I don't know how it started, but I am assuming that it probably started
with physical therapists and rehab professionals who learned in school
that when the knees pass the toes in a squat this places a lot of stress
on the knee and can damage the structure and integrity of the joint.
While
I will agree that improper squatting patterns can get you injured and
that an overly knee-dominant squat (not properly engaging the hips) is
probably not the best thing for you, especially under load, I can't see
how you can squat down to an appropriate depth (femur parallel to the
floor) without the knees slightly breaking the plane of the toes. I
think the biggest problem with this myth stems from the sad fact that
most rehab professionals have eliminated the squat from their exercise
protocol, deeming it "to dangerous." Because of this, most rehab
professionals are clueless with regard to how to properly and safely
coach a squat, which is silly because the squat is a fundamental
movement of life. Telling someone not squat is like telling them "don't
sit on the toilet ever again" or "never pick anything up off the bottom
shelf at the supermarket." The problem isn't the movement itself, it is
that people don't understand the movement (since it isn't taught to them
properly) so they end up getting hurt when they need to perform it in
their daily routine.
While there may be certain instances that teaching a full squat would be
unsafe, it is not appropriate to take information on people with
specific injuries and pathologies and apply it to all clients/patients.
Everything from research to exercise prescription is highly population
specific and you need to understand just whom you are working with and
what rules apply. For the majority of people, the squat should be a
fundamental movement taught in both rehab and gym settings.
Don't Let The Knees Pass The Toes!
The statement, "don't let the knees pass the toes", has been uttered by
many doctors, coaches, trainers, and physical therapists. While a lot of
strength coaches and personal trainers now seem to "get it" with regard
to the knees passing the toes not being such a bad thing, this myth
just wont seem to die.
The squat is a coordinated lift, which requires both mobility and
stability at a variety of joints up the chain. The ankles, knees and
hips go through active movements of flexion and extension (dorsiflexion
and plantar flexion at the ankle) to perform the squat lift. However,
the torso should remain stable during the squat, especially under load,
and maintain an angle that is approximately parallel to the shin
(relatively speaking since people will have variations in limb length
and torso length).
In order to keep the knees from passing the toes, some practitioners
advocate the shin remaining more vertical, which changes the mechanics
of the squat, as knee flexion will be limited during the eccentric
portion of the lift. In order to reach an appropriate depth, the client
would then have to push their hips back even further than normal,
forcing the trunk to bend over further. While this technique may seem to
be more "knee sparing", it tends to place greater load on the lumbar
spine.
A 2003 study by Fry et al. evaluated the joint kinetics during a squat
when forward displacement of the knee was restricted (IE, the squat I
just described) vs. when forward displacement of the knee was allowed
(IE, a normal squat where the knees can pass slight forward of the
toes). While knee torque was slightly less during the squat where
forward displacement of the knees was restricted, hip torque was
increased almost 11 times greater than when forward displacement of the
knees was allowed. The researchers concluded that, "Although restricting
forward movement of the knees may minimize stress, it is likely that
forces are inappropriately transferred to the hips and lower-back
region. Thus, appropriate joint loading during this exercise may require
the knees to move slightly passed the toes."
Squatting Deep Is Bad For Your Knees!
The squat is used in weight rooms all over the world to prepare athletes
for competition; however, safe depth is often argued between strength
coaches and athletic trainers. It is typically understood that
patellofemoral joint forces are increased during the eccentric portion
of the squat at greater angles of knee flexion. A 2001 study published
in Clinical Biomechanics looked at patellofemoral joint kinetics during
three different squat depths (70 degrees, 90 degrees and 110 degrees of
knee flexion). Researchers Salem and Powers hypothesized that
patellofemoral joint reaction force would increase with increased knee
flexion; however, patellofemoral joint stress would remain constant
through the greater squat depths. They based this hypothesis on the idea
that with increased flexion, patellofemoral joint contact area has also
been shown to increase in previous cadaveric studies, leading them to
believe that increased joint contact area would better distribute joint
force over a larger area and maintain or potentially decrease
patellofemoral joint stress.
Before continuing, I should note that a squat to 70 degrees of knee
flexion is about a quarter squat, a squat to 90 degrees of knee flexion
is a half squat and a squat to 110 degrees of knee flexion would be
closer to a full squat (IE, femur parallel to the floor).
Out of the three depths, 70, 90 and 110 degrees, the full squat (110
degrees) produced the highest amount of patellofemoral joint reaction
force (5097.1 N). However, this was not found to be statistically
different than the joint reaction force of the 70-degree shallow squat
(4319.2 N) or the 90-degree half squat (5065.7 N). Similarly,
patellofemoral joint stress was greater in the 110-degree squat (12.3
MPa), however, this again was not statistically different than the
70-degee (10.8 MPa) or 90-degree (11.7 MPa) squat.
