physicians condemn squat,
citing how destructive they are to the tibiofemoral joints (knees),
despite scientific studies and millions of personal experiences
to contrary. One sports medicine doctor dared to explain to me
why squats were considered to be bad for the knees between his
sets of squats! Since sports medicine doctors only see people
with injuries, one can guess why they may have developed this
belief. The individuals they treat certainly do not constitute
a random sample, let alone a representative population, which,
as any scientist knows, is essential to even attempt to formulate
The NSCA position statement notes
"Some reports of high injury rate may be based on biased
samples. Others have attributed injuries to weight training,
including squat, which could have been caused by other factors.
Injuries attributed to squat may result not from the exercise
itself, but from improper technique, pre-existing structural
abnormalities, other physical activities, fatigue or excessive
An early study suggested, deep knee bends with weights (squats)
were hazardous to ligamentous structures of knee. Later studies
conclude squats improve knee stability if lifting technique does
not place rotary
stresses on the knee (Fleck and Falkel, 1986). The NSCA state:
"Squats, when performed correctly and with appropriate
supervision, are not only safe, but may be a significant deterrent
to knee injuries."
squat develops leg strength by imposing torques on the respective
joints. Joint torques are the product of the magnitude of the
force and the perpendicular distance from the line of force to
the center of the joints.
Torque force is necessary for muscles and joint structures
to adapt to respected overload. For example, if the knees do
not travel forward during the barbell squat, the quadriceps muscles
(ie: knee extensors) are not significantly loaded. On the other
hand, injury may result if knee (or low back) experience greater
torque forces than to what they are accustomed.
Contrary to propaganda, prominent weight training authorities
demonstrate squat with knees flexing forward at same distance
as hips flex backwards. Fredrick Hatfield, Ph.D., the first man
to squat over 1000 lbs, recommends knees to extend over feet
with back more upright for quadriceps development. Strength Training
for Young Athlete" by Steven
J. Fleck, PhD and William
J. Kraemer, PhD, illustrate parallel squats with knees extending
beyond feet (knees moving forward with similar magnitude as hips
Fry (2003) examined hip and knee torque forces of variations
of parallel barbels squats and concluded appropriate joint loading
during this exercise may require knees to move slightly past
Palmitier (1991) showed that knee shear forces are less in
the squat as compared to the seated knee extension. Closed chain
exercise like the squat can be more protective than open
chain exercise like the knee extension because it reduces shear
forces across the knee.
Typically the torque forces in the barbell squat are slightly
greater for the stronger hip joints as compared to the knee joint,
although both the knee and hips travel in opposite direction
away from the line of force. During execution of a barbell squat,
knees and hips travel in opposite directions away from the foot,
or away from center of gravity. Torque forces increase through
the knee, hip, spine and ankle as exerciser descends. The greatest
torque forces are experienced concomitantly through the hip,
spine, knee. and ankle when initiating the rise out of bottom
Torque on the Spine is greater when the torso is at a more
bent over angle and the bar is placed higher of the back of the
The practice of adopting foot rotation to selectively strengthen
individual muscles of quadriceps is not supported by literature
(Boyden 2000; Signorile 1995). Knee
rotation during squat can increase risk of injury (Fleck
& Falkel 1986). Signorile (1995) states:
"Extreme outward toe point greatly reduces stability,
it does not allow the proper drift of hips as lifter descends...
Extreme inward toe points are equally dangerous, coupling same
problems of stability, base size and lower body drift with added
danger of bringing knees together...this movement would place
high stress on all connective tissues."
Hips are extended by the Gluteus
Maximus and Adductor
The Quadriceps extend
the knee. Its involvement is increased when the knee travels
more forward relative to the ankle. Coactivation of the quadriceps
and hamstrings occurs to increase knee stability by functionally
reduce shear forces and strain across the knees. The three heads
(of 4 heads) of the Hamstrings
acting as Dynamic Stabilizers
by virtually shortens at the hip and simultaneously
'lengthen' at the knee (via quadriceps). When the knee is bent
>90, the tension of the hamstrings help stabilize the knee
by countering the anteriorly directed forces of the Quadriceps
(dislocating force) on the knee (see Components
of Force). The countering dislocating component with antagonist
stabilizing component is characteristics of closed chained exercises
(see Knee Stability).
Also see simplified diagram of countering forces next to Hamstring Weakness and
more detailed Quadriceps
and Hamstrings countering forces in somewhat an opposing
A wider stance increases Hip
Adductor involvement but does not appear to alter Quadriceps
or Biceps Femoris involvement
(McCaw and Melrose 1999). The Gluteus Maximus involvement increases
with a wider stance, but only at heavier load (eg: 75%).
The Spine is held ridged by the Erector
Spinae acting as a Stabilizer
with the Rectus Abdominis
and Obliques acting as
countering the pull of the Erector Spinae. Erector Spinaes involvement
is increased when spine is positioned at a greater forward angled.
