Both of these powerful muscles attach to the inside of the upper arm, which means they rotate it inward. If you perform these exercises more than you do moves that rotate your upper arms outward—such as bent-over and seated rows—your pectoralis major and lats will pull your arms inward, causing your shoulders to round forward.
This primer shows you how to train your "other" shoulder muscles. As a general rule, count the total number of sets of bench presses, shoulder presses, pullups, and lat pulldowns that you do in a week, and make sure you do an equal number of sets of exercises that work the following muscle groups.
The deltoid consists of three separate heads: the anterior head, or front deltoid; the medial head, or middle deltoid; and the posterior head, or rear deltoid. Though the shoulder press and lateral raise train the front and middle deltoids, they ignore the rear deltoid.
Exercise Rx: Try bent-over dumbbell raises and barbell bent-over rows using a wide grip. Do seated rows by pulling the rope handle to your neck instead of to your lower chest.
These four tiny muscles—the teres minor, supraspinatus, infraspinatus, and subscapularis—stabilize your upper-arm bone (the humerus) in your shoulder socket, allowing you to rotate your arm in every direction.
Exercise Rx: Bolster your rotator cuffs by working them at least twice a week with external-rotation exercises and a move called PNF.
These muscles—the trapezius, serratus anterior, pectoralis minor, rhomboid major, and rhomboid minor— llow you to move and stabilize the shoulder blades, or scapulae. According to a study, 100 percent of people with shoulder-joint problems have unstable scapulae.
Exercise Rx: Focus on rowing movements, such as the bent-over row and seated row. Initiate rows and pulldowns by squeezing your shoulder blades together.
Problem #2: Your Job
If you suffer from poor desk posture, changing your lifting habits isn't guaranteed to correct your problem. After all, the 30 minutes a day you spend exercising is only a fraction of the time you spend sitting in one position.
If your shoulders are slumped forward for long periods of time, your chest muscles become shortened. That is, since these muscles attach to your upper arms, the distance they need to extend when you slouch is less than when your shoulders are drawn back.
Over time, the chest muscles adapt to this position as their natural length, pulling your shoulders forward. As a result, many of the shoulder's stabilizers are overstretched, which makes them weaker.
Exercise Rx: Use the stretches shown in "The Perfect Posture Plan" daily. They force your chest muscles to extend, which prevents them from becoming permanently shortened.
At work, do 10 standing shoulder retractions every hour when working at a com-puter. Stand and pull your shoulders back as you squeeze your shoulder blades together. Hold each repetition for 3 seconds. And focus on keeping your head and shoulders directly above your pelvis at all times—it's an easy way to ensure that your body is in proper alignment.