Just my opinion. Apologies for the typos in my post- however what I said holds true. Box squats are a TERRIBLE exercise that should not be attempted by anyone. In order for any athlete to progress, you need to create a periodised training program, which alternates training intensity and variety. I'm sure these guys have great squats, due to super human hard work, dedication nutrition and genetics - however I'm not convinced about a lot of the advice here. Good mornings may be beneficial, but doing so many is another sure-fire way to damage yourself. This is training advice for a highly advanced athlete- if you are not close to squatting insane numbers, you should under no circumstances consider box squats and lots of good mornings (deadlifts should be the mainstay of back development). The author does not emphasise that you should build up from low intensities to high over a period of say 12 weeks, before transitioning to another phase of training. By "jumping straight in" with high stress movements you are asking for trouble, especially if you are new to said movements.
I may not be as an accomplished squatter as the autor, but I can still squat 240kg at a weight of 82kg. Without trying to sound self important, I can also say that I have a first class degree in Sport Science and a masters, so I do know what I'm talking about. I felt it important to give a different view, because I can see someone doing ultra heavy spine-loading exercises without care and attention. Good luck all!