I was always under the impression that the healthy BF% range was 18-25% But I have a friend who goes to Curves gym and she says that that range is what they term 'athletic' and that 'healthy' is a higher range...what's the truth?

Right now I'm WAY out of any variation of the 'healthy range' (although I've dropped about 8% BF so far) I just want to know what range I should be setting my sights for.

Also, does your lean muscle mass change as you lose weight? I had a BF test done a year ago, and it said I have 137lbs of lean muscle mass, will that stay true or will it go down as I lose weight?