Bianca I would say your horse is indeed is tension with the belly muscles, but it is similar but a difference as it will be working but not tense the muscle should never be tense as that causes discomfort, it does in us when we are tense as i am sure it does in animals too, so another key is to get the muscles working they have to be toned not tense looking.
I have a great picture of them being used it is of one of Heather Moffett's horses but would you be ok with it as it is bitted but does demonstrate the muscle being used wonderfully for this purpose
Miriam I see their point but I inclined to disagree slightly that
They told that the belly is full of soft tissue with horses that is hanging down: The horse just isnt able to lift his back by pulling together his bellymuscles as all that would do is squeeze his intestines
This is same in us humans our muscles are outside of our intestines too so we do squeeze ours as well so to me that doesn't stand very well.
As all the muscles are connected the back muscles will be connected to the stomach muscles they work best when they are all working together and if we can train the horse to do this it will help their back, I am going to go back us humans again ok we stand up on two legs but when we build our stomach muscles up and get them working our back muscle will be more protected and stronger from working together with the back muscles.
So what I was saying it is just as important to make sure the stomach is connected while working the horse to raise it its back as if it is it would allow a better movement and freer movement from the back.
I agree that the horses do have use the belly muscles to help draw the legs under more when galloping with Race horses but RHs do have poor backs, part is from having too much weight on their backs at a young age but also that they will and are trained to use their stomach muscle more than their back muscles, hence why they have back problems but tighter belly muscles.
So what I am saying both have to work together more or less equally in harmony not one is better than the other as you still end up with back problems or a better back but a belly that still sags. Now learning how we can get a horse to do this is a good question and it is maybe in the way we work the back by getting the hind leg to step under int he exercises we do with them that this happends naturally.
Another interesting thing that scientists have found out is that horses dont bend their ribcage and loins around the inside leg in curves and for example shoulder-in as we have always been taught, but instead rotate their spine towards the outside a little and by that lifting the inner ribcage-half out of the way of the inside hindleg - without actually bending the spine even though it looks like that because the inner ribcage half seems to bend away.
Yep they do indeed lift their rib cage, as I have known since my Alexander techinque teacher, (reiki, kinesiology, bowen therapist) said about going round on a circle think of it as if you are trying to lift the rib cage outwards, so the inside will come under and the outside will lift out further enabling the hind leg to come under easier.But is different movement to the SI.
With the SI it works the same way on us too if we mimic it, it does do all that is said by Miriam
But going on a circle is slightly different to SI as they you don't always do SI on a circle and well my horse doesn't but does lift her rib cage outwards to the outside though.
Windhorsesue to regard about your posture I feel another thread coming on
But that is basically as the muscles are doing what has come naturally to them over time and this all changes when we learn how to connect to our core which BTW is not just our stomach muscles as they do attach to the spine as well this is why getting the core working helps our backs