Muscle memory is the ability of the muscles to “remember” previous strength and recall it more efficiently in the future. Said in other words, muscle memory describes as the ability to regain muscle mass in previously trained muscles.
This means that once you’ve gained muscle mass through strength training and if you lose it after taking time off from training, you can regain the muscle mass faster than the amount of time that it took to put it on in the first place. This ability can benefit athletes in several ways. Muscle memory gives them the opportunity to rest longer periods from training. When an athlete works out again, they will be able to return to their desirable state.
Athletes who once were great shape will have quicker recovery after injury. Athletes who have developed muscle memory are able to regain their pre-injury strength and skill level more quickly.
This is how it all works
When you train a lot the number of muscle fiber will increase as muscle mass increases. You will never loose these muscle fibers. When you start working out after a break your muscles already has the increased levels of muscle fiber from when you last worked out. Therefore, you will become as strong as you once were very quick.
It’s important to note that muscle memory does not happen overnight, it takes time and consistent training for the brain to form those connections and for the muscles to remember the movement.
https://journals.physiology.org/doi/full/10.1152/japplphysiol.00761.2019
https://blog.nasm.org/muscle-memory