Your back is made up of an interwoven system of four muscles. They help you lift, pull, sit, and stand up straight. When toned, these muscles give you a sensationally sculpted rear view—especially come sundress season. Strengthened back muscles will help pull your shoulders back, so you stand taller and appear leaner (these 6 quick posture fixeswill also help). You’ll also play sports and perform chores with ease and be less likely to suffer from back woes. The following exercises target the muscles on your upper back, around your bra. Do two sets of 10 to 12 repetitions, with a minute of rest in between, 2 or 3 days a week. Allow a day of rest between workouts. Obviously, if you have some extra weight to lose, you’ll have to shed those pounds to see results (get a jump on weight loss—and get a fee MP3 player—with easy 8-week walking plan). But if your problem is just untoned muscles, you’ll see visible improvement in 4 to 6 weeks.  Bent-Over Row  Stand with your feet shoulder-width apart, back straight, and knees slightly bent for support. Hold a dumbbell in each hand. Keeping your back straight, bend 90 degrees from the waist and allow your arms to hang down toward the floor, palms facing your legs. Squeeze your shoulder blades together, and bend your elbows, raising the dumbbells up to either side of your torso. Hold, then slowly lower back to the starting position. MORE: 10 Things Your Breasts Say About Your Health Lateral Pull-Down with Band  Sit on the edge of a chair with your feet flat on the floor and wide apart. Wrap the ends of an exercise band around each hand, and hold it overhead. Position your left arm straight toward the ceiling (this is the anchor hand), and drop your right hand out to the side about 45 degrees. Both elbows should be slightly bent, and the band should be taut. Keeping your left arm stable, contract your back muscles and pull your right arm down until your right hand is in line with your chest. Pause, then return to the starting position. Perform a full set, then switch sides. Seated Back Fly  Sit on the edge of a chair with your feet close together and a light dumbbell in each hand. Lean forward from the waist, and let your arms hang down next to your calves, with your elbows bent slightly and your palms facing each other. Squeeze your shoulder blades together, and raise the weights to your sides in an arcing motion until your upper arms are parallel to the floor. Pause, then slowly return to the starting position. MORE: Your 5-Minute Routine For Killer, Ageless Arms Upright Row Stand with your legs about shoulder-width apart and knees slightly bent. Hold a dumbbell in each hand, arms hanging down at the outside of your thighs, palms facing back. Squeeze your shoulder blades, bend your elbows, and pull the weights up and out to the sides until your elbows reach about shoulder height. Pause, then straighten your arms and return to the starting position.