During a lesson (the only lesson I have ever taken), my instructor was having me trot (rising) the rail. Keep in mind, my personal horse was not even going under saddle and I had been riding barn horses once every few weeks, at MOST.
Anyway, she got side tracked and left me doing endless circuits of rising trot when I was SO out of shape on a horse with a flat trot, so I was doing all of the work. We probably did 15 rounds in a BIG arena.
She FINALLY came back in and asked me if I want to stop. Uhm, YES?!
I also fell in a heap on the ground when I dismounted.
"There's nothing more humbling on the planet than horses." --Sean Crocker