All I want to so is tone up my stomach and arms a little any maybe my legs ( even though they're really skinny and I don't want to make them smaller :/ ). I'm 16 a girl 5'3 and 106 lbs. I have very little body fat and am thin (i don't want to lose weight). I'm joining the gym and want to know what machines to use to get my desired results and how long it might take.