In a recent release, world renowned strength coach Mike Boyle said that he has pulled conventional squating from his program entirely! Here's the link: http://www.functionalstrengthcoach3.com/squats.html
His reasoning is that, in squating, the weakest link in the kinetic chain is the lower back. He states that to better work the legs, you must switch to single leg supported squats. By switching to single leg supported squats, it takes the entire core out of the picture.
I agree with MOST of what Coach Boyle puts out. However, I think he is being a little extreme here. Here is my take on the subject:
I think that single leg movements are a very essential part of every well rounded strength training program. I personally incorporate multi - planer lunges and step ups in every program I write. However, I WILL NOT remove the conventional squat and other types of squats from my programs.
The reason for this is simple. As strength coaches and trainers, it is our responsibility to get the athlete or client to transfer as much force as possible from the ground up. His example is a freshman who did a single leg supported squat (SLSS) with 115 pounds for 15 reps. His argument was that since the athlete was not able to perform the back squat with both legs with 230 pounds for 15 reps, the single leg supported squat is superior to the conventional back squat.
If you look at the back squat as just a lower body exercise, then I would say you are correct. But, here's the problem. It's not just a lower body exercise. Let's break this down a little bit. We'll look at it as two separate muscular systems (I know they all work together but just follow me here). You have the lower body muscles (legs), and you have the torso musculature (core). Let's remember that WORK = FORCE X DISTANCE.
So, for lower body work, SLSS results in greater work for the lower body muscles but less work for the core muscles. Inversely, the back squat will lessen the work on the legs but increase the work load for the the core. So here's what I'm trying to say:
Conventional Squat - Good lower body exercise but great for core strengthening and power transfer
Single Leg Exercises - Great lower body exercise but not as great for core strengthening and power transfer
So, in conclusion, my opinion is that you should squat (any variation: front, zercher, etc) at least once per week and do single leg exercises at least once per week because
STRONGER LEGS + STRONGER CORE = STRONGER YOU!!!