You post when the horse enters a trot. You use your legs to control your own up and down motion, basically going up and down once for every time the horse would make you go up and down. when you do this, the motion is fluid. You're still going up and down, but you control your motion with your legs. You don't do this when the the horse is cantering or galloping (the two faster speeds--think of how thoroughbred jockeys ride). If you don't post in a trot, you bounce all over the place and seriously numb your a$$. It's also easier on the horse.

It's not the same motion exactly, but that's why Mr. Brown put the word in quotes I guess. You have to control your leg motion to control your body while moving to not get saddle sore--makes sense.

ps--I was never good at riding horses, and I'm sure that someone here knows better than I do. but I actually knew something relavent to the topic and couldn't help myself.

continue on with the sexual deviancy and animal rights.