This has been a constant problem for me lately and I'm hoping you guys can give me some tips here.
When I was about 10 or 11 I took a fall from a 16hh horse flat on my back and it screwed something up big time. A trainer had failed to double check my equipment and the stirrup bar on the saddle was bent and the saddle was prone to the leather sliding off...and when it did I went flopping off the side. Ever since then my back has been very weak.
Especially at a posting trot, after a few minutes I get a tight, nasty cramp in my lower back. Feels like the muscles are just in a ball. It makes me very prone to hunching and leaning because it literally feels like I don't have to strength to be upright. This stinks up my ride being that my horse is very sensitive to her rider's position and I have difficulty slowing my post when she gets quick and choppy due to my hunching.
Anyone have any tips to help keep my back from cramping, and to help me sit up straighter and keep my shoulders back? My leg/heels are apparently great. I've been getting a lot of compliments on them from my trainer and some other riders lately. The upper body just needs work.
I also have a tendency to get stiff trying to hold myself in a "perfect" position.
It's very frustrating to have stiffness and muscle cramps hold me back. I'd love to get back to jumping but I really need to get a more secure upper body. Amber is pretty bored with flat work as well! But the flat work has to be good before we do any fences.
ETA: Oddly enough, I have a much easier time at the canter and my trainer hasn't really had any major criticism for us there. It's the trot!