Form Guide

How to Fix Knee Cave on Bodyweight Squats

Knee cave (also called knee valgus) is the squat equivalent of elbow flare. It looks harmless at bodyweight, but it grooves a motor pattern that wrecks knees when load is added. The mechanics are unforgiving: every time the knee tracks inside the foot, the medial collateral ligament and ACL take more stress than they should.

The fix is mostly about waking up the glute medius (the side glute) and retraining the brain to drive the knees out on every rep. Here is the step-by-step.

What knee cave actually is

In a clean squat, the kneecap tracks directly over the second or third toe through the entire range. In a cave, the knee collapses toward the midline. Three patterns are common:

• Descent cave: knees collapse on the way down. Usually a stance or mobility issue.
• Bottom cave: knees stay tracked but collapse at the deepest point. Usually weak hip external rotators.
• Ascent cave: knees collapse on the way up, especially at the "sticking point" two-thirds of the way up. Almost always weak glute medius and overactive adductors.

Identify which type you have by filming yourself from the front. The fix is similar for all three, but you will know where to focus extra attention.

Why your knees cave

Three causes account for nearly every case:

1. Weak glute medius. The side glute is the primary external rotator of the hip. If it is underdeveloped (and in most desk-bound adults it is), the adductors pull the femur inward unopposed.
2. Poor motor pattern. The brain has never been trained to drive the knees out. The fix is repetition with feedback.
3. Stance and foot pressure issues. Feet too narrow, toes pointed straight forward, or weight shifted to the inside of the foot all encourage cave.

Step by step: the fix

1. Reset your stance. Feet shoulder-width, toes turned out 5 to 15 degrees, weight spread across the whole foot. Press the outside edges of your feet into the floor before you descend.
2. Spread the floor. Without actually lifting your feet, try to push them apart. You should feel the glutes engage. This is the active cue that replaces the passive collapse pattern.
3. Add a mini-band above the knees. Loop a mini-band just above the kneecaps. Squat against the band, actively pushing out the entire time. The tactile feedback is unmistakable.
4. Drive the knees over the pinky toe. Through the entire rep, cue your knee toward the pinky toe (not the big toe). Most people undershoot when they "drive the knees out."
5. Train the glute medius. 3 sets of side-lying clamshells or banded side-steps before each squat session. Wake the muscle up so it actually fires during the squat.
6. Slow tempo squats. 3 sets of 8 squats with a 3-second descent. The slower the rep, the harder it is to hide the cave, and the more conscious control you can apply.
7. Film yourself. Set your phone on the floor in front of you. The knees do not lie when you watch the playback.

Common mistakes when fixing knee cave

1. Pushing the knees too far out (knee bow)

Why it happens: overcorrection. The lifter forces the knees so far out that they track outside the foot, which is also bad mechanics.

Fix: aim for knee directly over pinky toe. Not inside, not outside.

2. Stopping the band drills too early

Why it happens: the lifter feels the new pattern after a few sessions and assumes it is fixed.

Fix: use the band for at least 2 full weeks. Then test unbanded squats and confirm the pattern holds under fatigue. Re-introduce the band any time the cave returns.

3. Ignoring the foot

Why it happens: the lifter focuses on the knee but the weight is shifted to the inside of the foot, which mechanically drags the knee inward.

Fix: press the outside edges of the feet down. The arch should stay supported, not collapsed.

4. Adding load before the pattern is clean

Why it happens: the lifter wants to keep training heavy squats and treats form work as a separate accessory.

Fix: drop load by 30 to 50% for 2 to 3 weeks while you fix the pattern. Loaded reps with cave reinforce the bad pattern faster than form drills can fix it.

Glute medius drills that actually work

Two drills before every squat session:

• Side-lying clamshells. Lie on your side, knees bent 90 degrees, mini-band above the knees. Keep feet together and lift the top knee. 3 sets of 15 per side.
• Banded side-steps. Mini-band above the knees, half-squat position. Step sideways 10 steps each direction. 3 sets.

Both target the glute medius directly. Done before squats, they "prime" the muscle to fire during the working sets.

When to see a physiotherapist

If you have ongoing medial knee pain, a previous ACL injury, or your knees cave even with bodyweight despite a few weeks of corrective work, see a physiotherapist. There may be a mobility or anatomical factor that needs assessment before you load the squat.

Frequently asked questions

Is knee cave actually dangerous?

Yes, under load. Knee valgus stresses the MCL and ACL and is a documented risk factor for ACL tears. Even at bodyweight, repeated cave grooves a bad pattern.

Why do my knees cave only on the way up?

The glute medius fatigues or never fully activates, and the adductors pull the femur inward as you press up. Glute medius work and the spread-the-floor cue usually fix it within weeks.

Will a knee band fix knee cave permanently?

The band trains the active push-out pattern, but you need to test unbanded squats and prove the pattern holds. Use the band for 2 to 3 weeks, then as an occasional refresher.

What if only one knee caves?

Single-side cave usually means a glute medius imbalance. Train the weaker side with extra unilateral work like single-leg glute bridges and Bulgarian split squats.