Deep squats, full squats, below parallel squats, “ass-to-grass” squats, whatever you want to call them – This is probably the most talked about lift in strength training.
There are lots of opinions when it comes to squat depth. Some say that squatting as deep as possible is the only way to lift. Others think that it will screw up your knees. So, what does the science say?
Here’s what you need to know.
Deeper is better
The squat is a compound, full-body exercise that engages most muscles of the lower body. For that reason it’s widely considered to be fundamental strength movement, that much is clear. However, wide-ranging form in the gym has led to some confusion when it comes to safety.
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For example, a simple change in foot placement, barbell placement, or squat depth have huge consequences on training outcomes. A recent study found that shallow squats (about 60° knee angle) improved lower-body strength and vertical jump performance, but deep squats (below 90° knee angle) were MORE effective, promoting greater muscle mass and strength development (Reference 1).
That’s an important lesson for athletes to consider – You might be able to lift more right now by cutting your squat depth, but science suggests that you’ll be less muscular and strong overall.
What’s happening in your knee when you squat?
There are clear benefits to squatting deeper and making the lift harder, but, there’s also the ever-present safety question.
The knee joint accepts both shear and compressive forces when loaded during a squat. Ligaments (such as the ACL and PCL) stabilize the joint by regulating the shear or opposing forces. Cartilage absorbs the compressive force and stabilizes the interaction between your tibia and femur. These shear and compressive forces are typically inversely related and can be both helpful and harmful.
With knee flexion, shear forces decrease and the compressive forces increase. What this means is that stress to your ACL and PCL does not go up and you sink deeper in the squat. Increased compression around the back of the knee serves to stabilize the joint (Reference 2).
Damage to the knee only appears to occur when these compressive forces become excessive and surpass the normal capacity of the cartilage, which doesn’t appear to occur in injury free people (Reference 3).
What if you are injured?
While deep squats safe for most people, injuries require special consideration.
Sometimes it’s necessary to refrain from squatting deeper than about 60 degrees due to pain. That’s the point in the range of motion where forces on the front of your knee – around the patellofemoral joint – are at their highest.
You should also limit squat depth in the case of dysfunctional movement patterns or flexibility/mobility limitations. A great example is ankle mobility. Impaired motion at the ankle can lead to valgus, or caving knees. This is bad because it causes an uneven distribution of forces within the knee, increasing injury risk.
When in doubt, break out the squat box and only lower the height when position improves. Do that and you won’t have to worry about busting any knees.
Sore knees? Get on the box.
Take home points
Bottom line, here’s what you need to know:
- Deep squats result in greater activation of lower-body musculature compared to shallow squats.
Squatting past parallel does not result in greater shear forces, which means ACL and PCL stress does not increase past parallel.
- Deep squats increase compressive forces, which stresses the cartilage of the tibia and femur. However, recent data suggests that this cartilage is capable of enduring the magnitude of compressive forces (in injury free individuals).
- Deep squats are safe for individuals without any contraindications, assuming they are performed at a load and velocity consistent with their ability to maintain symmetry and position.
Under the supervision of a qualified professional, healthy athletes can squat deep without any concern over knee injury.
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