You squatted 315 last week and the knees stayed out. You went for 335 today and the knees dove in on the way up. You've been told to "push your knees out" about a hundred times. You push your knees out. They still cave. The cue isn't the problem — or rather, it's not addressing the actual problem.

Knee cave is one of those faults that looks like one thing but has four or five different causes. The fix depends entirely on which one is yours. Doing hip circle warm-ups when the real issue is load management doesn't help. Neither does just telling yourself to push harder on a cue that your nervous system isn't executing correctly under load.

What Knee Cave Actually Is

Two terms get used interchangeably, but they're different problems.

Static valgus collapse: The knee tracks inward throughout the squat — from setup through descent and ascent. This is usually an anatomy or mobility issue. The hip doesn't have the external rotation available to keep the knee tracking out.

Dynamic valgus: The knee tracks fine on the way down, then caves inward at the start of the ascent — typically at or just above parallel. This is what most lifters mean when they say they have a knee cave problem. The valgus is dynamic — it appears under load, at the moment of peak demand.

Dynamic valgus at the sticking point is a force production problem. The hip abductors and external rotators can't generate enough force to maintain knee position when the load peaks. The knee collapses inward as the path of least resistance. It is not, by itself, a knee problem — the knee is following the hip's failure, not causing it.

Why It Happens: The Four Causes

1. Weak glute medius and hip external rotators

The glute medius is the primary abductor of the hip. It's supposed to fire hard during the ascent to keep the femur externally rotated and the knee tracking over the toe. If the glute med is significantly weaker than the adductors and internal rotators — which it often is in people who sit for most of the day — it loses the tug-of-war at the moment of peak demand. The knee caves.

This is the most common cause for beginner and intermediate lifters. Most people haven't trained hip abduction directly. The glutes get stronger from squatting, but the glute med often lags behind.

2. Poor motor pattern — the glutes are there but aren't firing

Some lifters have adequate glute strength in isolated tests but their nervous system doesn't recruit those muscles properly during a loaded squat. This is especially common in lifters who started training by just loading weight up without a lot of technical coaching. The movement pattern got ingrained before the musculature was properly wired into it.

These lifters will do well on side-lying clamshells. They can push their knee out with a band at light weight. Under 80%+ of their max, the same muscles stop showing up. This is a motor pattern problem, not purely a strength problem.

3. Load too heavy for current technique

This one is overlooked because no one wants to hear it. If your technique at 80% is clean and your technique at 90% falls apart, you might not have a fundamental movement dysfunction — you might just be lifting too heavy for where your technique currently is. The load is outpacing the motor pattern's ability to execute.

A useful test: drop to 60% of your max and squat. If the knees stay out perfectly, the cave is load-dependent. The fix is volume at technical weights, not targeted accessory work.

4. Hip mobility — not enough external rotation

If your stance is wider than your hip mobility supports, the femur can't externally rotate enough to keep the knee out. The body finds the range of motion somewhere else — usually by internally rotating the femur, which pulls the knee in. Widening your stance without the mobility to match is a common error when lifters copy a wide squat stance they saw someone else use.

This shows up as cave on the descent as well as the ascent. If your knees track inward on the way down, it's more likely a mobility/stance mismatch than a strength problem.

How to Diagnose Which One Is Yours

The Drills That Actually Fix It

Drill 1: Banded box squat (motor pattern + strength)

Band above the knees, sit back to a box at or just above parallel. The box eliminates the stretch reflex — you have to drive up from a dead stop, which is exactly when cave typically happens. 3 sets of 8–10 reps at 50–60% of your max squat. The goal is to feel the glutes actively pushing the knees out against the band throughout the full ascent. Don't use a band so heavy that you're just fighting it — use one that provides noticeable resistance without overwhelming you.

Drill 2: Lateral band walks

Band above the knees or at the ankles. Step out and back 15 steps each direction in a quarter-squat position. Keep the toes forward and resist the temptation to let the stepping foot turn out. The goal is strict glute med activation throughout — you should feel it burning by rep 10–12. Two sets before squatting as part of warm-up.

Don't treat this as a throwaway warm-up. Move slowly, maintain hip position, and feel the target muscle. Rushing through 20 fast steps teaches you nothing.

Drill 3: Goblet squat with pause at bottom

Hold a kettlebell or dumbbell at chest height — 20–35 lbs is enough. Squat to depth and pause for 3 seconds. At the bottom, actively push your knees out with your elbows against the insides of your thighs. Then drive up maintaining that knee position. The pause forces you to re-establish position without momentum. Do 3 sets of 5 reps. This is corrective, not conditioning — keep the weight light enough that your form is flawless every rep.

Drill 4: Single-leg glute bridge

Lie on your back, one foot flat on the floor, other leg extended. Drive the hips up by squeezing the glute of the working leg. Hold 2 seconds at the top. The single-leg version exposes left-right asymmetry — many lifters have one side significantly weaker, and the cave always shows up on the weaker side first under load. 3 sets of 10 per side.

Strength Problem or Technique Problem?

Here's how to tell: if the same fault shows up consistently across all loads — even light sets — it's a technique or mobility problem. The pattern is ingrained. Cueing and motor pattern work is the fix.

If the cave only appears when you get near your max, and your technique at 75% is solid, the issue is that the load is exceeding your strength at a specific position. The fix is more volume at 75–85%, not accessory work. You need to make your technically-sound position stronger — not re-learn the pattern.

Both problems respond to the same accessory work but for different reasons. The distinction matters because one means spending 2–3 months doing dedicated technique and accessory work before pushing weights up again. The other means you're essentially fine — just train more volume at submaximal loads and let strength catch up to technique.

If you can squat 225 with perfect knee tracking but 275 caves every time, you don't have a technique problem. You have a 275 problem. Train more at 225–245 and the 275 takes care of itself.

One Thing That Doesn't Work

Just cueing "knees out" at heavy loads without any structural change. The cue works when the underlying musculature can respond to it. Under near-maximal loads, if the glute med and external rotators can't generate enough force, telling yourself to push your knees out does nothing except give you something to feel bad about after the set. Fix the strength first, use the cue second.

Video your squat from the front at multiple loads. The frame where the cave starts — descent or ascent, and at which load percentage — tells you more than any feel-based self-assessment. Most lifters are surprised by how early their cave actually begins when they watch the footage.