Squat Analysis

Torque Force | Rotary Force | Full Squat | Sports Performance | Customization

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Safety

Barbell SquatSome physicians condemn squat, citing how destructive they are to knees, despite scientific studies and millions of personal experiences to contrary. One sports medicine doctor explained to me why squats were considered to be bad for knees. He was actually telling me this 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 inferences.

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 training."

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."

Torque Force

Bodybuilding-style Squat Qualitative Torque AnalysisContrary 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 800 lbs, recommends knees to extend over feet with back more upright for quadriceps development. "Strength Training for Young Athletes" by Steven J. Fleck, PhD and William J. Kraemer, PhD, illustrate parallel squats with knees extending beyond feet (knees moving forward with same magnitude as hips moving backwards).

Torque force is necessary for muscles and joint structures to adapt to respected overload. If knee does not travel forward during the barbell squat, quadriceps muscles (ie: knee extensors) are not significantly exercised. On the other hand, injury may result if knee or lower back experience greater torque forces than to what they are accustomed.

Fry et. al. (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 the toes.

Torque through hip active not only activate the Gluteus Maximus and Adductor Magnus, but also three heads of the Hamstrings which cross both the hip and knee. Torque through knee activate Quadriceps. Through knee, the dislocating forces of the quadriceps are countered by stabilizing forces of hamstrings. See diagram of countering forces next to Hamstring Weakness. Also see Knee Stability.

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 both through knee and hip joints as exerciser desends. The greatest torque forces are experienced when initiating the rise out of bottom position.

Try this simplified qualitative method in determining relative torque forces in the knee and hip joints. First, take a photograph of barbell squat in a full descent with a perspective perpendicular to joints plane. Draw a line of force through resistance on its center of gravity, straight up and down, parallel to force of gravity. Gravity acting on both body mass and added mass (barbell) contribute to resistance. Incidentally, compression forces act upon joints during squat stance. On barbell squat, center of gravity is over instep (between forefoot and heel). If it is not, individual will fall over, toward center of gravity.

Now, draw three separate horizontal lines, perpendicular to line of force from each joint articulation (ankle, knee, and hip) to line force. If image is not exactly viewed from the side, "horizontal" lines can be drawn in perspective to picture as shown. Once diagram is complete, a relative comparison can be made on the torque forces of the hip, knee, and ankle.

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. 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. This emphasizes stronger hip extensors and adductors and consequently reduces knee extensor involvement. Knee torque is further reduced by a wide stance.

Powerlifitng-style SquatBarbell SquatAlso see Qualitative Torque Analysis (comparison image to above)

Rotary Force

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 and Falkel, 1986). Signorile, et. al. 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."

Full (Deep) Squat

Barbell Full SquatKreighbaum (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 both Clean & 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 Generalizations.

During lower portions of deep squat, lower back may flex if hip flexibility is inadequate. The risk of low back injury is increased if muscles of lower back are not strong enough to support the flexed spine or joint structures have not progressively adapted to such stress. Flexibility exercises can be performed if hip flexibility is insufficient for deep, or full, squats. See Full Squat Flexibility and Deep Squat Test.

Sports Performance

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 Work recommendations.

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 prescribe powerlifting 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 'powerlifting' squat.

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 Safety: Causes of Injury and Sports Conditioning.

Customization

Box SquatIf 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 healthy.

Box Zercher SquatIf 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 only 5-10% 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 while avoiding certain exercises specifically designed to emphasize quadriceps' involvement by increased knee torque (e.g. front squat, sissy squat, safety squat, barbell 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 lower back involvement by increased lower back torque (e.g. powerlifting squat, deadlift).


    1. 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.
    2. Fleck, S.J. and Falkel, J.E. Value of Resistance Training for the Reduction of Sports Injuries. Sports Medicine, 3, 61-68, 1986.
    3. Fry AC, Smith JC, Schilling BK. Effect of knee position on hip and knee torques during the barbell squat. J Strength Cond Res. 2003 Nov;17(4):629-33.
    4. Hatfield, F.C. (1989). Power: A Scientific Approach, Contemporary Books, pg. 158.
    5. Kraemer, W.J., Fleck, S.J. (1993). Strength Training for Young Athletes, Human Kinetics.
    6. Kreighbaum, E., Katharine, B.M. (1996). Biomechanics; A Qualitative Approach for Studying Human Movement, Allyn & Bacon, 4, Pgs 203-204.
    7. National Strength and Conditioning Association. The Squat Exercise in Athletic Conditioning, NSCA Position Statements.
    8. 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 ClipArt.


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