Do not force depth you do not have. If your ankles are the limiter, elevate your heels rather than rounding your back or pitching onto your toes.
• Progress volume gradually. Most knee grumbles from squatting are load-management stories, not technique stories.
• Knee pain that is sharp, lasting, or getting worse is a physiotherapist’s question.