Back Squat: Common Knee Mistakes, Causes, and Prevention

What should you avoid doing with your knees during a back squat?

To safeguard your knees during a back squat, avoid excessive valgus (caving in) or varus (bowing out) collapse, unnecessary forward knee travel beyond what ankle mobility allows, and hyperextension at the top of the movement, all of which can compromise joint integrity and increase injury risk.

Introduction

The back squat is a foundational exercise revered for its ability to build lower body strength, enhance athletic performance, and improve overall functional movement. However, despite its benefits, improper technique—particularly concerning knee mechanics—can lead to discomfort, acute injury, or chronic issues. Understanding what to avoid with your knees is paramount for a safe and effective squat.

The Knee Joint: A Brief Biomechanical Overview

The knee is a complex hinge joint primarily responsible for flexion and extension, with a small degree of rotation. It comprises the articulation between the femur (thigh bone), tibia (shin bone), and patella (kneecap). The patella tracks within a groove on the femur (the trochlear groove), and its proper movement is crucial for pain-free function. Ligaments (ACL, PCL, MCL, LCL) provide stability, while muscles (quadriceps, hamstrings, glutes, calves) control movement and absorb force. Optimal knee health during a squat relies on maintaining proper alignment, which minimizes undue stress on these structures.

Key Knee Mistakes to Avoid During the Back Squat

Knee Valgus Collapse (Knees Caving In)

What it is: This is arguably the most common and concerning knee error. It occurs when the knees drift inward towards the midline of the body, especially during the eccentric (lowering) phase or concentric (lifting) phase of the squat. Why it's problematic:

• Increased stress on the Medial Collateral Ligament (MCL): This ligament resists valgus forces, and repeated stress can lead to sprains.
• Patellofemoral pain: The inward collapse can cause the patella to track improperly, leading to pain around or under the kneecap.
• Increased Anterior Cruciate Ligament (ACL) risk: While multifactorial, valgus collapse is a significant risk factor for non-contact ACL injuries, particularly under load.
• Reduced power output: It indicates a loss of stability, compromising the efficiency of force transfer. Common causes:
• Weak gluteus medius and maximus: These muscles are crucial for hip abduction and external rotation, which help keep the knees aligned.
• Overactive adductors: Tight or dominant inner thigh muscles can pull the knees inward.
• Limited ankle dorsiflexion: If the ankles can't move sufficiently, the body compensates by allowing the knees to cave to maintain balance.
• Poor motor control or cueing: Lack of awareness or incorrect instructions. How to avoid it:
• "Knees out" cue: Actively think about driving your knees outwards, tracking over your mid-foot or slightly outside.
• Strengthen hip abductors and external rotators: Incorporate exercises like glute bridges with bands, clam shells, and band walks.
• Improve ankle mobility: Focus on dorsiflexion drills.
• Widen stance slightly: For some individuals, a slightly wider stance can facilitate better knee alignment.

Knee Varus Collapse (Knees Bowing Out Excessively)

What it is: Less common than valgus collapse, this occurs when the knees bow outwards excessively, beyond the natural alignment over the feet. Why it's problematic:

• Increased stress on the Lateral Collateral Ligament (LCL): While rare in squats, excessive varus can strain this ligament.
• Altered joint mechanics: Can lead to uneven loading across the knee joint.
• Suboptimal muscle recruitment: May indicate over-reliance on certain hip external rotators or an attempt to compensate for other mobility limitations. Common causes:
• Over-cueing "knees out": Taking the instruction too literally or pushing beyond the natural range.
• Specific anatomical variations: Some individuals naturally have a slight varus alignment. How to avoid it:
• Focus on neutral tracking: Aim for the knees to track directly over the second or third toe, rather than pushing them out as far as possible.
• Controlled movement: Ensure glute activation without forcing excessive external rotation.

