Heya...I'm not any huge expert but i can relay a little wisdom from a guy i know who is.
He reckons muscle has fantastic "memory." Once u develop a muscle to an extent once, (and then let it slip so to speak) it is a lot easier to rebuild that muscle in comparison to when you first achieved such condition. However he also believes that once u reach ur thirties it becomes much more important to maintain constant condition as once u slip the opposite happens and it becomes considerably harder as the body depreciates in condition.