Squats are arguably the most popular exercise performed. Ball, wall, deep, mini, single leg, bosu…there are so many forms that can be applied to many circumstances. For athletics the squat primarily strengthens the hips, thighs, and back, but because it is a closed chain exercise, it is also used in rehabilitation settings (Escamilla 2000). However, there should be some care used when completing a squat.
Shear and compressive forces do act on the knee during a squat. Shear is a force directed parallel to a surface and compression is a pressing or squeezing force directed axially through a body (Hall 2007). Shear forces against the tibiofemoral joint (the knee) can injure the ACL and PCL, and compression forces can damage the menisci and the articular cartilage (Escamilla 2000). In the case of a squat, the shear force is acting parallel to the tibia plateau (top of the larger shin bone) (Hall 2007). In addition, forces acting on the patellofemoral joint (where kneecap meets thigh bone) create stress (distribution of force with in a body – quantified as forces divided by the area over which the force acts, Hall 2000) on the articular cartilage of the patella and the femur (Escamilla 2000).
Low shear forces are generated between 0 and 60 degrees of knee flexion and Patellofemoral and tibiofemoral compressive and shear forces increase as the knees flex and decreas as the knees extend. For rehabilitation purposes it is recommended that squats be performed to no deeper than 50 degrees (Esamilla 2000).
Activity of the quadriceps is greatest between 80-90 degrees, peak hamstring activity is between 50 and 70 degrees, and gastrocnemius (calf) activity was greatest between 60-90 degrees of knee flexion. These findings indicate that a deeper squat, past 90-100 degrees, does not increase the benefit (Escamilla 2000).
Keep in mind that some activities do require a deep squat, but for most of us mere mortals, parallel should suffice.
Escamilla, R. (2000) Knee biomechanics of the dynamic squat exercise. Medicine and Science in Sport and Exercise, American College of Sports Medicine 0195-9131/01/3301-0127
Hall, S. (2007) Basic biomechanics. McGraw Hill, NY, NY.
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