Having been in and out of shape a couple of times in life, a few times in excellent shape (at least with regards to specific sports and skills) and having bounced back from a 4-5 year slump about a year and a half ago, it does seem that the body (both muscles and conditioning) have a certain degree of “memory” and adapt accordingly even after a few years of not training.
I’m sure there is a factor of learning your body and how its responds to different types of training and conditioning through various stages in life as well, but the body does seem to respond faster to training if you have been in shape before as opposed to starting from scratch.
A person who is exposed to conditioning at a young age could literally be programming their DNA, or re programming their DNA, and be more physically adaptive for the rest of their life. This idea would seem to be supported by the conclusions of this study. I suspect the same could be applied to diet.
Interestingly, many of the methylation changes were on portions of the genome known as enhancers that can amplify the expression of proteins by genes. And gene expression was noticeably increased or changed in thousands of the muscle-cell genes that the researchers studied.
Most of the genes in question are known to play a role in energy metabolism, insulin response and inflammation within muscles. In other words, they affect how healthy and fit our muscles — and bodies — become.