I was a goalkeeper in high school and I remember endless debate among my teammates about this very subject. I ended up stressing about it so much that whenever we would practice PKs I would end up never being able to commit which way to dive.

So my coaches advice was to just pick a direction and go that way no matter what. 50% of the time I had a very good chance of blocking the goal. For me it was more mental than physical. Seems like the psychology of this one-on-one moment also deserves some good study.

I have always thought that PKs are kinda ridiculous. I mean its one thing in basketball when you get penalized by two or three points out of a hundred or so to determine a game. But in soccer, one point can pretty much determine the game. That's allot of pressure to put on one person in such a team sport....just my unscientific tangent.