Make an effort to look at other peoples’ bodies and note who appears more fit.
If you think of “fitness buffs” as being a special clique, then noticing other potential members of the clique and feeling like you belong to something bigger than yourself can reinforce your “fitness buff” identity. However, this technique can be very counterproductive. Women in the US and elsewhere are often socialized to compete with each other on the basis of appearance already, so noticing fitter women is already something that we do with not necessarily very positive results.
Actually, I try to keep appearance out my mind when I exercise because I’ve had issues with body dysmorphic disorder. Instead, I identify as someone who’s into, say, urban cycling. Now I notice when other people are carrying a bike helmet with them when they’re in a shop, for instance. I feel like a part of a group, and this feeling of identity encourages me to keep biking.
By the way, the idea that you can tell how fit or healthy someone is just by looking at them isn’t correct. Some thin, healthy-looking people don’t exercise, and some people who are overweight are actually quite healthy according to other measures of fitness, so I’d shy away from using appearance as a proxy for fitness.
Science classes, especially before high school level, are often taught as though science is just a collection facts about trees or dinosaurs or whatever. Anyone who hasn’t had the benefit of a good science program in their school might continue to think that science is just experiments to generate facts.