For healthy knees, no. A large 2013 review found no sign that deep squats raise the injury risk to the knee's passive tissues, like cartilage, ligaments and menisci, as long as you learn the technique and add weight gradually. That review's key force findings come from calculations and cadaver knees, not from trials that followed squatters, so the honest answer is "not bad, with conditions." If your knees already hurt, see a physical therapist before you chase depth.
The short answer: not for healthy knees, with two conditions
Deep squats aren't inherently bad for your knees. In a 2013 review of more than 164 papers, Hartmann, Wirth and Klusemann concluded that worries about cartilage wear, kneecap problems and arthritis from deep squatting were unfounded.1
Their conclusion came with two conditions, and they're the ones that matter for you:
- Technique comes first. The authors' verdict assumes you learn the squat accurately, under expert supervision.
- Load goes up gradually. Their verdict also assumes progressive training loads, not a sudden jump to heavy weights.
Pain is a separate question, covered at the end.
What does the research say about deep squats and knees?
The 2013 review set out to test a common piece of advice: that half and quarter squats are safer than deep ones. The authors searched PubMed between 2011 and early 2013.1 Their main points:
- Force behind the kneecap peaks around 90 degrees of knee bend, based on biomechanical calculations and measurements in cadaver knees. That's partway down, not at the bottom of a deep squat.
- Bending further spreads the load. What the authors call a wrapping effect improves how force is shared across the joint, and the contact area behind the kneecap keeps growing. Both lower the stress behind the kneecap.
- Knee tissues adapt. Cartilage, menisci, ligaments and bone respond to training by adapting, rather than simply wearing down.
- Partial squats may carry their own cost. The authors argue that half and quarter squats done with far heavier loads than you could take deep may favor joint wear in the knees and spine over the long run.
What it can't tell you: it's a narrative review, not a meta-analysis, and it searched a single database. The authors note that realistic estimates of the forces inside the knee during deep squats are lacking, and their key force findings come from calculations and cadaver knees. It isn't a trial that followed squatters over time and counted injuries.
Is it bad if your knees go past your toes?
Not by itself. Letting your knees travel forward shares the work between your knees and hips. In a 2003 study, Fry, Smith and Schilling had 7 weight-trained men do parallel squats with a bar equal to their body weight.2 They squatted once freely and once with a wooden barrier that stopped their knees at their toes.
| Squat style | Knee torque | Hip torque |
|---|---|---|
| Knees free to move forward | 150 N·m | 28 N·m |
| Knees blocked at the toes | 117 N·m | 303 N·m |
Blocking the knees cut knee torque by about 22%, but hip torque rose roughly tenfold, and the lifters leaned their trunks further forward. The authors concluded that sensible loading may require the knees to move slightly past the toes, because blocking them shifts force toward the hips and lower back.2
Keep the limits in mind. This was 7 men squatting a single load. Torques were estimated from video, hip torque in the free squat varied widely between lifters, and no one tracked injuries.
You'll still hear "keep your knees behind your toes." Some coaching materials teach it. The NSCA's 2012 basics manual, for example, cues lifters to keep their shins as vertical as possible in the back squat.3 The same manual also says every lifter's squat will look different depending on body type, leg length and ankle flexibility. So treat knee position as a result of your build and your depth, not a rule to force.
Why squat deep at all?
Because the extra range seems to build more muscle in some places. Two small trials compared deep and shallow squat training in men:
- Bloomquist and colleagues randomly split 17 male students into deep squats (to about 120 degrees of knee bend) or shallow squats (to 60 degrees) for 12 weeks.4 The deep group grew the front of the thigh more and improved squat-jump height more. The shallow group got much stronger at the shallow squat, about 36%, but improved only about 9% at the deep squat.
- Kubo and colleagues randomly split 17 men into full or half squats, twice a week for 10 weeks.5 Both groups grew the quadriceps about equally, by 4.9% and 4.6%. But full squats grew the glutes more (6.7% vs 2.2%) and the inner-thigh adductors more (6.2% vs 2.7%).
Both trials are small and included only men, so read them as a direction rather than a guarantee. The bigger picture points the same way: the American College of Sports Medicine's 2026 position stand, which pooled 137 systematic reviews, found that training through a full range of motion built more strength.6
How deep should you squat?
