I think the problem is the events of the world youth championship. Out of eight events, you have 100m, 400m, 1000m, 110m hurdles which are all running evets. So 50% of the events are running, and if you are a good runner, you are probably good at the long jump too. You don't you to be as all-round in the octahtlon as you have to be in the decathlon.