Assisted by a mini-skeleton he calls Mr. Thrifty who “has seen better days” Mark Rippetoe discusses the importance of the squat and the hamstring. This footage is taken from a Basic Barbell Certification Seminar held on February 14, 2009 at CrossFit Brand X in Ramona, CA.
Proper squats accomplish the exercise objective of moving more muscle over a greater range of motion, allowing athletes to lift more weight and get stronger. Hip drive engages the posterior chain. Correct stance and bar placement are essential. In the low bar back squat, the back angle is much more horizontal than in the front squat. The only way to do a front squat is with an almost vertical back.
The hamstring crosses two joints and serves two functions: knee flexion and hip extension. If the hamstring is already in a short position at the bottom of a squat, it cannot be a major contributor to further hip extension. But a more horizontal back and opening the knee will further stretch out the hamstring. The distance over which the hamstring can contract will be increased, provided squat requirements are met. The lumbar spine must stay in extension and the pelvis must stay locked with the lumbar spine.