Muscle Memory: Why is it easier to get into shape the second time
Muscles are smarter than you think, at least in one sense. They have memory, which is a good thing if you're an avid weight lifter and have to take a break from training for a few months. Because of the ability of your muscles to "remember," getting strength and muscle definition back won't take as long the second time around if you have to take a break.
It was previously thought that the adaptations muscles make in response to strength training were completely lost over a period of several weeks because the muscle fibers were no longer being stimulated through strength training. Muscles grow in size primarily through an increase in the size of individual muscle fibers. Hormonal and neural adaptations also occur in response to training. The end result is stronger muscle that's larger in size and able to handle a heavier load. When the muscle is no longer challenged, muscle fibers decrease in size, and overall muscle size becomes smaller.
So do you completely lose all of your gains when you stop strength training? All isn't lost when you take an extended break from the gym. During the process of building new muscle, new muscle nuclei are laid down too. In one study, researchers put mice through a lower body strength training workout. The mice developed more muscle fibers and muscle nuclei as a result of training. But when they took them off of their training regimen, and they returned to a sedentary lifestyle, the additional muscle nuclei remained even though they gradually lost muscle mass over time. These extra nuclei are capable of quickly restarting protein synthesis to build more muscle once muscles are challenged again through strength training.