Excessive Forward Knee Travel (Knees Beyond Toes, Unnecessarily)

What it is: While the adage "knees never past toes" is largely debunked (it's often necessary and natural for optimal depth), excessive forward knee travel refers to the knees moving significantly beyond the toes without corresponding hip hinge, leading to an overly vertical torso and quad-dominant squat. Why it's problematic:

• Increased shear forces on the knee: Emphasizes the quadriceps and places greater anterior shear stress on the knee joint and patellar tendon.
• Reduced posterior chain involvement: Limits the contribution of the powerful glutes and hamstrings.
• Balance issues: Can make it harder to maintain balance, especially with heavier loads. Common causes:
• Limited ankle dorsiflexion: The most common culprit. If the ankles can't bend enough, the knees are forced forward to achieve depth.
• Weak posterior chain: An inability to adequately hip hinge and engage the glutes/hamstrings.
• Quad dominance: Over-reliance on the quadriceps. How to avoid it:
• Prioritize the hip hinge: Initiate the squat by pushing the hips back first, as if sitting into a chair.
• Improve ankle mobility: Regular ankle dorsiflexion stretches and drills are crucial.
• Strengthen the posterior chain: Include exercises like Romanian deadlifts, good mornings, and glute-ham raises.
• Consider squat variations: High-bar squats and front squats naturally allow more forward knee travel, but it should still be controlled and proportional to hip movement. Low-bar squats encourage less.

Knee Hyperextension at the Top

What it is: This occurs at the top of the squat when the knees are "locked out" forcefully, moving beyond a straight line and into a slight backward bend. Why it's problematic:

• Increased stress on passive structures: Places undue strain on the knee joint capsule and ligaments (ACL, PCL) rather than relying on muscular control.
• Reduced muscular tension: Allows the muscles to disengage, which can be detrimental under heavy loads and doesn't promote continuous tension.
• Risk of injury: Repeated hyperextension can contribute to joint laxity over time. How to avoid it:
• Maintain a "soft" knee: At the top of the squat, fully extend your hips and stand tall, but keep a slight bend in your knees.
• Engage quadriceps and hamstrings: Actively contract the muscles around the knee to maintain stability rather than relying on passive lockout.
• Focus on controlled movement: Avoid "snapping" into the top position.

Improper Patellar Tracking

What it is: This is when the kneecap (patella) does not glide smoothly within the trochlear groove of the femur, often drifting laterally (outward). This is frequently a result of other issues like valgus collapse or muscle imbalances. Why it's problematic:

• Patellofemoral pain syndrome (PFP): The most common consequence, leading to pain around or behind the kneecap.
• Cartilage wear: Chronic improper tracking can lead to erosion of the cartilage surfaces. Common causes:
• Muscle imbalances: Weakness in the vastus medialis obliquus (VMO) relative to the vastus lateralis, or general hip muscle weakness (glutes).
• Excessive valgus collapse: A primary driver of lateral patellar tracking.
• Tight IT band or lateral retinaculum: Can pull the patella outward. How to avoid it:
• Address underlying issues: Correct valgus collapse and improve hip strength.
• Target VMO strengthening: While difficult to isolate, exercises that involve terminal knee extension with external rotation may help.
• Ensure knee tracks over mid-foot: This is the primary visual cue for proper patellar alignment during the squat.

General Principles for Knee Health in Squatting

• Prioritize Mobility: Ensure adequate ankle dorsiflexion and hip mobility (internal and external rotation) to allow for proper depth and alignment.
• Strengthen Supporting Muscles: Focus on strengthening the glutes (maximus, medius, minimus), hamstrings, core, and hip adductors. A balanced approach is key.
• Warm-Up Thoroughly: Prepare your joints and muscles with dynamic stretches and light cardio before squatting.
• Progress Gradually: Do not add weight or depth until your form is consistently sound. Master bodyweight and goblet squats before moving to heavy back squats.
• Listen to Your Body: Pain is a warning sign. If you experience knee pain, stop, reassess your form, reduce the load, or consult a qualified professional.
• Seek Expert Guidance: A qualified coach or physical therapist can provide personalized feedback and correct subtle technique flaws.

Conclusion

The back squat is an invaluable exercise, but its benefits are maximized only when performed with meticulous attention to form, especially concerning knee mechanics. By actively avoiding knee valgus/varus collapse, unnecessary excessive forward knee travel, and hyperextension, you can significantly reduce the risk of injury, optimize muscle activation, and ensure the longevity of your knee health. Remember, proper technique isn't just about lifting more weight; it's about moving efficiently, safely, and sustainably.