'FIT'NESS

I know a person that teaches a class at the 2 different gym locations. To look at her one would not conclude that she was anywhere near fit enough to actually teach a class. She's what one would not only classify as a 'big boned' individual but she also has a wide middle with stomach rolls.

But that got me thinking about what is fit? Does fit mean a muscular, athletic build? Or does fitness come in all shapes and sizes??