Re: What are the 9 Foundational Movements?
These movements were chosen because they are universal motor recruitment patterns. First, they are a progression on each other, that I won't explain since Frederic did such a good job. Bottom line is that you can't clean until you can Dead lift and front squat. As far as the pressing movements being the same with different levels of hip involvement, think of each one in the progression as a more efficient means to the same end as the one before. The most efficient way (and maybe the only way by proxy of the size of the object to be lifted) to get something from chest to overhead is the Push Jerk, and putting things overhead for one reason or another is important.
I said that these movements are universal motor recruitment patterns. Basically what that means is that if you desire to get better at things that involve the human body, you need to do these things well. If you want to jump high or far, you need to squat, clean and dead lift. If you want to run fast... same. As far as the over head stuff goes, they illicit some of the strongest contractions of the core and require enormous amounts of midline stabilization. That translates to all of sport.
The Sumo Dead Lift High Pull: This movement is a precursor to the clean. It teaches proper kinetic chain when taking something from the ground to the chest. It is also a more functional version of the clean (in a manner of speaking, I know there is no drop under or third pull). Think about it like this: if your buddy gets shot in the streets of Iraq are you going to run him through with a bar so you can clean him up to your shoulder, or are you going to straddle him with your hands inside of your feet, violently extend your hips and then drop under him?