It is apparently easier for someone who has done strength training or body building to get back into it then the first time around. I don't know the science behind it but I've heard it from many sources.

I don't know if muscle memory is a scientific term but I understand it as adaptations of muscle and nerves that are skill specific as a result of training. I think it's hard to put a boundary around the brain here. The brain and the nervous system is also a component of strength.