TweetIt is not actual muscle memory. What occurs is that when we train we stretch the fascia that surrounds the myofibral bundles(like cable bundles on a suspension bridge) that make up our skeletal muscles. That is how we grow. When the stimulus is removed for muscle growth( weight training) we shrink. But the fascia has "strtch marks" now and when we train again we seemingly grow very quickly. In fact we grow at a normal rate we just do not have the confining un-"stretched" fascia to battle with the second time around. Your growth will level off right where you left off and growth then slown and becomes more of a chore. The same holds tru for the neural pathways created and stimulated by resistance training. They are not stretched but they have been created and utilized and the body has a less difficult time re-establishing them ans using them to greates efficiency.