"I never felt my weight get out of hand," the singer said about carrying son Max Liron, born Jan. 12, 2008. So she waited until mid-March to exercise with trainer Tee Sorge. "I do the treadmill, I box, and I do a lot of weights. I feel so much better when I work out." She also burns calories breast-feeding – and by summer, Aguilera was back in body-hugging dresses.