From this study, it appears that the consistent knee extensor moment
created little variation in patellofemoral joint force or stress when
squatting from 70 to 110 degrees of knee flexion. This led Salem and
Powers to conclude, "The results of this study do not support the
premise that squatting to 110 degrees places greater stress on the
patellofemoral joint than squatting to 70 degrees. These findings may
have implications with respect to safe design of athletic training
regimens and rehabilitation programs."
Leg Press And Hack Squat Are Safer Than Barbell Squats!
Gym goers and personal trainers tend to favor things like the leg press,
hack squat machine, and smith machine over the regular barbell squat
stating that, "they're safer than regular squats". In addition, many
rehab clinics have a leg press machine or some sort of total gym machine
(which behaves similar to a hack squat), or they teach their patients
to squat with their back against a stability ball placed against the
wall (wall/ball squat). While I don't deny that in a rehab setting these
options may be necessary for some, it should be the goal to eventually
progress the patient from the controlled environment of the leg press or
wall/ball squat to a free standing squat (even if it is just body
weight). The goal of rehab should be to rehabilitate the patient back
into normal life. By having them only leg press or wall/ball squat and
telling them to not perform regular squats ever again because they are
"unsafe", is doing the patient a total disservice since they will need
to call on this pattern at some point in their daily activities.
Escamilla et al., looked at knee forces and muscle activity during a
squat and leg press under a variety of technical variations using a load
equal to the subjects 12RM. The squat variations included a squat with a
narrow stance or a wide stance and with feet pointed either straight
ahead or externally rotated to 30 degrees. The leg press variations
included a leg press performed with the feet high on the footplate or
the feet low on the footplate. In addition, the subjects were asked to
use both a wide stance or a narrow stance in both the high and low foot
placement.
Co-contraction of the quadriceps, hamstrings and gastrocnemius is
extremely important for stability of the knee and has been shown to help
decrease stress on the anterior cruciate ligament (ACL). During the
knee extension phase of this study, the squat displayed a greater
co-contraction of these muscles than leg press at either the high or low
foot placement, implying that "the squat may be a more effective
exercise for quadriceps and hamstring development compared with the leg
press."
However, while ACL forces were not produced in either the squat or leg
press variations (which may be due to hamstring activity), posterior
cruciate ligament (PCL) forces were greater in the squat compared to
either leg press variation. This could have specific implications for
individuals who are rehabilitating a PCL strain.
Patellofemoral compressive forces were increased at great angles of knee
flexion for both the squat and the leg press. This was shown in the
study discussed in the previous section by Salem and Powers. Escamilla
et al. state, "Performing the squat, leg press high and leg press low
within the functional range of 0-50 degrees may be most active for
athletes or patients with patellofemoral pathologies. However,
performing the squat, leg press high and leg press low at greater knee
flexion angles may not be problematic for athletes with healthy knees as
long as healthy loads are not used exclusively."
I wonder about their 0-50 degrees of squatting recommendation, as that
is an extremely short range of motion to go through. That is even less
than the 70-degree squat used by Salem and Powers. In addition, if the
athlete or patient is rehabilitated properly, should they not be able to
squat to appropriate depths, given the fact that at the greater knee
angles more muscle activation should occur. This would probably be up to
the rehab professional or maybe even the trainer working with the
client as to understanding progression and knowing when the individual
is ready to move forward with their training program, rather than just
doing the same thing over and over and becoming stagnant. Anecdotally, I
have improved squat range of motion in clients I have worked with and
myself, after suffering from some knee issues in the past. The quote
above does imply that knee ranges of motion during the squat or leg
press will vary given the individuals specific condition (IE,
limitations for those with pathologies and normal ranges of motion with
those who are healthy), however, would proper squat depth right off the
bat, when the individual is not pathological, help to prevent these
pathologies from occurring? I would think so!
The researchers go on to conclude that, "The greater muscle activity and
knee forces in the squat compared with the leg press low and leg press
high implies that the squat may be more effective in muscle development
but should be used cautiously in those with PCL and patellofemoral
disorders, especially at greater knee flexion angles. Because all forces
increased with knee flexion, training within the functional 0-50 degree
range may be efficacious for those whose goal is to minimize knee
forces. The lack of ACL force implies that all exercises may be
effective during ACL rehabilitation."
A more recent study (2009) by Escamilla et al. compared patellofemoral
joint force and stress between a one-leg squat, a wall squat with the
feet close to the wall, and a wall squat with the feet further from the
wall.
For those that are unfamiliar, the wall squat is a squat performed with
the back against a wall. This is similar to the wall/ball squat and the
position is also similar to a hack squat or total gym squat in that the
feet are typically out in front of the torso rather than centered
underneath it, which changes the mechanics of the squat greatly. This is
also the way that some choose to perform their smith machine squats,
which is nothing more than an accident waiting to happen in my opinion.
In this study, the wall squat was performed while holding dumbbells down
at the side. A towel was also placed between the lifter and the wall in
order to prevent friction and allow for a smooth squat movement.
