How does impulsion change as collection develops in dressage?

As collection develops, impulsion is not reduced but redirected — the same energy that produced ground-covering extended movement is increasingly stored and carried rather than expressed as forward progression, producing the characteristic elevated, cadenced quality of the highly collected gaits. This transformation of impulsion as collection develops is one of the most important concepts in advanced dressage training, because it explains why a correctly developed Grand Prix horse moving in piaffe — in which all the impulsion is stored in place with no forward progression at all — can be said to have more impulsion than a Training Level horse trotting forward, even though the Training Level horse is covering far more ground. The relationship between impulsion and collection is best understood through the image of a coiled spring: more energy is required to coil a spring tightly than to allow it to extend freely, and a tightly coiled spring contains more stored energy than an extended one even though the extended spring appears to be moving more. Collection essentially coils the spring of impulsion, storing more energy in each stride as the stride shortens and elevates rather than lengthens and extends. Practically, this means that developing collection requires maintaining or increasing impulsion rather than decreasing it: the common mistake of attempting collection by slowing the horse and shortening the stride through rein pressure without maintaining the hindquarter engagement produces a horse that is compressed rather than collected — slow without spring, short without elevation, restricted without carrying power. Maintaining impulsion as collection develops requires that every step of shortening and elevating be accompanied by sufficient forward energy and hindquarter engagement to ensure that the stride retains its elasticity and power even as it becomes shorter and more upward in its direction.