W
Warik
Guest
Cornholio said:
Warik - can you explain why smith squats are worse for the knees than free weight squats?
From Charles Poliquin's The Poliquin Principles pg. 72
In regard to machines that attempt to duplicate the Squat, the basic problem is that many of them can reduce the pressure on the back and place significant stress on the knees. Take for example the ever-popular Smith machine. The Smith bar makes it possible to squat in a manner that allows you to lean back against the barbell, thereby supporting your back and minimizing hip extension during the exercise. What this does is take the hamstrings out of the movement. The hamstrings, however, are the muscle group that helps stabilize the kneecap. The result is unnaturally high shearing forces that try to pull the joint apart, as well as tremendous stress on the anterior cruciate ligament (ACL), one of the primary ligaments in the knee capsule that provides stability to the knee. For this reason, I would discourage you from using the Smith machine, or at least only use it on an infrequent basis.
The illustration on the left shows the shearing forces placed on the knee during a Smith machine squat. These are caused by the lack of involvement of the hamstrings. The illustration on the right shows how the force dissipates throughout the lower leg when performing a Squat.
-Warik