It's true that I have the worse possible body type for sustained g. But I don't fly aerobatics in jets and rarely see more than 4 - 6 seconds of +-g at time. I gave up on muscle a long time ago. I just don't have the frame for it. I'm built like a mountain specialist in cycling. (Well maybe in my dreams I am am built like that). For my age though I couldn't be happier. I run and occasionally bike. But here is something I learned about myself:

Exercise has no measurable effect on my body weight. This may not seem intuitive but for me it is a fact. Because of injury I have gone months without running. My morning pushups, leg lifts and situps are a religion and never get skipped. But otherwise so long as I stick to a diet low in animal protein and high in whole foods and fiber, I maintain a precise 172 day-in, day-out. Honestly I don't think I am all that unique in this regard. Look at photos and film of people prior to WW2. Most were relatively slender. And back then, formal exercise was rare and maybe even a little weird. But small farms were more common as was local produce. Food required either effort or expense and people ate less of it. And people with the means treated food as a form of health care. They took it seriously. This is still very much the case in Japan (where my wife is from) and I think that plays a big role in why obesity is less of a problem there. But the biggest killer is sugar in all its forms. The body reacts strongly to sugar, especially when the sugar comes without the expected fiber. For most people maintaining a safe body shape should be easy unless one has been raised since childhood on processed sugary foods and drinks. Kids who have, have bodies that have been completely rewired is such a way (and through no fault of their own) they will struggle all their lives no matter how well they eat. That's pretty much everything I know after having studied it casually for a year.