Basically, I'm wondering if there's anything I can do to improve Lacey's underline. As it is, she has a rather weak back-loin area and I'd like to improve it however possible. I know she's conformationally predisposed to be weak through the back but I'm sure it can be improved upon, at least a little... She's currently working pretty hard for a horse her age, all three gaits 3-4 times a week, for about 1 1/2 hours each session, plus monthly 4 hour trail rides at all 4 gaits (galloping included). We're doing more trotting than anything right now since I'm teaching her to jog and because I have a hard time with her trot, therefore, I need more practice with it!
Here's a picture to give you an idea of what I have to work with: