I imagine person B as someone who doesn't do formal exercise at all. If their capacity for exercise goes down, they might think vaguely that they're a little sick or getting older, but they've never been concerned with the details of how much they can do, and it's going to a good-sized change for them to notice it.
However, I'm not sure this pattern extends to reading-- some smart people who read easily seem to have the metaphorical proof-reading/copy-editing gene.
Well then actual fitness level is basically irrelevant, and the ability for someone to notice the effects of the environment change is based mostly upon the factor of whether or not they do any excercise.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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