Following the movement is not a feeling you can summon by trying. It's a set of things your body does, and once you understand what those things are, you can build them.
When researchers measure how skilled riders coordinate with the horse, one finding comes up again and again: the pelvis is tightly coupled to the horse - it matches the movement closely - while the body above, the head and the feet are far more loosely coupled, free to do something other than what the pelvis is doing (Wilkins et al. 2022). That separation is dissociation. Following is the pelvis moving with the horse while the rest of you doesn't.
The difference timing makes
What separates a developing seat from a deep one? When researchers compare the muscle activity of less experienced and more experienced riders, they find two different strategies. The less experienced rider tends to tense the muscles on both sides of the body, switch on together and hold, a kind of all-on, all-off stiffness that grips and braces. The more experienced rider's body works in a finer pattern: one side switches on as the other releases, in time with the horse, so the seat follows the movement rather than clamping it.
That shift - from bracing both sides at once to a co-ordinated give-and-take timed to the horse - is a large part of what we mean by an independent seat. The timed, side-to-side coordination keeps refining for as long as you ride, getting quicker, finer and more automatic.
Why following needs movement, not stillness
This is worth saying clearly because the language of riding works against it. We tell riders to "sit still," "be quiet," "stop moving about." But the skilled seat is not still. The research is consistent: the pelvis of a skilled rider moves more than a beginner's, not less. Münz and colleagues (2014) measured over 11° of pelvic pitch in professional riders at sitting trot, against around 8° in beginners.
What's still is the body above. The head. The hands carrying the contact. The pelvis underneath is working hard. When a rider looks still and quiet on a horse, what you're seeing is a busy pelvis under a calm upper body. The stillness is in the wrong place to be the goal - it's a result of the pelvis doing its job so well that nothing above it has to react.
The role of tone
Following is not floppy. As I said in Phase 1, "just relax" is as unhelpful as "sit still," because tone and control are needed in different amounts at different moments. The pelvis follows with a certain softness, but the body above holds with a certain tone, and the amount of each shifts constantly as the horse moves. A rider who goes completely loose collapses. A rider who braces everywhere blocks. The seat lives in between, and it's a moving target, not a fixed setting.