Through the lower leg, Soleus
Planter Flexes the ankle allowing the shin to become upright
from the forward angled position at the bottom of the squat.
Like the Quadriceps, its involvement is increased when the knee
travels more forward relative to the ankle. The Gastrocnemius
acts as a Dynamic Stabilizer, virtually 'shortened' through the
ankle and 'lengthened' at the knee.
The mechanics of the squat change as the load increases. Hay
(1982) examining the effects of varying squat load observed changes
in the kinematics that effectively amounted to a technique change.
At lower loads a larger moment production was required by the
knee extensors (quadriceps). As the load increased (40, 60, and
80% of 1-RM) increase in forward inclination of the trunk was
noted, shifting the damand to the hip extensors.
Generally speaking, during a powerlift
type squat (bar lower behind the shoulders and a wider stance),
knee does not travel forward as far as bodybuilding
type squat. The hips typically travel back further with torso
bent forward on powerlift type squat unless the stance is substantially
wide, as in a sumo stance. However, a wide stance requires greater
hip torque (requiring greater strength through hip abduction)
while reducing both knee and spinal torque.
Although powerlifters have sizable trunk extension moments,
elite powerlifters have less forward trunk lean, less backward
displacement of the hips, yet less forward displacment of the
knees and bar compared to lower ranked powerlifters. Elite lifters
also have a slower descent into the lowest position (McLaughlin
Also see Qualitative Torque
Analysis (comparison image to above).
Full (Deep) Squat
(1996) illustrates safe position of a deep squat with the knees
extending beyond toes. Kreighbaum explains how deep
squat can be performed with little chance of injury to knee.
The variables of concern:
- speed of descent
- size of calves and thighs
- strength of controlling muscles
The primary danger to knee occurs when tissues of calf and
thigh press together, altering center of rotation back to contact
area creating a dislocation effect. The danger of knee injury
in this situation may be prevented if either of the following
factors are present:
- center of gravity of body system is kept forward of altered
center of rotation
- muscles of thigh are strong enough to prevent body from resting
or bouncing on calves.
Kreighbaum concludes deep squat is of little danger to knees
unless these variables and factors are disregarded. Certainly,
only limited type of athletes and performers may have the need
to perform a full squat. Olympic weightlifters commonly bounce
out of full front squat with near maximum resistances during
& Jerk and Snatch.
Incidentally, wide stance during Olympic-style
squat further reduces knee torque forces. Reportedly, those
proficient in Polzunec movement in style of Ukrainian national
folk dance appear to experience few orthopedic problems (up until
middle ages where their incident of orthopedic problems seems
to be no greater than general population) despite their ability
to perform a seemingly contraindicative movement for decades;
body upright, bounding from one leg to the other in deepest squat
position. Also see Over
During the lower portions of a deep squat or for some, even
a squat, lumber spine may flex if hip
flexibility is inadequate. The risk of low back injury is
increased during spinal flexion under a load if muscles of lower
back are not strong enough to support the flexed spine or if
joint structures have not progressively adapted to such movement.
Some believe that the depth of the squat should
stop just short of posterior pelvic rotation, also known as hip
wink. However, many individuals exhibit hip wink with no
lumbar pain or irritation, presumably adhering to Adaptation
Criteria. During a loaded squat, there appears to be a relatively
safe range of motion in which the lumbar spine can adapt (eg:
slight lumbar hyperextension to neutral or very slight lumbar
flexion). If hip mobility is insufficient to perform parallel
or full squats, particular hip flexibility exercises can be performed
in effort to eliminate or decrease spinal articulation throughout
the lower portion of the squat. See Full
Squat Flexibility and Deep
The squat can decrease knee injury (NSCA) and increase
leg power (Adams 1992) when implemented into a sound strength
and condition program. Early in off season, squat training will
develop foundation for more sports specific training, such as
plyometric work. See Conditioning
The strength and conditioning coaches may choose from a variety
of squat movements. The type(s) of squat(s) prescribed should
prepare athlete for specific biomechanical stresses demanded
by sport as well as other conditioning exercises. Coaches commonly
squat (wide stance, bar low on back, little knee torque)
at exclusion exercises with greater knee torque, namely Olympic
style front squat and bodybuilding
style squat. Coaches cite the importance of hip extension
strength and power. The Glutes are after all, the most powerful
muscles of the body.
Exercises that are most beneficial for sports performance
are generally those that are similar to the type of forces and
counter forces experienced on the playing field. See Training
Specificity and Resistance
Training for the Reduction of Sports Injury. The coach must
consider the unique biomechanic requirements of the sport, as
well as the requirements of each athlete's position. The hip/knee/ankle
torque ratio should be similar to actual biomechanics experienced
on playing field. Motor skills such as blocking, jumping,
leaping, etc. generally involve greater knee and ankle torque
than what is required of the traditional 'powerlifting' squat.
