Are Squats Bad for Your Knees? What the Research Actually Says

Are squats bad for your knees? For healthy people, the best available research says no. A narrative review of over 164 articles concluded that deep squats do not add injury risk to passive tissues like ligaments and cartilage, as long as technique is learned and loads rise gradually (Hartmann et al., 2013).

That does not mean every squat feels good for every knee. It means the blanket rule “squats ruin knees” is not what the evidence shows. This article is part of our joint-friendly lifting myth-busting guide, and it covers where the myth came from, what the biomechanics say about the kneecap, and why the knees-over-toes rule backfires.

Where did the “squats destroy your knees” myth come from?

The belief is commonly traced to early-1960s work that linked deep squatting with looser knee ligaments, often credited to Karl Klein. I have not linked that paper because I could not check its methods against a PubMed abstract, so treat the details with caution.

What I can verify is how the later literature treated the idea. The Hartmann review looked at the claim that deep flexion should be avoided to limit knee forces. It argued that this advice ignored the wrapping effect, functional adaptation and the way soft tissue at the back of the thigh and calf shares load. Its conclusion on deep squats was blunt: concerns about chondromalacia, osteoarthritis and osteochondritis from deep squats were unfounded (Hartmann et al., 2013).

An old rule, repeated by coaches and physios for decades, can feel like fact. It is still worth checking against newer data.

What happens to your kneecap in a deep squat?

The kneecap (patella) glides in a groove at the end of the thigh bone. When you bend your knee under load, the quadriceps and patellar tendon press it into that groove. That pressure is called patellofemoral stress.

According to the Hartmann review, which relied on biomechanical calculations and cadaver knee studies, the highest retropatellar compressive forces and stresses occur at about 90 degrees of knee flexion. Beyond that, the wrapping effect helps spread load, and the contact area between kneecap and thigh bone keeps growing, which lowers compressive stress (Hartmann et al., 2013). The same review notes there are no realistic force estimates beyond roughly 50 degrees in the deep squat, so this is a model-based picture, not a direct measurement inside living knees.

Does this mean deeper is always better for the knee?

No, and the research is not uniform here. A biomechanical model in experienced female lifters found peak patellofemoral joint reaction force was higher at below-parallel depth than at parallel or above, and stress rose with load at each depth (Zavala et al., 2021).

Why might these studies differ? Hartmann summarised cadaver data and calculations from many articles and considered contact area, while Zavala modelled forces and stress in a specific sample of women using knee moments and joint angles. Forces going up with depth is not the same as injury going up, because tissue adapts to load. A cautious takeaway: heavy loads at the very bottom are the demanding part, so build up to them.

Another model-based comparison found squats produced more patellofemoral stress than knee extensions at 60 to 90 degrees of flexion, but less at 0 to 30 degrees (Powers et al., 2014). That is useful if you are managing front-of-knee pain, which is covered in our guide to training around knee pain. It was a study of ten healthy people, so it informs exercise choice rather than proving harm.

Should your knees go past your toes?

You have heard “never let your knees go past your toes.” The idea is to keep the shin vertical so the knee is spared.

Fry and colleagues tested exactly that. Seven weight-trained men did parallel squats with a bodyweight load, once with knees free to travel and once with a wooden barrier stopping them at the toes. With knees free, knee torque averaged 150.1 N.m and hip torque 28.2 N.m. With the barrier, knee torque fell to 117.3 N.m but hip torque jumped to 302.7 N.m, and the trunk leaned further forward (Fry et al., 2003).

So restricting the knees did reduce knee demand, but it moved a large amount of torque to the hips, and the authors suggested to the low back as well. That is roughly a tenfold increase at the hip in this sample, although the individual results varied a lot. The authors suggested that appropriate loading may require the knees to move slightly past the toes.

A more recent review agrees. It describes the toe rule as a persistent myth from 1970s and 1980s research, notes the hip and lumbar spine take high peak torques when knee travel is deliberately limited, and concludes that for healthy trained people restricting it is likely not effective. The exception is knee rehabilitation, where a clinician may want it (Illmeier & Rechberger, 2023).

You may have seen a claim that the toe rule raises low-back stress by 1000 percent. The Fry hip torque figures are in that ballpark, but they are static torques from seven men squatting bodyweight, so I would not repeat “1000 percent” as a universal figure for spinal load.

