How to Fix ‘Knee Cave’

Poor movement patterns (i.e. bad technique) is one of the most common reasons barbell athletes develop knee pain. Problems with knee control can sometimes be very glaring (such as an athlete who shows a significant knee collapse while performing a clean & jerk). Other times the problem can be very subtle and difficult to recognize by the untrained eye. If left untreated any amount of technique problems while lifting weights (regardless of the severity) has the ability to create frustrating and lingering knee pain that affects performance.

When we look at the knee joint, we find that it’s basically a hinge that is stuck between the ankle and hip. During most weight room movements, we want to maintain alignment of the knee between the foot and the hip.

Think about opening and closing a door. The movement of the metal hinge that connects the door to its frame operates similar to your knee joint. When you pull on the handle of the door, the hinge opens and the door opens smoothly. However, what would happen if you pulled the handle towards you while simultaneously pulling upwards as well? The door obviously wouldn’t open nearly as smooth. This is because the metal hinge joint is being pulled off axis. These same uneven forces are placed on the knee joint when it moves out of ideal alignment during a squat.

Knee Valgus

While these forces are unlikely to cause a sudden severe injury like a torn ACL while barbell training, subtle alterations in knee stability over time can have a profound effect on the smooth lining of the underside of the kneecap. If the body loses control of the knee and it starts to wobble or cave in during a lift, it causes the kneecap to rub unevenly against the femur and can lead to erosion of the smooth cartilage on the underside of the bone (similar to the athlete with EPPS compression syndrome).

How To Screen for This Problem

When I screen an athlete who has knee pain, I ask them to first perform a bodyweight squat without shoes on and with their toes straight forward. In order to perform a good full depth squat the athlete must show good ankle and hip mobility, adequate core/pelvic control, and sufficient balance.

Next I will ask the athlete to perform a single leg squat. This is often where things take a turn for the worse. There are plenty of athletes who complain of knee pain that will be able to show a good-looking bodyweight squat on two legs, however when these same athletes attempt a single leg squat, the form is horrible.

Knee Collapse

You would be surprised how many athletes I screen on a daily basis (many who would be considered elite in their respective sports) who cannot perform a simple single leg squat. Don’t believe me? Try this test yourself.

Stand on one leg with your shoe off and perform a single leg squat as deep as possible. Did your knee wobble around and cave in? Did you feel off balance in any way? Were you able to reach parallel depth (the top of your thigh below your knee)?

How to Fix The Problem?

If you were unable to control your knee during the single leg squat test, we just uncovered a possible cause of your pain: poor coordination. In order to fix this problem and decrease any pain, you need to start by improving knee stability.

The first type of exercise I want to introduce to you is called reactive neuromuscular training or RNT. First introduced by physical therapists Michael Voight and Gray Cook, RNT exercises are designed to help improve movement quality by teaching the athlete to feel for how it is moving (also known as proprioception).1

RNT Single Leg Squat

Like I mentioned earlier, many athletes can hide weak links in coordination with a double leg stance movement like the squat. For this reason, exposing these problems and then fixing on them in a single leg stance can be the most effective way to improve knee stability. For this exercise you’ll need to grab a friend and a light resistance band.

Step 1: Assume a single leg stance with your shoe off. This will allow you to concentrate on how well your foot is maintaining stability (3 points of contact aka the tripod foot).

Step 2: Place the resistance band around your leg at the height of your knee joint. Have your friend kneel beside you and pull on the band in an effort to collapse your stance knee inwards (start with a very light pull at first).

Step 3: Next, try to perform a single leg squat. In order to perform a good quality squat (with the knee in line with the foot), the body has to fight against the inwards pull of the band. Make sure to start your squat by hinging at your hips and maintain a neutral arched foot for the entire movement.

This process stimulates the body’s awareness of the knee during the squatting motion and teaches it to naturally turn on the appropriate glute muscles to keep it from collapsing.

Recommended sets/reps: 2-3 sets of 15-20 repetitions

RNT Split Squat

In order to improve knee stability in a way that carries over to other barbell training movements, you need to expose the body to different postures. Another helpful variation for improving knee stability that I like to use is the RNT split squat.

Step 1: Assume a lunge position (one leg in front of the other) with the heel of your back foot elevated off the ground. Again place a resistance band around your forward leg and have your friend pull the band inwards in an effort to collapse the knee.

Step 2: As you perform the split squat, work to maintain your knee in alignment with your foot. The resistance from the band should stimulate the lateral glutes to kick on at the appropriate time and keep the knee in a good stable position.

Recommended sets/reps: 2-3 sets of 15-20 repetitions

Balance & Reach

The next type of exercise I want to share with you is similar to the single leg touch down squat from previous articles. However, instead of squatting down and tapping the heel of your free leg next to the box, you will be simultaneously squatting and reaching out to the side.

Step 1: Stand on one leg with your shoe off.

Step 2: Start to perform a single leg squat by hinging at the hips. As you squat down, reach your free leg directly out to the side. Only reach out as far as you can while maintaining knee stability with your stance leg.

Step 3: Once you have reach the deepest single leg squat with the furthest reach with your free leg, hold this position for 3 seconds. After feeling for the glutes of your stance leg working hard, slowly return to the starting position while keeping your knee from wobbling around.

Recommended sets/reps: 2-3 sets of 10 reps with a 3 second hold at the deepest position.

Final Thoughts

The human body has an amazing ability to recognize and react to movements it identifies as familiar (also known as muscle memory).1 I find that a majority of nagging aches and pains athletes deal with aren’t due to deficits in strength, but instead the ability to turn on appropriate muscles at the right time (aka coordination). With enough repetitions, the right corrective exercises used to enhance coordination and control will eventually teach the body to react correctly in real-life situations therefore decreasing pain and future injury risk.

Until next time,

Dr. Aaron Horschig, PT, DPT, CSCS, USAW


Kevin Photo
Dr. Kevin Sonthana, PT, DPT CSCS


  1. Cook G, Burton L, Fields K. Reactive neuromuscular training for the anterior cruciate ligament-deficient knee: a case report. J Athl Train. Apr – Jun 1999; 34(2): 194-201

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11 thoughts on “How to Fix ‘Knee Cave’

  1. How could you introduce this exercises in your weightlifting routine? Or is it a specific program to do apart?

    Thanks in advance.

  2. Couple of days ago I got Knee cave while lifting weight unfortunately, I am still feeling severe pain while walking. One of my friends asked me to read this article because you have talked about the recuperating process of “Knee Cave”. Now I would like to visit website to read something more about the betting and how I could earn through it.

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