alt Hacker News“ However, when looking at muscle, once you have it you don't need to use it as much in order to maintain it”
No.. this depends on how much muscle you have. The appropriate comparison is mass and density of knowledge/understanding vs muscle. There’s not a chance in hell you will retain mass and dense muscle without pushing the body hard. Just in the same way you will not retain very deep understanding of things unless a) you’ve been reciting it for over 10 yrs b) you go back and push the understanding continuously for it to remain as part of your being
Building muscle is much harder than maintaining muscle.
And if you went 3 years without exercising, you'll be able to get your muscles back much quicker than had you never had the muscle before.
It's pretty comparable to skills. You don't need to practice as hard to maintain a skill than you do to build it. And if you let the skill atrophy, it's much easier to recover the skill compared to building it from scratch.