By Jordan Feigenbaum MS, CSCS, HFS, USAW Club Coach
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One frequent comment I hear when discussing squats is that they’re “bad for the knees”. This is especially true when conversing with various health professionals like doctors, chiropractors, physical therapists, etc. even though they haven’t really analyzed the movement to a great enough degree to validate this opinion.
The more likely reasoning behind this repetitive bashing of squats is that many of the patients they see present with certain knee issues that likely result from overuse and repeated impacting of the joint, i.e. frequent running, jumping, and agility dependent recreational sports like tennis, soccer, pick-up basketball and the like. Perhaps the most interesting thing about squats and injuries to the knee joint is that they do not occur very frequently during training. I have personally witnessed atrocious squats day-in and day-out over the better part of a decade, whilst never witnessing someone collapsing from an acute knee injury. Sure, it’s feasible that someone could injure a ligament, meniscus, tendon, or other vulnerable structure during this (or any) movement, but this is not frequent enough to even discuss further. Anybody involved in the training world must recognize that resistance training and competitive weightlifting has the lowest rate of injury per participation hour of almost any other activity. Check out this table:
Another source of commentary on this Karl K. Klein and Fred L. Allman, Jr.’s book The Knee in Sports that was published in the 1961. Klein and Allman did research on athletes and Olympic weightlifters who squatted and concluded that certain squatting styles led to “loose knee ligaments”. He goes on to recommend squatting to just below parallel (not A** to grass) and performing front squats in addition to maintaining the proper alignment between the knees and the toes. In his opinion, allowing the knees to come in (as compared to the foot position-i.e. valgus knee) was a form error and could lead to injury. He therefore recommended that a trainee should keep their knees in-line with the toes during the entirety of the movement and should only squat to just below parallel. Someone from these it was determined that squats are “bad for the knees” and should be avoided, even though this was never even implied in this text. Tommy Suggs, a former world-class lifter, shares his commentary here.
Numerous texts have been published since this 1961 book to dispel this and other myths. A study showed that powerlifters and weightlifters both had tighter knees (more developed soft tissue) than non-trained controls (Chandler and Stone 1991). Manariello, Backus, and Parker published a paper in a 1994 issue of the American Journal of Sports Medicine that showed that the hamstring’s involvement in the squat plays a role in protecting the anterior cruciate ligament. According to a study done by McLaughlin, Lardner, and Dillman in a 1978 issue of Research Quarterly, the low back muscles are used primarily in an isometric function, that is they simply stabilize the spine and trunk, and not shorter or lengthen under load. This effectively trains these muscles in their proper function, thereby making the squat a functional exercise for the back as well as the legs. More information can be found here with various squatting myths and their scientific rebuttals.
The main purpose of this article is to show why squatting is not bad for the knees, with a secondary aim to prove that squats are actually beneficial for this joint. With this in mind, it’s probably important to qualify what I mean when I say squat. When I refer to the squat from this point on, I am referring to the low-bar back squat and not the high-bar back squat, front squat, or overhead squat. While all of these variations have certain appropriate applications, the low-bar back squat fits the criteria for exercise that satisfies the basic tenets of training that are as follows:
AN APPROPRIATE EXERCISE SHALL MEET ALL THE FOLLOWING:
1) Uses the most muscle mass possible
2) Longest possible range of motion that is effective*
3) Generates most force production possible
*this denotes that a longer range of motion is not always advantageous. For instance, in the squat it is possible for a lifter to increase the range of motion by squatting well below parallel. This however, violates the other tenets of our training model, as performing a squat this way decreases the musculature utilized and decreases force production as certain muscle must relax to achieve this depth and less weight can be effectively moved if this type of squat is utilized.
Thus, any exercise that fits these threerules has a standardized model that all repetitions must be compared to in order to ensure the lifter is using the correct form. Any rep that deviates significantly from this standardized model represents a decreased efficiency on some level and must be corrected by their coach. If you don’t believe that an ATG squat requires both relaxation and decreased weight than a standard low-bar back squat then let’s look at the following picture:The high-bar squat on the left shows a lifter whose knees are further forward OVER the toes, a more upright torso, and shortened hamstrings. The lifter on the right shows the low-bar back squat with the lifter’s back being more horizontal, his knees somewhere over the middle of the foot, and lengthened hamstrings. The high bar squat has a longer rang of motion, as the depth is well below parallel, however the lifter’s hamstrings are not recruited heavily in this type of squat. This makes this type of squat more anterior dominant, as the quadriceps must move the weight without significant contribution from the hamstrings (the muscles posterior to the knee) to stand back up. So although the range of motion is increased (Rule number 2), the hamstrings have relaxed and subsequently less weight can be moved (Rules 1 and 3). The low-bar back squat effectively uses the back as a lever as it’s locked into its natural anatomical position, lordosis, and keeps the forces on the knee joint balanced front to back and side to side. The high-bar back squat requires that the force be shifted more anteriorly, as the quadriceps are the primary mover, and also does not train the back as functionally as the low-bar back squat since the back is not as horizontal. In a properly performed low-bar back squat the knees are not subject to extreme forces that could be considered overtly injurious to either the soft tissue structures or bony constituents of the joint. While the knee is technically a pivotal hinge joint, allowing for flexion and extension as well as slight medial and lateral rotation, in a correctly performed back squat the knee functions as a hinge joint only, undergoing flexion and extension. In this correct version of the squat there is no rotation of the femur about the tibia and the patella tracks correctly during both the eccentric and concentric portions of the movement. Moreover, with correct execution of the squat the knee joint will only be exposed to uniform forces, both anteriorly and posteriorly as well as medially and laterally. Finally, it can logically be concluded that correctly training the squat and the subsequent adaptations both morphologically and functionally will be to the benefit of the lifter in activities of daily life and sport.
