Two out of every three people will experience a shoulder injury or problem at some point in their lives.
One reason: When it comes to training, the anterior, or front, deltoid muscle gets almost all the attention, while the medial and posterior deltoids get the cold shoulder.
For a study sponsored by the American Council on Exercise, scientists from the University of Wisconsin La Crosse evaluated popular shoulder exercises to see which were most effective.
Popular Deltoid Strength-Training Exercises
While no single exercise can work all three parts, start building a shoulder workout with two that target most of the muscles. Build up to three sets of eight to 15 reps each. At first, you may only be able to lift very light dumbbells, but with consistency, you'll develop strength over time. When you can complete three full sets, it's time to increase your weight.
For the seated rear lateral raise, sit on the edge of a bench, feet flat on the floor, a dumbbell next to each foot. Bend over to bring your torso as close as you can to your thighs. Hold a weight in each hand with elbows bent slightly so that each weight is against the outside of each calf. Slowly lift your arms out to the sides and up to shoulder height; your back should stay straight and not move. With control, slowly bring the weights back to start. Repeat up to 15 times.
For the dumbbell shoulder press, stand with feet hip-width apart, knees slightly bent. With a dumbbell in each hand, raise your arms out to the sides until level with your shoulders. Bend your elbows so that your forearms make 90-degree angles with your upper arms, then rotate wrists so that palms are facing forward. This is the start position. Slowly straighten your arms up toward the ceiling. Then with control, lower them to start. Repeat up to 15 times.
Always start a shoulder workout with exercises that target the posterior deltoids because they're the weakest of the group. As a reminder, strength train no more than three times a week, allowing 48 hours between sessions, and always after warming up the body with light cardio activity.
The American Council on Exercise has an extensive library of deltoid exercises and how to do them safely.