Standing in the stirrups.
Stirrups stay steady due to gravity. If we put weight in the stirrup while our center of gravity is directly above the stirrup, then they are even steadier. If they move around, then our weight must not be above them, but either behind or ahead. If the stirrup is below your center of gravity, the only direction you can push it is down - and the saddle won't allow that!
The exception is if we grip with our knees. Then our knees, gripping in one position of the saddle, allow our lower leg to pivot around regardless of where our weight is centered.
Standing in the stirrups teaches two things: To adjust your body's position to stay balanced above the stirrup, and no gripping with the knee. Three things, because you also have to learn to anticipate balance & momentum changes by your horse and how to compensate for them.
No stirrup work, which is widely praised, teaches the opposite. Without a stirrup, the lower leg can't do much to help or harm you, and we learn to ride from the knee up: thighs and seat. Xenophon famously wrote "When mounted, the rider should sit on the horse not as if he were sitting in a chair, but as if he were standing with his legs apart.
" People then say that means keeping a vertical line from ear - shoulder - hip - heel. They talk about how, if your horse disappeared, would you land on your feet.
Please understand: I'm a self-taught backyard rider. Not a judge, instructor, and certainly not a prize-winning anything. But a horse moves around, not always because we asked him to and not always as we anticipate. I think of it more like riding a surfboard:
If you want to stay stable on a shifting surface, you crouch and try to stay above your feet. Good stirrup work on a horse is similar. Of course, many approaches to riding emphasize seat instead of stirrups. And a person may NEED to ride an excited horse without stirrups, so both need to be practiced. But our best position when using
stirrups is to stay above them.
Xenophon didn't have stirrups, but stirrups make what he taught even more effective. I would rephrase it as "When mounted, the rider should sit on the horse not as if he were sitting in a chair, but as if he were standing in the stirrups with his legs apart.
" Please take this advice with a big steaming cup of FWIW because I'm a backyard rider of Craigslist horses. I will say this has worked well for me when riding spooky Craigslist horses. But I'm no instructor.