The main muscles that make up the middle back are the rhomboids, lower trapezius and the latissimus dorsi. Middle back strength and correct posture are important to many physical activities, and participation in exercises that develop and condition these large muscles can help prevent injury. The most efficient way to work the middle back muscles is by doing compound exercises, or those that work several muscles, or muscle groups, at the same time.
Bent-over rows are a general compound back-strengthening exercise that target several middle back muscles, such as the middle and lower trapezius, rhomboids and latissimus dorsi. To perform this exercise, place one knee and one hand on a bench. Position the foot of your opposite, supporting leg slightly back and to the side. Grasp a mid- to heavy-weighted dumbbell from the floor. "Pull" the dumbbell up to the side until it barely touches your ribs or just past the point where your upper arm is parallel with the floor. Return to the starting position by slowly extending the arm until you feel a stretch in your shoulder blade. Avoid "heaving" the weight up by using momentum. Complete desired repetitions and repeat on the other side.
The latissimus dorsi, located on either side of the middle outer back, is the largest back muscle. The wide grip pull-up, another compound exercise, is a rigorous strength training exercise that targets these muscles using your own body weight, according to the MyFit.ca website. To make this exercise easier, use an assisted pull-up machine--which allows you to pull up a portion of your total body weight. Hold the pull-up bar with palms facing toward the bar, using a grip wider than shoulder-width. Hang from the bar freely if you are using your total body weight or place them on the assistance platform or lever if performing assisted pull-ups. Pull you body up until your neck meets the bar. Slowly reverse the movement, lowering your body back down.
Cable Seated Rows
Cable straight-back seated rows enable you to work the entire middle back in one fluid movement. As a general back exercise, this movement targets the middle and lower trapezius muscle fibers, the latissimus dorsi, rhomboids, posterior deltoids and other middle and upper back muscles. Using a wide-grip lat bar to perform the exercise shifts the focus of the work onto the middle back. The narrow grip handle attachment focuses work more on the lats. Sit slightly forward on a vertical platform, grasping the narrow-grip cable attachment in your palms. Keep your lower back upright and slide your hips backward, bending your knees. Slowly and firmly pull the cable attachment toward your waist, pinching your shoulder blades at the top of the movement. Arch your back slightly to help you lift your chest and retract your shoulders. Return to the starting movement -- arms extended, back straight and shoulders stretched forward.