I shorten my stirrups five holes when I’m jumping 1.10m and up because my horse is a big rubber ball and that works best for both of us. I can jump him with no stirrups at all or in a bareback pad, so the length isn’t what is keeping me in the saddle or anything, but it’s simply easier on his back if my stirrups are shorter. It depends on the horse and the rider and what is most effective for them. I don’t go around peering at other people’s stirrup length; I care about what works for me and that’s it.
I agree that it’s not useful to always flat in one length and jump in another, but the benefit of usually flatting with longer stirrups is exactly as has been said, which is that you get more leg real estate on the horse, making it easier to do lateral work and such. Every one of my eventer friends has a dressage saddle and a jumping saddle, and my trainers also have XC saddles that are different from their stadium saddles (much more forward flap, billets set back farther, for example) for some of their UL horses. They all seem to handle multiple stirrup lengths and saddle styles just fine!
So, it seems to make sense that if your horse isn’t responding to your aids with shorter stirrups your flatwork probably needs improvement. If I’m jumping big I flat and begin jumping with my longer stirrups until the fences go up and then I shorten them, again for his back. If there is a big shift in how the horse goes when one does that one simply has to figure out where the holes are (core strength, effectiveness of seat, balance, etc.), and work to get rid of them. If your horse jumps sort of flat, or you never jump over bigger fences then there probably isn’t much point in changing the length. But again, it all depends on what works best for that horse and rider combination.
Someone else mentioned the idea that perfect dressage isn’t going to produce perfect jumping. That is absolutely true, but it’s an essential part of it for most pairs at the higher levels, I think. Jumping is flatwork with jumps. If you watch the best jumper riders in the world their horses are going around beautifully connected, responsive to the aids, able to go from a gallop to a much shorter stride without losing balance in the blink of an eye, and so on. How do you think those tools are developed in the first place?
My wonderful trainer who passed away a couple of years ago was an incredible dressage instructor, and he always used to say that my flatwork didn’t need to be perfect like the dressage or eventer people, since I don’t usually compete in that ring. Sometimes we do a CT or a dressage schooling show, although I’m terrible at remembering the tests. He said that my flatwork DID have to be effective, though, because when the jumps go up and the questions get harder the holes in the flatwork will be very apparent. Up to 1.10m with my current horse I was able to get away with having those holes because my horse is a stellar athlete, but moving up to 1.20m they became problems I had to fix for us to be competitive.
It’s a way of thinking about riding more holistically that has really helped me, especially with this particular horse, but again, everyone has different approaches!
[ETA: I am sorry for the novella. I’m getting ready for a new semester so of course this is more entertaining than writing a syllabus! I’ll get back to work now…
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