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How To Use The Single Leg Squat As A Test To Pinpoint Weaknesses

Written by: Nick Jack
Category: 2014
on 03 October 2017
Hits: 31157

Without a doubt the single leg squat would be my number one choice for building strength and power for people playing sports. This one movement does so many great things for your body it is incredible. The best part is that it shares the exact timings with other joints and muscles in activities we use in everyday life. Meaning that if you improve this at the fundamental level you can also enhance these other activities too! As much as it is a great exercise, it is a very useful assessment tool we use extensively in our rehabilitation programs for all types of injuries from knee injuries like ACL tears, to lower back injuries like bulging discs. This one movement can very easily reveal stability and mobility weaknesses in your body. Where you do look? And more importantly what are you looking for? In this article I am going to answer these questions and show you how to use this movement to find energy leaks that cause pain or hinder sporting performance.

Why Is The Single Leg Squat So Good As A Test?


I have covered the single leg squat many times before as an exercise, and you can read more about this in our article Why The Single Leg Squat Is The Best Exercise For Knee Pain

But the simple answer to this question of why it is a good test is; it provides so much information about where potential leaks either in the form of stability or mobility are hiding.

But the key is you have to know what you are looking for. There are so many diagnostic tests that are used these days to assess injuries and painful conditions, and many health therapists love to put labels on things and give it a name. The big problem with today's medical world is that they look at the human body as separate parts and very closely at the area in pain, trying to isolate the tiniest part of our body and tell us we need to "fix" this as it is broken. Being ignorant to the fact that we don't move like that at all. We move with many parts all being combined in perfect sequences and timing that are all being coordinated by the brain. Just fixing or replacing a part, without looking at the role of the brain coordinating the tasks of movement is a waste of time. For even if you fixed the part, you have not addressed the more important questions of:

  1. How the part is used?
  2. Why is it in pain in the first place?

The second question of WHY is significant for the answer to this reveals what you need to do to restore function and remove pain.

In ALL cases of injury where it is not caused from a traumatic accident, the real problem is with how your body moves meaning you won't find the answer to your problem in an x-ray, MRI, or even from an examination lying on a table. You will only find the true mechanism behind the injury when you move. A great analogy to help you understand this concept is to think of a computer and how it operates.

There are both hardware and software components to a computer. If you had a problem with the internet or a particular app, there is no use replacing any of your hardware for it is a software problem. When it comes to the body it is very similar, (although the human body is a much more sophisticated computer than anything that exists). But if we stick with this analogy to help explain the concept of movement. The hardware is our bones, muscles, ligaments, tendons etc. The software is the motor programs that coordinates all these pieces of hardware.

Motor programs are ways the brain stores information about movement, and these are stored in the spinal cord as engrams. From picking up a pen off the floor, to riding a bike or throwing a ball, your brain develops a motor program that allows you to do this activity again without having to relearn all the mechanics involved. This way the brain can save storage space and energy and avoid the time consuming task of trying to put together all the individual parts of the movement each time you want to do that activity. Gray Cook talks about this a lot in his books "Movement" and "Athletic Body In Balance" and I think this is a great way to get your head around the way we move.

If you have ever played golf before and someone tries to give you a heap of tips, and your head is spinning trying to remember to do this, do that, and all that happens is you hit the ball worse than ever before!. This is because you are trying to apply a parts process to a single motor program that runs efficiently. Golf pros who teach kids, just give them the instruction to hit the ball as hard as they can. They sometimes use hockey sticks like Happy Gilmore, for they know the explosive swing and rotation will be most efficient with this cue and the body will smooth out the swing better than any technical tip that will make the kid freeze and lose timing.

We call this "paralysis by analysis"

Imagine trying to think about every muscle you need to use one by one in the task of picking up a pen off the floor? You would be exhausted if you had to move like this all the time.

The more a motor program is used the more efficient it becomes. But this is where it gets interesting. For the brain does not question if it is good or if it is bad, it only wants to perform the movement in the most efficient way it can using what it has learned. The old saying practice makes perfect is not true. "Only Perfect practice makes perfect". When it comes to the single leg squat, this is a motor program we use everyday. Whether you are an athlete, or 80 years of age, we all use this motor program for it shares the timing of walking, running, jumping and many of the very important tasks we need to do just to live our lives.

This is why it is so good for an assessment tool for it covers the needs of everyone.

What Do You Look For?

Well now we know why we use the single leg squat, what is it exactly that we are looking for? Watch the video below as I take you through a detailed look at the single leg squat and all the things that it can influence.


