The way to improve from one level of fitness to the next is by working harder. There is no substitute. There is no shortcut. Hard work is the way it happens. No matter how much talent a person has been born or blessed with, talent alone is not sufficient for continued and sustained success.
Hard work is always necessary.
Sports science exists to determine exactly what kind and how much hard work is required, and when. In the athletic world, not playing by the rules makes no sense whatsoever. It is nonsense because it is not comprehensible. When swimmers race 100 meters, they race 100 meters. That is the race.