I did some research on this a few years back, and, from what I found, it matters a little.

If someone is a body builder and gets MG, they can still become very weak and go into a crisis. So a "starting" point of muscle strength before MG might help fend off atrophy in the long run, but the MG process is still in play.

There were some studies (PubMed) that showed that staying as strong as you can does help, but the studies really weren't that great.

Once you have MG, it's harder to regain muscles, but it's not impossible.

As to the issue of more muscle receptors, I honestly don't know if a more developed muscle has more receptors. I'd have to do more research and, frankly, I'm beat lately. You'd have to look up if we're born with a certain set of receptors, if you want to do the research yourself.

Can a person "grow" muscle receptors past a certain age? I don't know. We are still building brain cells and bone density into our teens and twenties.

I don't have an answer, but I hope that sends you off into a good direction.

Annie