This has been a huge problem with me and I've mentioned it on other threads but I thought I'd post here to see if I could get some more exercises.
Regardless of how relaxed I feel, I carry a lot of tension through my lower back and tend to push my butt out and have a exaggerated curve in my back.
Here's some old but relevant photos. My other weak point is my shoulders which weakens my elbows (Im a mess, I know) and I have been working on that. I think in the last few lessons I have made a lot of progress with them, but I havent had anyone to take any photos yet.:
I have been riding western at home for the past week and noticed I didn't have the same problem (I have been primarily a western rider up until the past year)
So. I've been riding without stirrups a lot. As well as bareback. I've been trying to do some exercises off the horse with strengthening my upper back (the muscle group between your shoulder blades?) as well as some work on an exercise ball to try and strengthen my core (and thus in theory release the tension in my lower back)
But does anyone have any other suggestions? This and my elbows are my two biggest problem areas. My elbows I can at least get to function for about half a lesson or so but my back seems to be useless...