For one thing; you can never bulk up as a woman like you might be picturing unless you're doing some really hardcore stuff. Meaning lifting immense amounts of wieght and constanting doing strength workouts. And not to mention you'd actually have to be taking steroids alongside all that. So it's actually toning your body while increasing energy, endurance, and not to mention metabolism. But if it's stop working than that must mean it was working at a time?
Maybe it's gotten to be too routine and your muscles have gotten used to the moves. So you might want to try something different just to shake your muscles a little bit with some new moves or just do the tae-bo tape less and replace it with some cardio or whatever you'd like.

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I went from 161-
to 149
But now I think I should
To finish the job this time
Cuz I'm still going over that pant line