OK, this may get a bit technical.
I try (and often fail) to stay in a true Forward Seat ala Littauer in various of his books, riding on the flat. I have MS and I can no longer jump and canters/gallops are simply too exhausting for my body whether in 2-point, 3-point, or sitting back in the saddle. I ride mostly at the walk with some slow (I ride elderly lesson horses) trotting, sometimes extending the trot.
The leg aid I will be referring too is what I now call the “collecting leg aid.” When the horse’s barrel tries to push my lower leg out I just mostly stiffen my lower leg and resist. Sometimes I add a tiny bit of spur, just to tell the horse that this IS an aid I expect some type of response to.
When I use this collecting leg aid I and my riding teacher have noticed that my weight shifts back a little bit, I sit up straighter to completely straight, while the horse keeps its back more relaxed than tense. Since I do not do this for very long I keep my stirrups at their normal length (short enough so I can get my seat completely out of the saddle), if I was expecting to use it more I would lengthen my stirrups one-two holes. I ride in a Pegasus Butterfly Claudia jumping saddle, the one the saddler was closest to my favorite saddle, my Crosby PDN.
On one mare, elderly Arabian, I felt like a hand was on my belly pushing me back. This particular feeling has also come from the other horses I use this aid on though not as strong. When I “feel” this there is no way that I can keep in a 3-point seat, I have to relax back and end up in something that somewhat resembles a dressage rider sitting upright. The horse’s back no longer supports my 2-point, it is really hard to keep in 3-point since I feel like the back of the saddle has moved further down under my seat bones. I breathe and let the horse dictate the position of my upper body because I know if they don’t like it they will tell me quickly and sometimes emphatically. I still use my very relaxed hands in the Forward Seat methods–giving and taking and not blocking the motion of the horse.
Very rarely, usually when my hands do not give as much as the horse desires, I get some more advanced movements, the elderly Arab mare gave me a terre-a-terre one day when I was trying to canter her, and one day she gave me a croupade, both witnessed by other people. One time I got a “school trot” as described by Nuno Oliveira, that was on an Arabian gelding. Personally I consider all of these as mistakes caused by my imperfect riding though my riding teacher was impressed by how the horse moved then. I most certainly did not plan these movements, the horses volunteered them, and remained CALM.
So I see and feel the difference between the Forward Seat when the horse goes faster or is obeying one of my aids, all the while keeping his back suitable for my FS, and the weight further back, sitting on my seatbones with my body at a 90 degree angle to the horse’s back, usually when the horse slows down while shortening the stride of his hind legs with his hind legs supporting more of our weight. This happens maybe a few minutes during my half hour ride, when the horse feels like he is ready for the added physical challenge.
My contact now is ALWAYS light, with loose,supple fingers UNLESS the horse goes faster with a lot of impulse. I let the HORSE dictate the position of his head, his neck, his back, and how he moves his legs in detail, I concentrate on not blocking the horse’s forward movement. When I give a rein aid I only give it when I do not feet the hind leg on that side pushing (which means I have to give 2 hand aids to halt or slow down.) I tweak my finger, moving it maybe 1/8" to 1/4" with an immediate release and my release is GENEROUS, with my fingers relaxed and my hands moving forward a little.
I tend to avoid the sitting trot, I’ll do 3 to 6 strides then my body objects. I have a damaged spinal cord and a damaged brain from my case of Multiple Sclerosis and I am convinced that sitting the trot ends up with my brain bouncing off of my skull. I don’t want more damage to my brain so I limit the sitting trot to short, occasional sitting trots. Too protect my brain and spinal cord I also avoid bouncing on the horse’s back at the trot and canter, the bouncier the sitting trot the more likely I am to end up in 2-point to save my nervous system.
I NEVER dig my seatbones into the saddle. I do my best not to bounce at the sitting trot and usually I succeed in keeping my seatbones glued to the saddle moving them in response to the horse’s swinging back, whether in 3-point or riding the more dressage position.
I tell every horse I ride that I will go ahead and fall off rather than pull strongly on their mouth. Fortunately I ride well enough so that has not been necessary.
Occasionally, on a particularly resistant horse, I will set my hands, not move my hands, keep my fingers and arms tense, all while I wait for the horse to stop pushing as much with his hind legs. When the push is less strong I release my hand aid and reward with praise. Eventually I even got the “rebel without a cause” sour tempered ruined horse who never had a day of proper training in his life to go from me using all the muscles of my arm to keep my hand in one place to get him to slow down a little bit to being able to stop him with twiddles of my little fingers. Of course during this long process that horse did open his mouth and my riding teacher could see it since I do not ride with a noseband at all (I cut off the chin straps of my Micklem bridles so the horses can open their mouths if they need to.)
I am not gloriously galloping cross country and jumping fences in stride, but at least I did it in my youth before I got crippled (jumping 3’6").
My riding teachers LIKE how their lesson horses move under me. My riding teachers LIKE how I can change an iron jawed horse into one with a soft, responsive mouth. They LIKE seeing their lesson horses walk faster than 2-2 1/2 MPH, I always try to get to 4 MPH, striding freely on contact. My riding teachers like how I do not abuse the horse’s mouth, back or sides. My riding teachers do have to help me keep my lower leg in position, I am not a perfect rider after all.