Does this "fit" here mean "slender"? The translation goes like that, but I have known it as "healthy".
ex)Physically fit people often without sensing it. Take two men who are the same age and height ─
everything is the same except that one is fat and the other one is fit. When these men go out shopping, the fit one will probably move more quickly and farther and use slightly more calories than the fatter one. And so it goes with other activities. In contrast, the fatter man has adapted to a low
activity rate, so he doesn’t move as much during any given activity as the fit one.