Comment 1:
Completely useless junk science..... absolutely no correlation to how the hoof works when actually attached to a live horse. Worthless.....

Answer 1:
It's simple physics. The coffin bone is loaded at the natural pressure point and when it stands only on the outer edge this is what might happen. If the coffin bone is supported under the middle it can't happen. More common than breaking is deforming. I show and explain how that comes on my seminars.
/Ove

Comment 2:
ummm one: shoe is NOT nailed on. two: they are pushing longer on the "shoed" foot. So...

Answer 2:
One: The shoe is not nailed on but that doesn't change anything in regards to peripheral loading. Peripheral loading means that the hoof only has support under the outer edge and no support under the middle parts. This can be created by a high hoof wall and/or a shoe.

Two: Exactly the same force was used to load the hoof in both video clips. The hoof standing on the shoe does become more deformed because it is only supported under the outer edge (i.e. peripheral load). The frog doesn't stop the down going movement by becoming weight bearing as on the hoof that is standing directly on the ground. When the frog becomes weight bearing the hoof is no longer peripherally loaded which will change the directions of the weight bearing forces.

This is simple High School physics!

A shoe is not necessary to create peripheral load but in this particular case I believe it was the shoe that was the reason for the coffin bone to break.
I'd be happy to show you exactly what forces did break the coffin bone in the video clip if you would come to a seminar.
/Ove