>>excessive use of performance-enhancing drugs is not the best bet for longevity

I'd make an exception for creatine monohydrate. there's good evidence that taking some can help stave off sarcopenia - and I'm starting to see studies showing that it helps maintain cognitive function.

We can make creatine on our own (de novo synthesis) from methionine, glycine, and arginine, but the pathway requires methyl donation. Easiest solution is to just ingest some creatine (no need for the massive quantities the bodybuilders take — so agreed on the ‘no need for excessive’)

Also: our ability to recycle amino acids (AKA 'protein') drops off as we get older. Younger people don't need all that much for muscle maintenance (and kids can grow muscles on surprisingly little) But as we get older, we need to up the protein input.

BTW, there's a somewhat recent interview on Peter Attia's podcast that goes into detail on amino acid recycling and protein needs. Worth a listen.

All that said, I have to wonder as to the effects of sedentary behavior not just on mitochondria, but on the production of Cytochrome C Oxidase. The mitochondrial DNA seems to be involved in production, and as cellular mitochondrial population drops off, so does CCO - and there seems to be a connection between not having enough of that and dementia - look at Francisco Gonzalez-Lima's work. I've no evidence on this, but it seems there might be a 'point of no return' with CCO, below which there are electron transfer chain issues for all the mitochondria in the cell. Gonzalez-Lima has demonstrated that this is somewhat reversable with methylene blue (electron donation) - and I have to wonder if that would help muscle tissues as well...

Just thinking aloud here...