My eldest son started working out at the gym this year.
It’s really great!
Something I tell him all the time is:
…once you gain good muscle, you will keep it the rest of his life
What I mean is, if he stops for some period of time then later, with modest retraining, he’ll be able to get back to the same tone/size. Or something like that.
I tell him that once you gain the increased number of muscle cells, you keep them. They may shrink if you stop training, but they are there waiting to grow as soon as you start up the exercise regime again.
It seems this is called “muscle memory”, not to be confused with the effect of nerve cells:
Muscle memory (strength training), Wikipedia
I know this both from reading and from experience. I can stop running for years, start up again and do easy 5km and 10km runs many times per week. I stop lifting, come back to it and my arms are “big” (for me) within a week or two. Experiencing it makes it more real to me and the basis for pushing the rationale on him.
Here’s a nice summary via gpt5.2:
When people gain muscle through resistance training, individual muscle fibers grow and, importantly, acquire additional nuclei from satellite cells to support the larger fiber size; if training stops, the fibers shrink (atrophy) but most of these extra nuclei are retained for a long time, possibly years. Because the nuclei remain, the muscle can ramp protein synthesis back up much faster when training resumes, allowing previously trained muscle to regain its former size and strength more quickly than muscle being trained for the first time. This phenomenon—often called muscle “memory”—is a cellular effect supported by experimental and human evidence, and it explains why regaining lost muscle typically requires less time and effort than building it initially.
I was thinking about this and thinking about how easily I gain fat.
I will eat some bread one day and gain a bunch of kg that take a week to lose. I eat badly for a few days and you can visibly see the fat around my midsection growing.
It sucks.
I was thinking that because I used to be heavier (fatter!) by about 30kg (at one short period of my life), I have more fat cells and they don’t die. Like exercise and increased muscle cells, they are sitting there, waiting for spiking insulin to steal calories and grow (store energy).
And the body defends against losing them, meaning, when they die, they are replaced.
This is a biological rational for my carb/sugar-intolerant current state of being.
It seems gpt agrees:
People who have previously been overweight or obese usually carry a lasting biological legacy in their fat tissue: during weight gain, fat mass increases not only because existing fat cells grow larger, but also because new fat cells are created, and when weight is later lost those cells typically shrink rather than die. As a result, the body retains a higher number of fat cells, which remain metabolically active and hormonally sensitive—especially to insulin, the signal that promotes fat storage. When insulin levels are frequently elevated, these shrunken fat cells are primed to refill, making fat regain easier than it was the first time weight was gained. This does not mean regain is inevitable, but it does mean the body tends to defend its previous higher weight, increasing hunger and lowering energy expenditure when calories rise. Consequently, people who were previously heavy often need to maintain long-term dietary vigilance and metabolic support (such as sufficient protein and resistance training) to keep fat cells small, because the underlying storage capacity remains even after successful weight loss.
Bingo!
It seems that there is no “muscle memory” term for this effect of fat cells.
Maybe we can call it “set point theory” or “metabolic adaptation” but these are weak and not on point.
Perhaps “adipose tissue memory” or better yet: “fat memory”!!??
Nevertheless, we lose fat and muscle as we age. Especially muscle, e.g. sarcopenia. And visceral fat increases.
But that whole different thing.
Anyway. Keep working out and eating clean! Forever!