We use our backs so much in riding; we absorb the motion, we follow the
motion, and use seat/weight aids to influence the motion. The stronger
your back, the more precise your aids can be.
This is just for fun. You can compare falling from a horse standing
still, a horse running, and getting bucked off high above the horse.
(Javascript calculations)
A good mounting block is a useful tool, but they're so expensive in the catalogs. Here's a tall 3-step
mounting block that I made for less than $20, with a description of how I made it.