Explain the sitting trot and how to do it?

The sitting trot — remaining in the saddle through both beats of the trot's two-beat diagonal rhythm rather than rising with one beat — is one of the most technically demanding basic riding skills and the one that most clearly reveals the quality of the rider's seat and the degree to which the rider can follow the horse's movement rather than resisting it. The trot's diagonal footfall creates a vertical thrust upward into the rider's seat with every stride that must be absorbed through the rider's own body, and the body that can absorb this thrust correctly — through a relaxed lower back, following hip, and independent leg — sits the trot beautifully. The body that cannot bounces. The foundational principle of the sitting trot is that the rider follows the horse rather than the horse accommodating the rider. The horse's back at the trot swings up and forward with each stride, and the rider's seat must follow that swing rather than sitting rigidly and allowing the horse's movement to bounce the rider off the saddle. Following requires a lower back that is neither braced and hollow nor collapsed and slumped, but softly upright with enough mobility to absorb the trot's vertical thrust into the lumbar region rather than transmitting it upward through a rigid spine. The hip joint is the primary shock absorber in the sitting trot, and its mobility determines the quality of the sitting trot more directly than any other single physical factor. A hip that is tight and restricted — held closed by gripping inner thigh muscles or a braced lower back — cannot follow the horse's movement. A hip that is open and mobile can absorb the trot's thrust and follow the horse's back through its full range of swing. The specific physical correction that unlocks the sitting trot for most struggling riders is releasing the inner thigh. The inner thigh that is gripping the saddle creates a rotational force on the femur that tips the pelvis forward, tightens the lower back, and closes the hip joint in exactly the position that prevents following the movement. When the inner thigh is released and allowed to lie passively against the saddle, the pelvis drops back and down, the lower back softens, and the hip opens enough to begin following the movement. Building the sitting trot progressively — beginning with very short intervals of five to ten strides within longer periods of posting trot, increasing the duration only as each interval becomes genuinely comfortable — develops the specific muscular endurance that sustained sitting trot requires. Longe line work without stirrups is the most efficient tool for developing the sitting trot seat and should be used without hesitation by any rider who wants to genuinely improve this skill.