Collection is also essential in jumping. Most horses will physically be unable to jump extremely high fences (such as those seen in Grand Prix show jumping or puissance classes) without collection, as they will not have enough power to make it over the obstacle. Speed is not a substitute, and a horse that is simply galloped at a fence will find it extremely difficult to raise his forehand upward on takeoff and gain enough height over the fence. Instead, he will jump flat, without bascule, and will be much more likely to pull a rail. Secondly, horses must be adjustable within jumping courses, having the ability to shorten or lengthen their stride between obstacles, especially if placed in a combination. A horse that is not collected will find it very hard to seamlessly shorten his stride in a related distance, and may be forced to take off too close or too far away from the jump, which greatly increases the chance he will hit it.