Legs-Chest-Back These are the three largest main muscle groups of the body.Your metabolism will be affected most if these muscles are emphasized during your workouts! I know women are afraid of lifting with their legs out of fear of getting too bulky,but we don't have the levels of testosterone to build bulky muscles! So make sure you use these potential "fat furnaces". Build up your chest for a natural breast lift.Strong active chest muscles burn fat! Last but not least, your back, weak back muscles cause most of our pain.Strong back muscles burn fat.