Final answer:
World-class ski jumpers are often ectomorphs because their tall and slim physique allows for better aerodynamics and lighter weight, which improves their performance and reduces injury risk.
Step-by-step explanation:
The reason many world-class ski jumpers are ectomorphs, who are typically tall and slim, relates to the demands of the sport which favor athletes with a certain body composition. Ski jumping requires athletes to maintain a careful balance between weight and aerodynamic efficiency, and being tall and slim helps reduce air resistance while still allowing for a substantial surface area for lift. Additionally, a lighter body weight can result in less force upon landing, which is beneficial in terms of reducing the risk of injury. Like other sports that demand specific body types for optimal performance, such as dancers and gymnasts facing the pressure to be thin, or sprinters benefiting from a powerful muscular build, ski jumping is no different. In ski jumping, the physique of an ectomorph is advantageous. Cultivating the optimal body composition includes considerations of energy intake and other forms of manipulation, but it is recognized there is no single "optimal" body composition that suits all athletes in all sports.