I was just watching a couple of "gorillas" in the gym who seemingly were admiring their torsos while performing shoulder flys. I was tempted to offer my two cents in perfecting their form -- wisely I didn't. A well balanced shoulder routine should include exercises that strengthen the "back" side of the shoulders. These include the rotator muscles of the shoulder, rhomboids and mid-trapezious muscles; keeping your back more erect -- a non-slouching position with your shoulders back.
This posture is the optimal position for almost all sports, except curling and a few others. If you are participating in triathlons, you don't want to be internally rotated with tight abs during the swim, bike or run. Even though your elbows are drawn inwards in the aero position on the bike, you'll end up losing power on the downward part of your pedal stroke if you aren't long through your torso and midsection -- again strength through the upper and mid-back is needed to hold this position. When I teach people to sit properly on their bike, I have them put their hands on the stem and then draw a line from their hands to their naval, folding at this point.
One simple way to work the mid-traps is to use a stretch-cord row from a standing position. Loop the stretch cord around a bar so you are holding a handle in each hand. With the handle height at about your lower rib cage, start by gently retracting your shoulder blades so your shoulders are slightly drawn back. When the stretch cord goes forward, make sure you aren't internally rotating your shoulders. You don't want to have the rounded shoulder position at all throughout the whole exercise.
As your arms go forward, stop them with about a 160 degree bend in the elbow. They aren't fully extended. Keep the light tension between your shoulder blades. As you row toward your body and increase the tension on the cord, your arm flexion at your elbows is about 90 degrees with your elbows close to your side. You can "pulse" it there as if you're sawing a log, six to ten times. Concentrate on squeezing the muscles between your shoulder blades not using your posterior deltoids.
You can also an another element by bending over at your naval -- similar to your position on the bike -- while keeping your back straight. Do the rows with your thumbs up to start, rotating to palms up when you finish. You'll really feel this in your mid-back. For each exercise, complete 10-15 reps.
These simple exercises are a perfect addition for all athletes -- endurance and power. Are these the only two? Absolutely not. However, they will give you a start to enhancing your posture and mid-back strength.