There was a recent study somewhere that talked about how they'd cracked the code on muscle memory.

We've known for a long time that it's way easier to regain muscle than it is to develop it in the first place.

Turns out the reason is pretty simple, muscle cells are similar to fat cells - meaning that they never go away. They just activate as needed.

So it takes enormous effort to develop muscle cells, but one you have them, getting the size and strength back after taking a break is way easier.