This is a quick summary of all the things that must happen simultaneously for this movement to be completed correctly.

  1. Foot must provide stability
  2. Ankle must provide mobility
  3. Knee must provide stability
  4. Hips must provide mobility
  5. Glutes must activate to ensure correct alignment of the lower limb
  6. Thoracic spine must remain in extension
  7. Brain must coordinate perfect timing of all these muscles and joints

When assessing this movement we start at the ground and work our way up, looking for clues as to where joints are not functioning correctly. What you will see is that every second joint needs mobility, and the other joints need the exact opposite being stability. In nearly every case of injury the joints needing stability are compromised, and forced into excessive movement due to a loss of mobility at the joints demanding this ability. This information is crucial to know in determining what course of action you may need to take, or what to investigate further when you see dysfunctional movement or pain.

Now you may think I am contradicting myself by saying look closely at specific joints. But the important thing is I must look at these joints WHILE YOU PERFORM THE MOVEMENT. If I only look at them while you are lying on a massage table or the floor I will not get the true answer to what is going on. This is where I see people have great flexibility on the floor, but extremely stiff the minute they stand up and try to move. The reason for this is a lack stability, not a flexibility problem as it appears. The body is forced to find an alternative method to stabilize itself, and it uses stiffness to protect damage to the joints. Using methods to loosen someone who is already unstable is like taking the wheel nuts off the wheels of your car and expecting the car to drive well!

This is why so many injury programs do not work and give people temporary relief. For they are missing the bigger problem that is only found when you move. What we have to do is look at the parts and then at the very end put it all back together.

Let's take a look at each joint and explain what to look for.

1: Foot (needs stability)


The feet have a tendency to being lazy, and easily losing strength and motor control. From poor footwear, to sitting too much, and even the lack of barefoot walking, the feet need exercises to make them stronger and more stable. If there is any weakness at the feet ALL joints above will be forced into poor alignment and begin compensating to make up for the loss of stability. The videos shown above provide examples of several exercises we use to help improve foot stability and big toe alignment needed to execute a perfect single leg squat. In the single leg squat you will only see the mistakes if you perform the exercise in bare feet.

If there is a problem here you will see a few things:

  1. The foot move into excessive pronation very early in the movement.
  2. The big toe lift off the floor.
  3. The entire body lose balance and either fall inwards or bend at the hips and fall outwards.

To correct foot problems you will need to strengthen the lazy feet which will take considerable time. Ideas on how you to do this are in the videos below.

Articles to read with more detail about foot stability.

  1. How To Improve The Ability To Walk
  2. Why the big toe is so important to joint stability
  3. Improve Foot Stability Using The Sensa Mat

People with lazy feet often feel the Sensa Mat hurts a lot, and will often suffer with injuries like plantar fasciitis, shin splints or achilles tendon strains. The benefit of the sensa mat for correcting this is immense and I cannot overstate how good this is. A tool every person should be using in their training.

2. Ankle (needs mobility)

The ankle tends to develop stiffness very easily and needs more focus on mobility and flexibility. It is a joint that is designed to move in 360 degrees and in combination with the hips provides all of the multi directional movements we need to do. Previous injury to wearing high heels and poor training technique all contribute to ankles becoming stiff. But remember if the feet were weak to begin with, the ankles are forced to become stiff to prevent the excessive "rolling in" of the feet. This is why it is not just as easy as doing some calf stretches or getting a massage. You have to teach the body the new way to move with the ankle within the squat itself.

The angle of flexion at the ankle needed to execute a single leg squat with full depth, but maintain good postural alignment is significant.

If you cannot achieve this it will do two things.

  1. Stop you going lower and achieving good range of movement, consequently weakening your leg muscles.
  2. Force the body to compensate and find another way to get more depth. This is often seen when someone lifts their heel and stand on their toes which in turn creates knee pain. The other compensation is flexing too much at the lumbar spine which eventually leads to lower back pain.

What you are looking for with the ankle is to see if you can achieve full range of movement.

To correct ankle mobility problems you will need to spend a lot of time working on mobility drills and also simple single leg stability drills where the ankle and feet try to work as a team. As opposed to the feet that needed strengthening the ankle needs the exact opposite. Below are some ideas of how you might do this.


Article to read with more detail on ankles - Why Poor Ankle Mobility Can Cause A Chain Reaction Of Pain

3. Knee (needs stability)

Out of all the joints the knee is the one with very little influence over what happens with movement. What do I mean by this? Well, all of the problems found at the knee are 99% of the time due to a problem at the feet, ankle or hips. Poor alignment from the feet rolling in, or the hips internally rotating cause many of the common knee injuries like Patella Tracking, ACL tears, ITB friction etc. The knee itself is not actually the problem!

