- You can see that his head doesn’t really move vertically that much. He could probably get his head/feet that high without running.
- The running helps him get his body over his feet once he hooks them on the edge of the box, it doesn’t really help him jump higher.
If you are working on box jumps, you can get a lot higher by concentrating on tucking your feet under you. If you are trying to jump higher than say… the middle of your body, some horizontal movement will help get your body back over your feet once your feet land.
I’m nowhere near an expert, but watching that video and trying those things has made it so this fat boy can get onto a 38" box with a standing box jump.