Info on Squats:
There are several schools of thought on squat depth. Many misinformed individuals caution against squatting below parallel, stating that this is hazardous to the knees. Nothing could be further from the truth. (2) Stopping at or above parallel places direct stress on the knees, whereas a deep squat will transfer the load to the hips,(3) which are capable of handling a greater amount of force than the knees should ever be exposed to. Studies have shown that the squat produces lower peak tibeo-femoral(stress at the knee joint) compressive force than both the leg press and the leg extension.(4) For functional strength, one should descend as deeply as possible, and under control. (yes, certain individuals can squat in a ballistic manner, but they are the exception rather than the rule). The further a lifter descends, the more the hamstrings are recruited, and proper squatting displays nearly twice the hamstring involvement of the leg press or leg extension. (5,6) and as one of the functions of the hamstring is to protect the patella tendon (the primary tendon involved in knee extension) during knee extension through a concurrent firing process, the greatest degree of hamstring recruitment should provide the greatest degree of protection to the knee joint. (7) When one is a powerlifter, the top surface of the legs at the hip joint must descend to a point below the top surface of the legs at the knee joint.
Knee injuries are one of the most commonly stated problems that come from squatting, however, this is usually stated by those who do not know how to squat. A properly performed squat will appropriately load the knee joint, which improves congruity by increasing the compressive forces at the knee joint. (8,(9) which improves stability, protecting the knee against shear forces. As part of a long-term exercise program, the squat, like other exercises, will lead to increased collagen turnover and hypertrophy of ligaments. (10,11) At least one study has shown that international caliber weightlifters and powerlifters experience less clinical or symptomatic arthritis. (12) Other critics of the squat have stated that it decreases the stability of the knees, yet nothing could be further from the truth. Studies have shown that the squat will increase knee stability by reducing joint laxity, as well as decrease anterior-posterior laxity and translation. (13,14) The squat is, in fact, being used as a rehabilitation exercise for many types of knee injuries, including ACL repair. (15)
1 Stance width and bar load effects on leg muscle activity during the parallel squat. McCaw ST; Melrose DR Med Sci Sports Exerc, 31(3):428-36 1999 Mar
2 Ariel, B.G., 1974. Biomechanical analysis of the knee joint during deep knee bends with a heavy load. Biomechanics. IV(1):44-52.
3 High- and low-bar squatting techniques during weight-training. Wretenberg P; Feng Y; Arborelius UP, Med Sci Sports Exerc, 28(2):218-24 1996 Feb
4 An analytical model of the knee for estimation of internal forces during exercise. Zheng N; Fleisig GS; Escamilla RF; Barrentine SW, J Biomech, 31(10):963-7 1998 Oct
5 Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises. Escamilla RF; Fleisig GS; Zheng N; Barrentine SW; Wilk KE; Andrews JR Med Sci Sports Exerc, 30(4):556-69 1998 Apr
6 A comparison of tibiofemoral joint forces and electromyographic activity during open and closed kinetic chain exercises. Wilk KE; Escamilla RF; Fleisig GS; Barrentine SW; Andrews JR; Boyd ML Am J Sports Med, 24(4):518-27 1996 Jul-Aug
7 Chandler TJ and Stone MH. (1991) The squat exercise in athletic conditioning: a review of the literature. NSCA Journal. 13(5): 58-60.
8 Hsieh, H. and P.S. Walker. 1976. Stabilizing mechanisms of the loaded and unloaded knee joint. Journal of Bone and Joint Surgery. 58A(1):87-93.
9 Uhl, T.L. and P.V. Loubert. 1990. Axial compression effect on anterior displacement of the in vivo tibeofemoral joint. Masterís thesis, University of Michigan, Ann Arbor, MI.
10 Shankman, G. 1989. Training guidelines for strengthening the injured knee: basic concepts for the strength coach. NSCA Journal. 11(4):32-42.
11 Tipton, C.M., Matthes, R.D., Maynard, J.A. and Carey, R.A. 1975. The influence of physical activity on ligaments and tendons. Medicine and Science in Sports. 7(3):165-175.
12 Herrick, R.T., Stone, M.H. and Herrick, S. 1983. Injuries in strength-power activities. Powerlifting USA. 7(5):7-9.
13 Panariello, R.A., Backus, S.I., and Parker, J.W. 1994. The effect of the squat exercise on anterior-posterior knee translation in professional football players. American Journal of Sports Medicine. 22(6):768-773.
14 Steiner, M.E., Grana, W.A., Chillag, K., and Schelberg-Karnes, E. The effect of exercise on anterior-posterior knee laxity. 1986. American Journal of Sports Medicine. 14(1): 24-29.
15 Palmitier, R.A., Kai-Nan, A., Scott, S.G., and Chao, E.Y.S. 1991. Kinetic chain exercise in knee rehabilitation. Sports Medicine. 11(6):402-413.