While discussing the one-leg squat in the introduction of this paper,
the researchers note, "Performing a one-leg squat also causes the stance
knee to translate forward beyond the toes at the lowest position of the
squat. Clinicians and trainers often believe that anterior translation
of the lead knee beyond the toes during squatting type exercises
increases patellofemoral joint force and stress, but there is currently
no evidence to support this belief."
The wall squat long and short exercises both produced higher
patellofemoral joint forces and stress when compared to the one leg
squat. The wall squat short also produced a higher amount of force and
stress at a 90-degree knee angle when compared to the wall squat long.
This was thought to occur because the knees in the wall squat short went
further passed the toe, changing the direction of patellar tendon force
and potentially increasing patellofemoral force, than in the wall squat
long, where the shins remained fairly vertical.
However, the knees also migrated passed the toe a similar amount in the
one-legged squat, but this exercise produced less joint force and stress
than the wall squat short. The cause of this was the greater amount of
quadriceps force during the wall squat short. The quadriceps force was
approximately 30-40% greater at 70-90 degrees of knee flexion in the
wall squat short compared to the one-legged squat. In addition, at those
same knee angles (70-90 degrees) hamstring force in the one-leg squat
was 60-70% greater in the one-leg squat! The researchers made some
extremely important observations:
1.) The increased quadriceps force and decreased hamstring force it the
wall squat short is due to the fact that the trunk is erect in the wall
squat and is tilted approximately 30-40 degrees in the one leg squat.
2.) The wall squat required a greater amount of knee extension because
the erect trunk produced a line of force from the center of mass (the
lifters mass plus the dumbbells held at the side) decreasing the ability
of the hip extensors to contribute.
3.) The forward trunk tilt in the one-leg squat produced a line of force
from the center of mass which allowed for a larger hip extension
contribution
These three points are critical because they highlight the importance of
maintaining the center of mass over the base of support (which takes
place in a normal squat). In a hack squat, wall squat, wall/ball squat,
total gym machine squat, or the way some perform a smith machine squat,
the center of mass is displaced behind the base of support (the feet are
out in front) which does not adequately allow the hip extensor
mechanism to contribute to the movement.
The researchers went on to conclude that, "Except at 60 and 90 degree
knee angles, patellofemoral joint forces were similar between the wall
squat short and the wall squat long. Between 60 and 90-degree knee
angles, wall squat exercises generally produced greater patellofemoral
compressive force and stress compared with the one-leg squat."
In the video below Patrick demonstrates proper squat technique:
Conclusions
Clearly it appears the myths surrounding squats are not founded on
scientific information, but rather anecdotal evidence passed down from
teacher to student in classrooms all over the world.
Squatting is safe and is an extremely important movement for everyone to
learn as it is performed frequently in our daily lives (just think
about how many times a day you sit down to your computer desk and then
get back up).
Obviously there are specific instances where squatting may be
contraindicated for certain individuals and it is up to the clinician or
trainer to understand their client and screen out any potential factors
that may prevent the client from safely performing a squat.
As the research suggests, those with specific knee pathologies may
benefit from a reduced range of motion. However, I would argue that the
rehabilitation program should focus to rehabilitate the patient to
safely performing a squat down to a depth that would be needed in daily
life, for example, sitting down to a chair, which is probably right
around 90 degrees of knee flexion if not a little more.
I should also note that back squatting might not be appropriate for
every client. Often times, physical therapists and rehab professionals
here the word "squat" and immediately think of someone with a load of
weight on their upper back, which is why they may shy away from this
exercise for their patients. Squats can be performed a variety of ways -
front squat, back squat, trap bar, DB squat, kettlebell squat, as well
as any of the several single leg variations, such as split squats,
lunges, Bulgarian squats, or 1-leg squats. It is important to emphasize
that people should first be taught how to squat with just their body
weight, as this is an important pre-requisite to loading the client.
If you are still doing curls in the power rack, chances are this paper just went way over your head.
References
1. Fry AC, Smith JC, Shilling BK. Effect of knee position on hip and
knee torques the barbell squat. J Strength Cond Res. 2003;17(4):
629-633.
2. Salem GL, Powers CM. Patellofemoral Joint Kinetics During Squatting
in Collegiate Women Athletes. Clinical Biomech. 2001;16:424-430.
3. Escamilla RF, Fleisig GS, Zheng N, Lander JE, Barrentine SW, Andrews
JR, Bergemann BW, Moorman CT. Effects of technique variations on knee
biomechanics during the squat and leg press. Med Sci Sports Exerc.
2001;33(9):1552-1556.
4. Escamila RF, Zheng N, Macleod TD, Edwards WB, Imamura R, Hreljac A,
Fleisig GS, Wilk KE, Moorman CT, Andrews JR. Patellofemoral joint force
and stress during the wall squat and one-leg squat. Med Sci Sports
Exerc. 2009;41(4):879-888.