Page "Stirrup" Paragraph 35

While an inexperienced rider may feel more secure with a slightly too-short stirrup, in reality, it is actually easier to be thrown from the horse because the rider's legs act as a stabilizing agent, much in the same way the long pole of a tightrope walker balances the acrobat.

Obviously, a stirrup leather so long that a rider cannot reach it is useless, and a stirrup length that does not allow a rider with a properly positioned leg to keep the heel lower than the toe is also easily lost.

However, shortening the stirrup until the rider feels they will not lose the stirrup is counterproductive ; the goal of correct equestrianism is to make maximum use of the leg.

Lengthening the leg creates a more secure seat, while shortening the stirrup is done only to accommodate the needs of the horse to perform athletic movement.

Thus correct stirrup length creates a balance between control and mobility that fits the discipline performed.