Knee pain during squats is rarely about the squat itself. It’s almost always about how you’re squatting, and small adjustments to your stance, depth, and ankle mobility can dramatically change the forces acting on your knee joint. Here’s what actually causes that pain and how to fix it.
Why Squats Hurt Your Knees
The kneecap sits in a groove on the front of your thighbone, and every time you bend your knee under load, the cartilage behind the kneecap gets compressed. This is called patellofemoral joint stress, and it increases sharply as you squat deeper. A study in Applied Sciences measured this directly: going from a moderate squat depth (about 75 degrees of knee bend) to a deep squat (about 100 degrees) increased kneecap compression by 62%. At the deeper position, back squats produced peak stress of roughly 21.5 MPa compared to 14 MPa at the shallower depth. Front squats were even higher at depth, hitting about 24.3 MPa.
That doesn’t mean deep squats are inherently bad. It means that if you already have irritated cartilage or a sensitive kneecap, depth is the single biggest lever you can pull to reduce pain. Staying at or just above parallel (roughly 90 degrees of knee bend) keeps compressive forces substantially lower than going “ass to grass.”
The Ankle Mobility Problem
Stiff ankles are one of the most overlooked causes of knee pain during squats. When your ankle can’t bend forward enough (a movement called dorsiflexion), your body compensates in ways that punish your knees.
Research in the Journal of Athletic Training classified people as having normal ankle mobility (15 degrees or more of dorsiflexion) versus limited mobility (5 degrees or less) and had them squat. The limited group achieved less knee bend and less forward ankle motion during the squat. That matters because less knee flexion actually increases the forward shearing force on your shinbone, putting more strain on the patellar tendon and the ACL. Your hamstrings, which normally help counteract that shearing force, are also less effective at smaller knee angles. So paradoxically, not bending your knees enough can hurt them more than bending them properly.
A simple test: face a wall, place your foot about 4 inches away, and try to touch your knee to the wall without lifting your heel. If you can’t do it, limited ankle mobility is likely contributing to your squat pain.
Let Your Knees Travel Forward
You’ve probably heard the cue “don’t let your knees go past your toes.” It’s one of the most persistent pieces of gym advice, and it’s largely counterproductive. A comprehensive review in the Journal of Clinical Medicine examined what actually happens when you restrict forward knee travel during squats. Yes, knee torque drops by about 28% when you keep your knees behind your toes. But here’s the tradeoff: hip torque increases by a staggering 973%. You’re not eliminating stress, you’re just dumping it onto your lower back and hips instead.
For most people, allowing the knees to naturally track forward over the toes distributes force more evenly across the joints. The key is that the movement should be controlled and that your knees track in line with your toes rather than collapsing inward.
Adjust Your Stance Width and Foot Angle
Small changes to how you set your feet can meaningfully shift where force lands on your knee. Research in BMC Sports Science found that a wider stance reduced knee adduction moments, which is the inward-collapsing force that loads the inner compartment of your knee. If you’ve been squatting with a narrow, hip-width stance and feeling medial (inner) knee pain, widening to roughly 1.5 times hip width may help.
Turning your toes out also matters. A 20-degree toe-out angle reduced peak inward knee forces compared to a toes-forward or toes-in position. The combination of a moderately wide stance with feet angled out 15 to 30 degrees is a good starting point if you’re troubleshooting knee pain. Your knees should track over your second or third toe throughout the movement.
Elevate Your Heels
If ankle stiffness is limiting your squat, heel elevation is the fastest workaround. Placing small weight plates, a wedge, or wearing squat shoes with a raised heel compensates for restricted dorsiflexion and lets you achieve better squat depth with a more upright torso. Research in Bioengineering confirmed that elevating the heels reduces the forward trunk tilt during barbell squats, which in turn reduces shear forces on the lower back.
Start with a half-inch elevation and adjust from there. Many people find that even a modest lift eliminates the compensatory patterns that were overloading their knees. This isn’t a permanent crutch. Use it while you work on improving actual ankle flexibility through stretching and mobility drills.
Managing Existing Knee Tendon Pain
If you’re dealing with patellar tendon pain (that sharp ache just below the kneecap), the worst thing you can do is stop loading entirely. Tendons need controlled stress to heal and remodel. The current rehabilitation approach uses a tiered loading strategy, starting with low-demand exercises and gradually increasing the stress on the tendon.
The Spanish squat is commonly recommended as an early-stage exercise for tendon rehab. You loop a resistance band around a sturdy post at knee height, step into the band so it sits behind your knees, and lean back while squatting. The band pulls your shins forward, which shifts load onto the tendon in a controlled way while reducing the compressive force behind the kneecap. It’s also practical because it requires nothing more than a band and something to anchor it to.
From there, progression typically moves through double-leg squats at moderate depth, then single-leg variations, then plyometric and sport-specific movements. The principle is consistent: load the tendon progressively rather than avoiding it. Pain during these exercises should stay mild and settle within 24 hours. If it’s getting worse session to session, you’ve progressed too quickly.
Putting It All Together
If squats currently hurt your knees, run through these adjustments in order:
- Check your depth. Stay at or slightly above parallel until pain-free. Deep squats increase kneecap compression by over 60% compared to moderate depth.
- Test your ankle mobility. If it’s limited, use heel elevation and begin daily calf and ankle stretching.
- Widen your stance. Move to about 1.5 times hip width with toes turned out 15 to 30 degrees.
- Let your knees travel naturally. Restricting forward knee movement dramatically increases hip and lower back stress without meaningfully protecting the knee.
- Control the descent. A 2 to 3 second lowering phase reduces the peak forces on your joints compared to dropping quickly.
Most people find that one or two of these changes eliminate their pain entirely. If you’ve made all these adjustments and still have significant discomfort, the issue is more likely structural (cartilage damage, meniscus irritation, or tendon pathology) and worth getting evaluated with imaging rather than continuing to troubleshoot form on your own.