Join Date: Dec 2010
Location: southern Arizona
Feet are too far forward and leg has too much bend. I'd guess you have too much pressure on the stirrup and not enough weight in your heel. I'd try a longer stirrup and try to let your leg relax. Let gravity pull your leg down.
Let the horse's movement push you up. Then momentarily and in rhythm with the horse, allow tension in the legs to pause, then slow your return to the saddle. Relax and repeat.
I was taught posting as a way to avoid sitting the trot, rather than as a refinement of it. I think that was wrong. It led me to riding with constant tension in my legs, making me stiff. My horse then was stiff in response. I'm not an experienced rider and a video of my riding would give howls of laughter or bug-eyed revulsion if posted, so take it for what it is worth. It is something I've started to learn in the last few months. Riding should be a dance, not a wrestling match. When my calf-thigh angle is around 150-160 degrees instead of 130, and when I relax my legs, my heels come back and I can accept the horse's motion and use it to my advantage.