Are deep squats better or worse than half squats for the knees?

A common alternative is to “protect” the knees with quarter or half squats. The evidence does not support that idea for long-term joint health.

Hartmann and colleagues argued that half and quarter squat training with comparatively supramaximal loads may favour degenerative changes in knee and spinal joints over time, while deep squats with learned technique and progressive loads strengthen the lower body (Hartmann et al., 2013). That is a review argument, not a long-term trial, so keep that in mind.

A direct comparison exists for muscle and tendon outcomes. In a 12-week randomised trial, 17 male students trained either deep squats (0 to 120 degrees of knee flexion) or shallow squats (0 to 60 degrees). Deep squats produced larger gains in front-thigh muscle size (4 to 7 percent more), isometric knee extension strength and squat-jump performance. Patellar tendon cross-sectional area did not differ between groups (Bloomquist et al., 2013). The sample was small and made of young men who were not necessarily trained, so apply it cautiously.

For more on depth and growth, see our article on squat depth science for hypertrophy.

Question	What the evidence says	Caution
Do deep squats damage ligaments or cartilage?	Narrative review of 164+ articles: concern unfounded	Model and cadaver based
Is the kneecap most stressed at the bottom?	Peak near 90 degrees, easing beyond	Other models show higher force at below parallel
Do knees past toes harm knees?	Blocking them raised hip torque sharply	7 men, bodyweight only
Are half squats safer?	Not clearly, and deep built more thigh muscle	One small 12-week trial

Do squats make your tendons and ligaments stronger?

Tendons respond to load, but slowly. A systematic review and meta-analysis of 61 studies (763 participants) found that mechanical loading produced moderate increases in tendon stiffness (SMD 0.74), large increases in modulus (SMD 0.82) and small increases in cross-sectional area. Resistance training with higher tendon strain produced greater gains than low-strain protocols (Lazarczuk et al., 2022).

The practical message is that tendons are not fragile things to be wrapped in cotton wool, but they do not adapt overnight. Muscles often get stronger faster than tendons can keep up, which is why jumping from nothing to heavy squats is a classic way to irritate a knee. Our article on connective tissue adaptation timelines goes deeper on this.

How to squat safely: a progression for your knees

The point is not to avoid depth. It is to earn it.

• Start with a depth you control. A goblet squat or bodyweight squat to a depth where your heels stay down and your back stays steady is a fine start.
• Fit the stance to your hips. Femur length and hip shape change what a comfortable stance looks like. Our articles on stance width and foot placement and adapting range of motion to your anthropometry cover how to test this.
• Slow the lowering phase. A 2 to 3 second descent builds control and gives you feedback about where the knee feels loaded.
• Add weight in small steps. Increase load over weeks rather than session to session, and keep most sets with 1 to 3 reps left in the tank.
• Treat lingering pain as information. A mild ache that settles within a day is different from sharp pain, swelling or pain that builds. Our leg day plan is a reasonable starting layout if you want a structure to follow.

If you want to see the difference between technique variations, our comparison of high bar and low bar squat biomechanics is a good next read, and knee sleeves versus wraps covers whether gear changes the picture.

What if you already have knee pain or osteoarthritis?

Everything above applies to healthy knees. It is not a diagnosis, and it does not tell you what to do about a painful or diagnosed knee.

Resistance training is commonly used as part of knee osteoarthritis care. A systematic review and network meta-analysis of 39 randomised trials (2,646 participants) found that all five exercise types it tested, including resistance training, improved knee osteoarthritis outcomes versus control, though most trials failed to blind participants and risk of performance bias was high (Mo et al., 2023). It does not tell us which squat depth is right for your knee.

See a doctor or physiotherapist if you have:

• Swelling that appears after training
• Locking, catching or the knee giving way
• Pain that wakes you at night or builds over several weeks
• Pain following a twisting injury or a pop

Until then, drop the load, shorten the range to where the knee is comfortable, and avoid pushing through sharp pain.

The bottom line on squats and your knees

Squats are not shown to be bad for healthy knees. The idea that depth wrecks the joint comes from old assumptions that later reviews did not support. Kneecap stress does rise with heavy loads, and there is no single perfect depth, so progress gradually. Skip the knees-over-toes rule unless a clinician has told you otherwise, and listen to persistent pain. A patient training plan and good recovery will do more for your knees than any rule about toes.