What you are looking at here is to see two things.

  1. If the knee is aligned from a front on position with a line dissecting between the second toe, knee and hip.
  2. If the knee is able to go over the toes from a side on position without the heel lifting off the floor.

The VMO muscle which is always a source of discussion with knee injuries and is a known weak muscle with all knee problems. However it is very much dependent on the joints above and below in order to work as it is designed. You can isolate the VMO with endless exercises, but they are a complete waste of time if you do not teach your body how to strengthen this within a movement pattern like a lunge or squat. Because the VMO is dependent on the hip and ankle providing the alignment to begin with, it has no influence over the movement or mechanism causing your pain. It must work in tandem with the other joints and muscles in order to do it's job.


The exercises seen in the videos above are excellent examples of the VMO at work with the feet and hip to create the perfect foot, knee, and hip alignment. These are regressions of the single leg squat to assist the person in learning how to do this without the complication of stability getting in the way.

Read our article How to isolate the VMO within an integrated movement for more detail on these exercises.

There is obviously a ton of other exercises I would need to use for knee pain, and to prevent this article going for too long I have not included them all. If you do have knee pain and would like to see what else I would use you will see this is covered in great detail in our advanced Knee Pain Program with video and PDF report you can get by going to our online shop. Click here to see more.

Other articles to read with additional information regarding stabilizing of the knee are shown below.

Articles to read more about Knee Stability are:

  1. Weak VMO How To Strengthen In 5 Steps
  2. How to correct ITB friction syndrome knee pain

4: Hips (needs mobility)

This joint is often the cause of many problems to the knee and the lower back. The hips have a tendency towards stiffness from sedentary jobs making us sit all day, poor training techniques and general poor posture. And also acts as a compensatory stabilizer due to weakness from other areas such as the inner unit abdominal muscles. As a result the hips benefit greatly from flexibility and mobility work. But once again just doing stretches on the floor, without teaching the body how to use this mobility in a movement pattern is a waste of time.

What to look for is 2 things:

  1. First in a front on position look to see if the thigh bone (femur) rolls in early in the movement as pictured above. If this goes in first, and the feet are still stable and have not moved you can pinpoint a problem being driven by both tight hips and weak glutes.
  2. Second from a side on position look to see how much their butt moves backward, known as hip hinge. This is linked to the next joint very closely which you will see why shortly.

The glutes are pivotal to the single leg squat as they are the biggest muscles you have and the engine room to your lower limbs. When this exercises is done well, there is no exercise that can strengthen your butt better. They are designed to provide hip extension when we walk, run and jump, and also when we lift heavy objects off the ground, but at the same time they act as a gross stabilizer by providing external rotation of the hip when we stand on one leg.

The weaker the glutes get, the more dominant the hips become, and the more compensation that is created that ends up fuelling a chain reaction of problems both up to the lower back and down to the knee!

To correct this there are many things you will need to do. I suggest reading the 2 articles below that explain more.

  1. Article: Are Your Tight Hips The Cause Of Knee & Lower Back Pain
  2. Article: How To Strengthen Your Glutes

Also below are 2 videos that give you some good information about this and some hip mobility drill to try.


5: Lumbar Spine (needs stability)

The lumbar spine needs to be held very stable at all times to prevent unwanted flexion or extension. If stability is compromised at this joint potential injury to the spine is increased! This is why many programs focus on the "core" to improve stability. Unfortunately many of these so called "core" programs contribute to the problem, instead of correcting and really forget to look at the hips and the thoracic spine (next) as the real reason behind losing stability in the first place. Also the "Pistol Squat" is an exercise we would avoid as this really causes a lot of damage to the lumbar spine to majority of people.

Watch the video below to see why.


What to look for if stability of this area is lost is very difficult to see with your eyes. For all the work at this level is done by muscles that do not attach to any bones that move us. These deep abdominal muscles are centred around the spine and cannot move you, other than seeing a slight abdominal tension prior to moving. These muscles are known as "feed-forward" muscles, meaning they are designed to work prior to movement to ensure the spine is stable. A bit like making sure the crane is bolted to the ground before you try to lift heavy shipping containers, so the crane does not topple over. Often with back pain sufferers these muscles are very lazy and weak, and they either forget to switch on at all or come on too late exposing your spine to problems. The muscles that take over the work are usually the hips but also other muscles more designed to move you and not stabilize.

