Originally Posted by
Skumbo
I'm assuming you're referring to being a person who lifted weights a lot (lets say you could squat 400 lbs) then you stop for a few years.
Assuming you never lost weight (most get a bit fat and gain some weight when they stop working out) and special circumstances withstanding (chronic conditions, really really poor diet, etc.) your body would have no reason to remove any of that muscle you had already, especially with caloric excess.
What happens is your muscles become "untrained" in the sense that you stop using many of the motor neurons/pathways that were created (your body creates more motor units) and increasing motor unit pools.
Keep in mind that your body is designed to survive, so you will automatically use as little muscle as possible while doing activities. Your body will activate the smallest motor units first, then go up the "list" so to speak. Most untrained (even trained) individuals cannot activate "all" of their muscle at once, the body just doesn't do that, but you can train it to do it more.
This is much of the reason why "untrained" individuals increase in strength so quickly in the first 4 weeks of proper training, not because they're suddenly gaining tons of muscle, but because their body is developing more motor units (to use muscle it wasn't before) and increasing how many fibres each unit recruits (increasing how much muscle can be used at once)
So back to the "muscle memory" thing. Basically, you still have most if not all of that muscle you had when you stopped, but your body isnt used to, nor does it want to use the muscle as it takes too much energy, and you've given it no reason to. So you'll quickly start getting back those motor units/pools you used to have, and begin to use all that strength again that you used to have.
Its because of this that children (preadolescent) and elderly (65+) in general have much higher muscular endurance than strength, because they havent made the motor units and that they degrade/need to be replaced over time, and many elderly don't use them so they "go away" to make you more efficient at using energy) respectively (for young and elderly).
They have more endurance cause they have the muscle, they just cant use it all *at once* like you would during a heavy set of squats.
So you haven't trained in a while, you figure out you can only squat 200 lbs (we'll pretend you have good flexibility hehe). In the next few weeks/months assuming you train and eat properly, you'll shoot up to near that old 400 lb mark because you have the muscle, you just need to get your body "used to using" all of it at once.
I can find some studies/specifics on it if you'd like.
Source: My Exercise Physiology degree I'll officially have in 3 weeks when i graduate.. also I did a whole term project reviewing this subject for my intro to ex phys class sophomore year. I should see if I still have it..