I take hunt seat lessons (taking formal lessons for the first time in several years), and I also trail ride with a lady who does endurance.
My major problem during lessons is leg position. My hips and ankles are not flexible, so I tended to adopt the classic chair seat. Some stretching and a detail-oriented instructor seems to have corrected this problem. At my last lesson a bit of two point at the trot got my leg into the right place and I had no problems with my legs or stirrups after that.
However, when I trail ride I ride in a dressage-type Wintec with longer stirrups. I have a bad ankle that starts killing me after an hour or so in stirrups of any length, so shortening the stirrups more isn't an option. We go on very long rides, sometimes three hours plus.
My issue is that when I ride with longer stirrups, I have a terrible time keeping my stirrups at a posting trot. I feel like I can't keep my heel down far enough to put weight in my feet. After a while I just sort of stop using my stirrups much at all, and they swing around between my heel and toe. Although I don't usually lose them completely, I feel like I could drop them both and wouldn't feel much of a difference. It doens't make me feel unbalanced but it's annoying and I can feel that my leg is moving around too much, and I start coming down a bit hard on his back.
Part of the problem is that the horse I ride is Big and fast (was a 4th level dressage horse in his previous career...now likes to race down the trail ). Also I'm still not in super good shape, having only been riding for a month after a year off, so my legs get somewhat fatigued on our long rides. The stirrups tend to get progressively worse throughout the rides. But are there any thoughts on something specific that might be causing the issue? Is there something I can work on or do I just have to keep riding and it will resolve itself as I get in better shape? I've considered just trotting him in a half seat to keep my weight in the stirrups, but I'm not in good enough shape to hold that for the amount of trotting we do sometimes. Let me know if you have any thoughts...