The 'bodybuilding' squat and power
training such as Olympic-style weightlifting and plyometrics,
require a higher ratio of knee/ankle versus hip torque than the
Conversely, some coaches cite knee injuries as a reason to
avoid any other squat than the 'powerlifting style' squat when
in fact the risk of knee injury may be attributed to other factors.
See squat safety above and Exercise
of Injury and Sports
If the body has not adapted to a greater
torque force, injury can result. It is not necessary to avoid
torque force if muscles and joint structures can adapt. See adaptation criteria.
Of hip and knee joint, knee is more vulnerable to injury than
hip due to structural and functional differences. Certainly,
if an individual has had a history of knee pain associated with
these types of movements, squat can be modified to to place more
torque on hip and consequently less on the knee joint. Based
on the above analysis, this can be accomplished two ways. Simply,
by not squatting down all the way (e.g. 90°) both knees and
hip do not experience as great of torque forces. Although, this
decrease may be offset by tendency to add more weight to exercise.
Alternatively, by bending at hip more than the knee, the knee
will travel forward less, as in powerlifting type squat. Recall,
quadriceps will not be exercised as intensely since there is
less torque on knee joint. In addition, since balance must be
maintained over the feet, bending over not only transfers more
torque to hips, the torque forces through spine (lower back)
increase, another vulnerable joint for some. Certainly a compromise
must be made to evenly distribute torque force between knee and
hip/lower back, particularly when both knees and lower back are
If the ankle is not flexible enough
to allow knee to travel forward sufficiently, the back will need
to be bent forward more to maintain center of gravity within
foot base. Consequently, lower back will be subjected to greater
torque forces. Squatting with feet wide apart can alleviate part
of the problem, allowing back to be positioned more upright.
This solution does not, however, distribute equal stresses on
quadriceps and glutes as would be possible with adequate ankle flexibility.
Until flexibility can be restored, a temporary solution is
to elevate the ankles on board or platform. This will allow knees
to travel forward same distance as hip travels backwards. Elevating
heels may present a risk to individuals with adequate ankle flexibility
who have not adapted to greater torque forces through knee. In
which case, knees can potentially travel forward more than what
they are accustomed to. Even when elevating heels with insufficient
ankle flexibility, resistance should begin light and progress
incrementally every workout until a true workout weight is achieved,
so joint adaption can occur.
Obviously, individuals who are at higher risk for specific
types of knee pain may choose to perform powerlifting
squat or box
squats while avoiding certain exercises specifically designed
to emphasize quadriceps' involvement by increased knee torque
hack squat, leg
extension). Likewise, individuals who are prone to particular
types of lower back problems may favor the weighted
squat or leg
press while avoiding certain exercises specifically designed
to emphaisis torque on spine increasing lower back torque (e.g.
- Boyden G, Kingman J, Dyson R, (2000). A comparison of quadriceps
electromyographic activity with the position of the foot during
the parallel squat. J Strength Cond Res. 14(4): 379-382.
- Fleck SJ. and Falkel JE (1986). Value of Resistance Training
for the Reduction of Sports Injuries. Sports Medicine,
- Fry AC, Smith JC, Schilling BK (2003). Effect of knee position
on hip and knee torques during the barbell squat. J Strength
Cond Res. (4):629-33.
- Hatfield, F.C. (1989). Power: A Scientific Approach, Contemporary
- Hay JG, Andrews JG, Vaughan CL (1982). The biomechanics of
strength-training exercises. Proceedings of the 10th International
Conference of Sport, Physical Education, Recreation and Dance;
- Kraemer, W.J., Fleck, S.J. (1993). Strength Training for
Young Athletes, Human Kinetics.
- Kreighbaum, E., Katharine, B.M. (1996). Biomechanics; A Qualitative
Approach for Studying Human Movement, Allyn & Bacon, 4, 203-204.
- McCaw ST, Melrose DR (1999). Stance width and bar load effects
on leg muscle activity during the parallel squat. Medicine and
Science in Sports and Exercise; 31(3): 428-436.
- McLaughlin TM, Dillman CJ, aand Lardner TJ (1977). A Kinematic
model of performance of the parellel squat. Medicine and Science
in Sports. 9:128-133.
- National Strength and Conditioning Association. The Squat
Exercise in Athletic Conditioning, NSCA Position Statements.
- Palmitier RA, An KN, Scott SG, Chao EY (1991). Kinetic chain
exercise in knee rehabilitation. Sports Medicine; 11: 402-413.
- Signorile JF, Kwiatkowksi K, Caruso JF, Robertson B, (1995).
Effect of foot position on the electromyographical activity of
the superficial quadriceps muscles during the parallel squat
and knee extension. J Strength Cond Res. 9:182-187.
Most line drawings from Trainer