First of all, a squat is a compound move....all squats are going to work the posterior chain, the quads, etc. Sometimes people forget to recruit the glutes/hams for squat, and I don't think oly lifters neglect this just because they use alot of front strength...that's all I was saying. I think it's safe to say that you will always be stronger recruiting more muscles than less.
I have backed this point up many times, so doing it again will only involve pasting a pic I already have:
My point was that he STILL sits back, and his knees are not gortesquely over his toes because he possesses the hip and hamstring strength and flexibility to do it that way. It is not physiologically impossible to sit back and go low; I do it all the time...even in a wide stance (knees do not come forward, sitting back, ATF):
With a strong, tight core, and alot of practice and flexibility, this CAN be done. Most of the time when I see people squat ATF, they are in a weird forward leaning position, almost on the balls of their feet, which puts the lower back, knees, etc...in a compromised position. That is the only reason I addressed this form issue with satch. In the event that he IS doing them in this compromised position, there's no wondering why his lower back hurts.
Also, taken from Arioch's Squat Theory and Execution:
In choosing these particular quotes, I wanted to point out that even though a squat can involve more quad recruitment (especially in a narrow stance) it is obvious that RECRUITING the hips/hams to HELP the quads is safer and more productive than sacraficing the hips/hams to use the quads. Why choose, when you can use all the tools available?
I have backed this point up many times, so doing it again will only involve pasting a pic I already have:

My point was that he STILL sits back, and his knees are not gortesquely over his toes because he possesses the hip and hamstring strength and flexibility to do it that way. It is not physiologically impossible to sit back and go low; I do it all the time...even in a wide stance (knees do not come forward, sitting back, ATF):

With a strong, tight core, and alot of practice and flexibility, this CAN be done. Most of the time when I see people squat ATF, they are in a weird forward leaning position, almost on the balls of their feet, which puts the lower back, knees, etc...in a compromised position. That is the only reason I addressed this form issue with satch. In the event that he IS doing them in this compromised position, there's no wondering why his lower back hurts.
Also, taken from Arioch's Squat Theory and Execution:
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.
One of the most, if not the most critical factor in squatting is spinal position. It is incredibly important not to round the back. This can lead to problems with the lower back, and upper back as well. The back should be arched, and the scapulae retracted, to avoid injury. This position must be maintained throughout the entire lift, as rounding on the way up is even more common than rounding on the way down, and people who make this mistake are the ones who perpetuate the “squats are bad for your back” myth. Furthermore, spinal position is essential to maintaining a proper combined center of gravity (CCOG). The farther one leans forward or, even worse, rounds the back, the more strain the erectors are forced to bear, and the less the abdominals can contribute to the lift. To say nothing of the fact that the greater the lean, the greater the shearing force placed on the vertebrae. Proper spinal alignment will assist in ensuring that the majority of the force the spine must bear is compressive in nature, as it should be. Another reason for descending below parallel is that the sacrum undergoes a process known as nutation (it tilts forward, relative to the two ilia on either side of it). At only 90 degrees of knee flexion, the sacrum is still tilted backward, which inhibits proper firing of the erectors and gluteus maximus and minimus. Going through a full range of motion completes the rotation of the sacrum and allows maximal muscular recruitment.
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.
The primary muscles which contribute to the squat, in no particular order, are the quadriceps, hamstrings, hip flexors/extensors, abdominals, and spinal erectors. When an athlete fails to rise from the bottom of a squat, it is important to note that not all of the muscles are failing simultaneously. Rather, a specific muscle will fail, and the key to progress is identifying the weakness, then strengthening it. While it is impossible to simply state that if x happens when squatting, it is muscle y that is causing the problem, some general guidelines follow. If a lifter fails to rise from the bottom of a squat, it generally indicates either a weakness in the hip flexors and extensors, or a lack of acceleration due to inhibition of the golgi tendon organ (no stretch reflex – train with lighter weight and learn to accelerate if this is the case). If an athlete has a tendency to lean forward and dump the bar overhead, it generally indicates either weak hamstrings or erectors. If an athlete has trouble stabilizing the bar, or maintaining an upright posture, it is often due to a weakness in the abs.
In choosing these particular quotes, I wanted to point out that even though a squat can involve more quad recruitment (especially in a narrow stance) it is obvious that RECRUITING the hips/hams to HELP the quads is safer and more productive than sacraficing the hips/hams to use the quads. Why choose, when you can use all the tools available?