New physical challenges?

As a child, your life is replete with physical challenges. For example, learning how to sit, then learning how to stand, then learning to walk, learning to balance, and traversing uneven terrain.

However once you become an adult, it seems that no more physical challenges exist.

Perhaps why the ancient Greeks and the ancient Spartans were so into combat, battle and war, is because there is a primal joy of physical challenges and conquest?