UPDATED - My lower back gets tired from doing 2-point:
This post is somewhat related to one I created recently around building flexibility in my body and strength in my core.
Over the last few 1-2 months, I'm feeling much better about my ability to have a strong leg position without getting tired. The stretching and tightness I used to feel in my legs and hamstrings is now almost a thing of the past. Yay!!
The next thing I need to work on is my lower back. I can ride until I'm blue in the face in my dressage tack with almost no problem. I can do the same in my jump tack. I can do gymnastic exercises, do courses, etc. almost indefinitely if I'm trotting in. However, when doing exercises at a canter in 2-point like the "circle of death", I know I have a certain amount of loops I can do before my back gets tight and I need to take a break. It's not that I can't continue because I can. What happens is when I start to get tired my lower back gets tight and my sensitive mare feels it and starts to fuss a bit. I usually find that a walk break helps immensely.
I'd like to build up my endurance so I can go a full lesson (~1 hour or so) without having to take breaks or get tight in my lower back.
What would be the most effective way of strengthening my lower back so it doesn't get tight when I'm spending a lot of time in 2-point? I think part of what I'm feeling is residual fatigue from some very intense private pilates classes I've taken recently. I think I have to back off on those and just do 15-20 min. on my own per day to start.
What exercises would be good for helping my lower back stay supple and not get so tired in 2-point?