Like what longjab is saying i think most of the rebound effect in this case would be from neurological and CNS adaptions, i also remember reading an interesting study regarding the stretch in fascia's surrounding the muscle is what allows for a rapid regain after only short layoff's, after a period of time the fascias tighten back to where they where if a similair regime isnt continued shortly (maybe 6 months or so) after the lifting has stopped, and the regains due to fascia's stops. there are lots of reasons why this happens. I believe What is refered to as ''muscle memory'' comes from the heart.