Who says the only way to lose weight is by running miles on the treadmill every day or becoming a Spin class devotee? Sure, cardio is helpful, but along with a healthy diet, you can also shed pounds by hitting the weights--hard. Take it from Jamie Corso, a trainer at David Barton Gym in New York City who also competes in national fitness competitions. She designed four weight-lifting workouts, all under an hour, to help you drop a dress size in four weeks.