Please explain it to me then, because this is what I know to be true...based on biomechanics and experience:
Stance. This varies from individual to individual, but one thing is necessary for all who wish progress: you must keep your feet flat on the deck at all times. The center of gravity may be maintained over the center of the foot, but it is generally best to push through the heels. This will help in maintaining bar position and help eliminate a small degree of forward lean. To achieve this, some people find it necessary to curls the toes upward while squatting, forcing their heels flat. The feet should be placed at least shoulder width apart, and some individuals may best utilize a stance nearly twice shoulder width. The narrower stance tends to place more direct emphasis on the quads, and creates a longer path for the bar to travel. The wider stance (often called “sumo”) tends to be favored by many powerlifters, although some have enjoyed great success with a relatively narrow stance. The sumo stance place more emphasis on the adductors and hamstrings. As a rule of thumb, lifters with longer legs will need a wider stance than shorter individuals. However, there are exceptions. A wider stance will tend to recruit both the adductors and buttocks to a greater degree than a narrow stance. (1)
The shins should be a close to vertical as possible throughout the entire movement. This lessens the opening of the knee joint, and reduces the shearing force as well. By reducing the workload that the knee joint is required to handle, more of the work is accomplished by the larger muscles around the hip joint. For powerlifters, this decreases the distance one must travel with the bar, as the further the knee moves forward, the lower the hips must descend to break parallel.
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.
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