Muscle tone applies a cost on others who must devote more of their time (which can be measured in dollars, by the way) toward the positional signalling game of fitness. Does this mean we should avoid conspicuous health?

Let's work this out TDT-style: if the right answer to the question "should you exercise" is "no (because that would make others jealous unless they exercise too, because then they wouldn't look as good as you)" you get a world with people who don't exercise. If it is "yes (because then you'd look better)" you get a world with people who do exercise. I'd pretty much prefer the latter world. IOW, I'm not sure that this game is purely positional (i.e. zero-sum).