The resistance band side lateral raise is a great exercise for strengthening the shoulder muscles and rear deltoids. This is a great rehabilitation for the middle of your shoulders with great emphasis on toning and strengthening your upper arms throughout the exercise. I would normally complete this exercise with a light resistance band to start with, as you will be extending and stretching the band extra for this movement. 

Method 

Starting with the resistance band underneath both feet, you are going to hold each handle of the resistance band loosely at your sides, palms facing in.

Then with an exhale bring both arms up until your body is in the shape of a T. Hold this pose then release back down into the starting position.