Watching the Step Class

So I've got a knee that is partly dead. The end of my femur bone decided to die out on me. The name the doctors use is osteochondritis dissecans. To remedy the situation and decrease pain until I have a surgery, I am wearing a leg brace. I've missed gym class for the last four months.
But gym class still continues normally for the non-impaired high school girls. That's why I'm here, sitting in a YMCA gym, watching a gym class "field trip" that I can't participate in. (Side note: If some trips aren't to a field, why are they still called field trips?)
But loud, rhythmic music buffets my ears as I watch my classmates in their step class.
My classmates step, step, step... stretch, step, step, step... stretch. I still sit here on a hard, paint chipped bench with my back against a cold, white stone wall, wishing I could join in and burn some calories but grateful that I'm not sweating.
Sometimes Bekah looks over at me and laughs, and other times she's looking at the instructor in exhaustion. My other classmates have gone from high stepping to droopy, though some are standing strong. They're all sweaty messes, though, and by the end of the lesson they all look as if they've been through a war. Step, step, step, march, march, march... stretch, stretch, stretch.