Quote Originally Posted by BASK8KACE
Here are some excerpts from a few places on the net:


MYTH #3: I can isolate my quads better by using a block or weight under my heels.
SHATTER THE MYTH
The practice of putting blocks or weights under your heels is widespread among bodybuilders in order to gain better isolation of the quads while squatting. The problem is that your knees go way out over your feet, placing great shear and compression on both the cartilage and ligaments of the knee, which over time can cause serious damage to the knee joint.

Above taken from: http://www.topendsports.com/fitness/technique-squat.htm

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Downward Phase

Slowly lower the body by flexing at the knees and hips. The torso is maintained in an erect position. Weight should be distributed over the middle of the foot, NOT on the balls of the feet or the heels. The heels should remain in contact with the floor at all times. Continue to lower hips until the tops of the thighs are parallel with the floor. Keep in mind that the knees should not protrude over the tips of the toes. Do not bounce at the bottom of the lift.

Above taken from: http://www.athleticadvisor.com/Weight_Room/squats.htm
In response to your argument, Several studies have shown the tensile forces on the ligaments of the knee to be minimal during any squatting movement as compared to even jogging. This also applies to the shear and compressive forces on the cartilage, and as a note, the knee is well equipped to handle these types of forces particularly in deep flexion because of the largely increased surface area of the cartilage in deep flexion. (pressure is per square inch of area). Not only that but the lateral meniscus will actually shift posteriorly (caused by action of popliteus) providing both increase surface area and stability. When jogging (single legged action creates a joint reaction force equal the 3 times body weight where as a double leg supported movement will divide the force) these forces occur with less flexion in the joint resulting in a high force with minimal surface area equaling more damage. So if your worried about damaging the cartilage and ligaments in his knees the he should especially not jog or play basketball or soccer