Few exercises are more loved and more hated in the same time than barbell squats. And among the many types of squats probably none is considered less controversial than deep squat – or full squat if you wish.
For a whole generation of coaches this was the very symbol of evil: knee-crushing, tendon-tearing, back-breaking villain – and pretty useless, to be sure. Squatting lower than 90-degrees angle between the shins and thighs was damned as pure heresy.
There are schools (clubs, periodicals, even whole countries) where coaches daring to transgress this holy dogma are viewed almost as child-abusers even today.
So let’s examine the arguments for and against deep squats.
The origins of “Deep-squat-is-bad” theory
In 1961, Dr. Karl Klein of University of Texas published a paper called “The deep squat exercise as utilized in weight training for athletes and its effects on the ligaments of the knee”.
In his study comparing weightlifters with a control group, Dr. Klein argued that deep squats caused loosening of the knee ligaments (specifically of the collateral and anterior cruciate ligaments) as measured by a device that he himself designed.
This led to much speculation but little serious research. Still, as there were no other scientific studies proving the theory wrong, the American Medical Association (AMA) released a position statement against the deep squat. This position statement is the source of many older coaches’ disdain for full squat.
Still, many athletes and coaches didn’t buy into the shallow-squat theory even in the 1960’s. They argued that deep squat is the most natural human posture and as such it cannot be harmful. The human fetus is in the deep squat position inside the mother’s womb. In most traditional societies people rather “sit” squatting down. You can still see this form of sitting in much of Africa and Asia.
Deep squat is also the posture of almost all small children when playing – a posture no one is teaching them.
Angle of knee flexion
Before we proceed to further explanation we must make clear how the knee flexion is measured. The angles we are referring to are actually not angles between the upper and lower leg as one might presume but rather between the flexed leg and straight leg.
So for instance 30 degree flexion is very shallow squat and over 90 degrees we are talking of deep squat.
Several studies followed in 1970’s and later (E. Meyers 1971, M. Steiner 1986, R. Panariello 1994) but none of them confirmed Klein’s findings (although some authors still speculated that squats below the 100 degree angle may pose danger to knee ligaments).
The studies found that the shear forces of PCL (Posterior Cruciate Ligament) peak at 90 degree flexion while the ACL (Anterior Cruciate Ligament) shear forces peak much sooner, at 15-30 degrees.
ACL and PCL are the two ligaments holding upper leg and lower leg together and typical knee injury involves one of these two ligaments (usually ACL).
It means that the knees are subject to greatest stress WITHIN THE RANGE OF SHALLOW SQUAT and the ligament forces are rapidly decreasing beyond the 90 degree angle (M. Sakane & colleagues, 1997; G. Li & colleagues 1999 and 2004; A. Kanamori & colleagues, 2000; K.L. Markolf & colleagues, 1996).
Also, no study found that people who are actually squatting deep do injure their ACL/PCL.
Therefore the only possible reason for injuries in deep squats is excessive stretching of ligaments. And this could be the case only if deep squat position was unnatural but as we explained above, this is one of the most natural postures of the human body. There are many unnatural movements and postures that athletes attempt in various exercises but deep squat is definitely not one of them.
It is most probably the strange western habit of sitting on elevated platforms (also known as chairs :)) which makes people scared of lowering their hips below the knee level…
But let’s return back to scientific studies. The 2001 study by R.F. Escamilla & colleagues found that weight lifters (regularly performing full squats with heavy weights) have stronger knee ligaments than the control group.
1991 Chandler & colleagues study came to the same conclusion as did Manariello and colleagues in 1994.
So here we come to the crucial question of knee mobility (and mobility of other joints, especially of hips). Knee mobility and flexibility is essential for prevention of injury and if your knee mobility doesn’t allow you to squat below certain level you are indeed in danger of getting hurt.
In such case it is necessary to start with exercises increasing the flexibility of the joints.
This is also the reason why most researchers recommend shallow squatting (up to 50 degree flexion) to patients recovering from knee injury.
Muscle fiber involvement
Most hamstring and quadriceps muscle fibers are recruited in the 80-90 degree flexion range. Therefore, lower squats do not directly increase benefit for hamstring and quadriceps development.
What does become significantly more involved are the muscle fibers of gluteus maximus (buttocks). This was clearly shown in a 2002 study by A. Caterisano & colleagues.
Gluteus maximus is a very large muscle and it’s often neglected, especially by male bodybuilders. Few people realize that this is also the single strongest muscle of the body core significantly influencing our performance in many exercises and activities.
Several studies confirmed the increased ligament strength in weight lifters. This is quite logical: if deep squats would lead to weak ligaments the weight lifters would ultimately failed in their sport (which is obviously not the case).
Also, deep squats have been shown to increase the ligament laxity (E. Meyers, 1971; R. Panariello, 1994; R.F. Escamilla, 2001; M. Steiner, 1986).
It should be noted that for every exercise involving the knee that is performed with weights equal or greater than the 1RM it is necessary to use some form of knee protection (wraps, sleeves or bends).
Medial and lateral meniscus is the part of the knee that is most susceptible to injury by deep squats.
The 1986 study by Nissel & colleagues showed that the maximum compressive forces affecting the menisci and articular cartilage peak at the 130 degree flexion angle.
There is, however, only dangerous to persons with injured knees as there is no evidence that meniscus problems can be actually caused by any form of squatting.
Would you ever consider flexing your arm only to 90 degree angle? Hardly so. Deep squats may or may not be suitable part of your training routine but if you are healthy and use proper technique you don’t need to worry about any risks associated with them.