As deep as you can while your heels stay down, your back stays neutral and you stay in control. The NSCA manual treats thighs parallel to the floor as proper depth for the back squat.3 Going lower is fine if you can own the position, since the 2013 review found no added risk to healthy knees from deep squats.1
If going deeper makes your lower back round, stop just above that point and build from there. Squatting to a box or bench at a height you control, then lowering it over the weeks, is one simple way to do that. Add weight in small steps, too. Rep Labs plans your reps and weight from your training history, with warm-up sets and smart deloads, which helps with the "progressive loads" part of the review's conclusion.
5 squat technique fixes
These are coaching guidance, mostly from the NSCA manual, plus one fix that comes from the knee-position study above.
| Problem | Fix | Basis |
|---|---|---|
| 1. Knees cave inward | Push your knees out so they point the same way as your feet for the whole rep. | NSCA coaching guidance3 |
| 2. Heels lift off the floor | Keep your weight spread from the balls of your feet to your heels. Try turning your toes out slightly (anywhere up to about 30 degrees), adjusting your stance width, or using heel blocks. | NSCA lists stance width and heel blocks as normal variations3 |
| 3. Lower back rounds at the bottom | Take a big breath and brace before you go down, and breathe out near the top. Only go as deep as you can keep your spine from rounding. | NSCA: never let the spine round in a squat3 |
| 4. Hips shoot up first | Lower under control without bouncing, then drive through your feet and raise your hips and shoulders together. | NSCA coaching guidance3 |
| 5. Forcing your shins to stay vertical | Let your knees travel forward naturally as you sit down. | Blocking knee travel shifted load to the hips and lower back2 |
Fix 5 departs from the vertical-shin cue in the NSCA manual. We've gone with the measured result over the cue, but it's one small study, so let comfort and control guide you.
Squats are one part of looking after your knees. If you run as well, see Is running bad for your knees?, and if you're new to the gym, Your first 12 weeks of lifting shows where squats fit in a week.
What if your knees hurt when you squat?
Everything above is about healthy knees. The 2013 review's conclusion applies to people learning the squat with good coaching, and the NSCA manual's reassurance is explicitly about people whose knees are healthy.1,3 None of it tells you what's right for a knee that's already sore, swollen or injured.
Questions people also ask
Is it OK to squat below parallel?
For healthy knees, the evidence says yes, as long as your heels stay down, your back stays neutral and you build the weight up gradually. A 2013 review found no added injury risk to the knee's passive tissues from deep squats under those conditions. Two small trials also found deeper squats built more glute and front-thigh muscle than shallow ones.
Are half squats safer for your knees than deep squats?
Not according to the 2013 review. Its authors found that force behind the kneecap peaks around 90 degrees of knee bend, partway down, and falls as you bend further. They also argue that the much heavier loads people use for partial squats may be harder on the knees and spine over time. Partial squats have their uses, but the review gives no reason to treat them as the safer default.
Should your knees go past your toes when you squat?
They can, and for many people they need to. In a small study of 7 trained men, stopping the knees at the toes cut knee torque by about 22% but raised hip torque roughly tenfold and made the lifters lean further forward. How far your knees travel depends on your build, your ankle flexibility and how deep you go.
What should I do if my knees hurt when I squat?
Stop loading through the pain and get it checked by a physical therapist or doctor. The research on deep squats is about healthy knees, so it can't tell you what's right for a painful or injured one. A physical therapist can help you find a range and a load that suit your knee.
Sources
- Hartmann H, Wirth K, Klusemann M (2013). Analysis of the load on the knee joint and vertebral column with changes in squatting depth and weight load. Sports Med 43(10):993-1008.
- Fry AC, Smith JC, Schilling BK (2003). Effect of knee position on hip and knee torques during the barbell squat. J Strength Cond Res 17(4):629-633.
- Sands WA, Wurth JJ, Hewit JK (2012). Basics of Strength and Conditioning Manual. National Strength and Conditioning Association.
- Bloomquist K, Langberg H, Karlsen S, et al. (2013). Effect of range of motion in heavy load squatting on muscle and tendon adaptations. Eur J Appl Physiol 113(8):2133-2142.
- Kubo K, Ikebukuro T, Yata H (2019). Effects of squat training with different depths on lower limb muscle volumes. Eur J Appl Physiol 119(9):1933-1942.
- Currier BS, D'Souza AC, Singh MAF, et al. (2026). American College of Sports Medicine position stand. Resistance training prescription for muscle function, hypertrophy, and physical performance in healthy adults: an overview of reviews. Med Sci Sports Exerc 58(4):851-872.