Dysfunctional movement is common with shoulder pain and impingement.  One dysfunction you may encounter is a downwardly rotated scapula. If upward rotation is limited, a client will display excessive shoulder flexion above 90 degrees when the humerus is in maximal internal rotation.  Typically, a person will have minimal flexion beyond 90 degrees if the scapula is moving properly.

Upward rotation of the scapula is the result of a force couple between the upper and lower trap along with the serratus anterior.  If any of these muscles are weak, rotation can be limited and overpowered by the rhomboids and levator scapulae muscles (both downward rotators).  This pattern of muscle dominance is common.

Additionally, tightness in the rhomboids, levator scapulae, pec minor or latissimus can also restrict normal mobility.  It is probably safe to assume stretching of the chest and lats would be helpful, but it is critical to encourage the proper muscle firing patterns in the traps and serratus anterior as well.

Below is a video demonstrating wall slide shrugs.  The shrug should be done at or above 90 degrees.  You can perform reps at multiple angles or move to end range and perform a series there.

Application:  The exercise is designed to encourage upward rotation in a more functional manner as opposed to traditional shrugs with the arms at the side.  While I am not opposed to traditional shrugs with little or no weight for basic elevation, this position generally tends to activate the rhomboids and levator scapulae which is not desired given their natural dominance pattern.

The wall slide shrugs should not create any pain or discomfort.  However, they may feel awkward particularly if the client has a faulty muscle activation pattern.  As muscle tightness resolves and strength improves, clients should gain more mobility and optimal shoulder function.