Muscle memory exist, you rebuild lost muscle faster!
Your muscle cells have many nuclei which you need to make the proteins which increase your muscle mass. When working out, special cells (satellite cells) enter your muscles and increase the number of nuclei so that your muscles can make more protein for growth. Even if you’ve lost your muscle mass, these extra nuclei are not lost when you stop training.
Thus you have more potential to rebuild lost muscle mass! That being said, resuming strength training as a 40-year-old after 20 years will limit you in other ways because of your age, but you will fare better than your 40-year-old friends who didn’t go to the gym in their youth!
1. Bruusgaard JC. Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining. Proc Natl Acad Sci U S A. 2010 Aug 24;107(34):15111-6.
2. Bruusgaard JC. No change in myonuclear number during muscle unloading and reloading. J Appl Physiol (1985). 2012 Jul;113(2):290-6.