To correct this you will need to work on abdominal control and how to create pressure with your internal abdominal muscles. Using exercises that force reflex timing is critical here, which is why planks and crunches are not useful for there is no reflex at all.

Below is a great article to read about how to do this.

Article: Stability Training What Is It Really & How To Do It Correctly

6: Thoracic Spine (needs mobility)

This is an area we often consider with shoulder and neck pain but many people miss when it comes to leg injuries. Now I know you are thinking what the hell has this got to do with my sore knee? If the body loses mobility here it will force the chain reaction of poor posture onto the rest of the kinetic chain. Poor mobility at the thoracic spine is where you see a hunched posture, known as Kyphosis, usually caused from sitting and poor training techniques that makes it near impossible to get optimal alignment and hip movement. All of your other joints may have been fine, but now they are going to pay a big price due to your poor positioning.

What to look for if they do not have adequate thoracic mobility is if during a single leg squat the person is falling forward and their shoulders are hunched right up as seen in the picture on the right above. You will still need to test this to be sure but you will see a hunched posture adopted the more challenged they become. And as mentioned many times already this leads to a series of compensations at all the other joints.

This joint needs to provide mobility in both extension and rotation so you will need exercises that achieve both. Below is a great video to watch about how to do this with 6 drills you can try.


7: Brain & Coordination

Last but not least we cannot forget the brain. The most important factor to consider and the one thing that drives all movement. You could actually find that all of these joints with the corrective exercises and drills are very good and there is nothing wrong with them! The problem is that you just do not know how to squat, which is a brain and coordination problem. You will see this very clearly with kids. There is no tight or stiff areas at the ankles, hips or thoracic spine, but their movement is still terrible and appears stiff. There is all types of compensation taking place due to lack of coordination and stability. The body needs to create stiffness to counter the lack of coordination and stability and protect itself from injury.

To train the brain to improve coordination and timing the movement must be complex. For example a golf swing, or in the case of a gym exercise the single leg squat. You cannot use isolated exercises that require little brain involvement or coordination and expect the brain to change anything. You have to place the brain in the situation you want to improve and provide it with tools and methods to assist it in the learning phase. Using a stick, heel plates, TRX cables, tubing etc all are great ways to assist the stability and educate the brain on how to create better motor programs.

Below are some exercise examples of regressions of the single leg squat that can allow you to learn this movement without needing massive levels of strength. 


Using a leg press with one leg is not a great tool to use by the way. The machine is doing so much or your stability work, the brain and stabilizers are taught to no longer activate. Sure you are adding muscle but at the expense of your stability and coordination! And if you have learned anything you will know that this is corrupting your software program with a virus and only bad things will happen as a result. Always remember Movement Not Muscles!

We must force our brain to continually raise the bar of it's ability to learn. It will only change as much as the level of difficulty it faces.

FREE Report with Additional Exercises To Help You

We have covered a lot of ground and there is many things I have skimmed over. So to help you out and ensure you have all the tools you need there is 2 great reports I suggest to get a copy of below by clicking on the images.



Wow, we covered a lot of stuff in this article and I have tried my best to provide you with as many ideas on how to go about improving your ability to move. Using this exercise to pinpoint weaknesses for both injury management or performance enhancing is invaluable. I hope this article helps you to get a clearer picture of what you need to look with a single leg squat and how it can make a massive difference to your not just your training but also your life.

For always remember this:

  • If you want to be good at sports you must move well.
  • If you want to get out of pain you must move well.
  • If you want to avoid falling and be able to do daily activities with ease you must move well.

And in all cases these activities are performed standing up and will require you to stand on one leg. This one exercise can do so much, and if you ask any of our trainers they will tell you that if someone can perform a great single leg squat there is a good chance they can do almost any exercise! Spend the time to become great at this exercise it is well worth it.

For more ideas and information on specific topics I may not have covered in detail be sure to check out our INDEX PAGE on the website that has over 300 of our best articles. These are all sorted into categories for quick reference so you can find what you are after more easily. You can also subscribe to our FREE fortnightly newsletter by clicking here.

If you do need specific help with your exercise program please feel free to reach out to me for help and we can set you up with your individualised program.

About The Author

Nick Jack is owner of No Regrets Personal Training and has over 15 years’ experience as a qualified Personal Trainer, Level 2 Rehabilitation trainer, CHEK practitioner, and Level 2 Sports conditioning Coach. Based in Melbourne Australia he specialises in providing solutions to injury and health problems for people of all ages using the latest methods of assessing movement and corrective exercise.


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