Derived from the term Betty, which refers to a hot chick. Sweaty Bettys are attractive, stylish, self confident and extremely fit. They are often seen around town either coming from or going to some sort of work out. And, they always look good doing it. A Sweaty Betty is typically a nice-looking, mature woman who is fit and therefore quite the Betty.
I'd like to train with that Sweaty Betty.
Running is more fun with a Sweaty Betty.