The stresses on the knee joint can be sub-divided into mechanical stresses and muscular stresses. For this discussion mechanical stresses will be considered those to be caused by the barbell and its load, whereas muscular stresses will be limited to the forces caused by muscular activity of the skeletal muscle acting on the knee joint. Let’s first address the mechanical stresses on the knee joint exhibited by the barbell.
In every barbell exercise the bar and its load must remain in balance over the mid-foot for correct execution of the lift and the squat adheres to this rule. In the low-bar back squat the barbell is carried on the shoulders in a position just inferior to the spine of the scapula. The barbell, loaded or not, has a vector force created by gravity that’s direction is vertically downward to the ground. Again, this is balanced over the mid-foot of the lifter. When the lifter has walked the barbell out of the rack and is standing completely upright the lumbar spine, hips, and knees are all in normal anatomical extension. Additionally, at this point there exists no moment arm and subsequently, no torque about any of these joints as the skeletal components are all aligned. The only forces on the lifter at this point are compressive forces, from the barbell on the skeletal components of the lifter, and tension of the lifter’s muscles supporting the skeleton against the load. This compressive force is uniform across the knee joint and should not be considered injurious to it. Bearing weight in the confines of normal anatomical position is generally not contraindicated in a healthy specimen.
During the correct performance of the low-bar back squat the only additional mechanical force on the knee joint occurs during the descent and ascent of the movement. At the initiation of the descent of the squat the hips and knees enter into flexion and the barbell remains in balance over the mid-foot. The barbell’s vertical vector force created by gravity crosses the diaphysis of the femur to create proximal and distal levers, with the distal lever acting on the knee joint. The moment arm is the distance from where the barbell’s vertical vector crosses the femoral shaft to the center of the knee joint and the torque on the knee joint is thus the product of the barbell’s weight and this distance. Of special importance here is the fact that this lever is relatively short compared to the proximal femoral lever. This effectively places more of the weight on the hip and its relevant structures while the knee joint is only exposed to a small amount of torque comparatively. While this is indeed a mechanical force (torque) that the knee is exposed to, it is also a uniform force that evenly loads the menisci and other relevant soft tissue structures. This force does not cause the knee to rotate twist about its axis either, which lets the knee joint function as a pure hinge joint. In short, the knee does not deal with a large percentage of the load and the weight it does see it distributed evenly across the entire joint. Now let’s discuss the muscular forces acting upon the knee.
The two muscle groups that cross the knee joint and act upon it, the hamstrings posteriorly and quadriceps anteriorly. The hamstrings muscles are comprised of four muscles, the semimembranosus, semitendinosus, long head of biceps femoris, and short head of biceps femoris. All of these muscles flex the knee and with the exception of the short head of biceps femoris, the also extend the hip. The quadriceps are comprised of the rectus femorus, and the vasti muscles (medial, intermedius, and lateralis). All of these muscles act to extend the knee by inserting into the patella via the quadriceps’ tendon that is connected to the patella. The patella is subsequently attached to the tibial tuberosity via the patellar ligament, which is how the action of knee extension is exerted. The rectus femoris muscle also crosses the hip joint to act as a hip flexor.
Before the descent of the squat the lumbar and thoracic spinal segments are locked together with the pelvis with isometric contraction of the erector spinae muscle group. The ischial tuberosity of the pelvis is the origin of three of the hamstrings muscles (not the short head of the biceps femoris) and with the pelvis locked into position proximally, this allows for maximal hamstring activity in the low-bar back squat as the pelvis is not allowed to move and thus put slack into the hamstrings. Once the squat is initiated the back angle starts to become more horizontal as the hips and knees enter flexion. Because the hamstrings muscle group both extends the hip and flexes the knees, the hamstring is stretched proximally and shortened distally. This means that the hamstring acts isometrically once it is stretched to anchor both the hip joint and knee joint. As for the quadriceps, they lengthen as the knees flex, with the possible exception of the rectus femoris, as it is a hip flexor and the hips are also flexing. At any rate, as the descent of the squat increases we can consider the hamstrings to be maximally stretched and acting posteriorly to the knee, whereas the quadriceps are also maximally stretched and acting anteriorly to the knee. It should be fairly obvious that at the bottom of the squat, which is when the crease of the hips is 1” below parallel, that the net force on the knee anterior to posterior is zero. This is due to the synergistic activity of both the hamstrings and quadriceps muscles in the correct performance of the low bar back squat. Because the net force on the knee approximates zero from anterior to posterior, the anterior and posterior cruciate ligaments are not called upon to prevent anterior or posterior translation of the tibia relative to the femur, thus these important ligaments are not affected detrimentally during a squat.
You see, the low bar back squat demands a more horizontal back angle than other squats. Furthermore, this requires the hamstrings to be maximally engaged to anchor the back angle while the knees flex but do not move forward at the bottom of the squat. If the knees move forward at the bottom of the squat the lifter has failed to maintain the appropriate back angle, i.e. he or she has assumed a more vertical back angle, and thus has introduced slack into the hamstrings. Additionally, the now vertical back angle increases the length of the moment arm of the distal femoral lever, thereby increasing the torque on the knee joint. So now you can see that by performing a correctly executed low-bar back squat we are in no danger of hurting the knees.
(continued at http://www.dynamicfitnesscoach.com).