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Extensor Stretch

Execution
     
Squat while facing a doorway, with the right shoulder lined up with the left side of the doorjamb.
Stick the right arm through the doorway. Grab the inside of the doorjamb at shoulder level with the right hand.
While keeping the right arm straight and the feet firmly planted, lower the buttocks toward the floor.
Repeat these steps for the opposite arm.
Muscles Stretched
     
Most-stretched muscles: Right posterior deltoid, right middle trapezius, right triceps brachii, right teres major, right rhomboids, right infraspinatus
Less-stretched muscles: Right latissimus dorsi, right teres minor, right supraspinatus, right serratus anterior
Stretch Notes
Although poor posture has a negative effect on both sides of the body and results in overall tightness, most people use one arm more than the other, so the muscles on one side can become tighter from disuse. This is especially possible when doing any overhead work such as painting, window washing, or overhead presses. These activities may become harder and more painful. Thus sometimes you may need to stretch one side more than the other. Since this stretch mimics single-arm overhead work, it is better suited for problems arising from one side being tighter than the other. Also, by stretching one side singularly with gravity assistance, this stretch allows for a greater amount of stretch than any of the other stretches that work similar muscles. Moreover, this stretch relieves many of the aches and pains felt between the shoulder blades.
A lower squat yields a greater stretch, but it increases the pressure and strain on the knee joints. Therefore, be careful not to squat so low that you feel pain in the legs or knees. To reduce strain on the knees, change the point where you grab the doorjamb. Changing the position of the grasp, however, influences the amount of stretch placed on the various muscles (see variation). Regardless of where you grasp, keep the back straight or arched. Do not bend forward at the waist. To get an even greater stretch, inwardly rotate the trunk.
VARIATION
Overhead Shoulder Adductor and Extensor Stretch

Grasping the inside of the doorjamb above head level reduces the stretch on the middle trapezius and allows a greater stretch of the posterior deltoid, latissimus dorsi, triceps brachii, teres major, and infraspinatus. Begin the stretch by squatting in front of a doorway, with the right shoulder in line with the left side of the doorjamb. Stick the right arm through the doorway, and, with the right hand, grab the inside of the doorjamb several inches above your head. Increase the stretch by lowering the buttocks toward the floor. Repeat again for the opposite side.

Assisted Shoulder Abductor Stretch

Safety tip Pull the elbow back gently.
Execution
     
Stand upright with feet shoulder-width apart, with the toes pointing straight forward.
Bring your left arm behind your back, with the elbow bent at 90 degrees.
Have a partner stand behind you facing your back and grasp the left elbow.
The partner gently pulls the elbow back and up toward the head, taking care not to pull suddenly or with great force.
Repeat these steps for the opposite arm.
Muscles Stretched
     
Most-stretched muscles: Left supraspinatus, left infraspinatus
Less-stretched muscles: Left anterior deltoid, left pectoralis major, left teres minor, left coracobrachialis
Stretch Notes
The supraspinatus and infraspinatus muscles can become tight when a person does either repeated forward pushing actions, as when using a walk-behind lawn mower, or downward pulling actions, such as raising something off the ground using a block-and-tackle pulley system. The supraspinatus especially is always working during overhead movements and so can be easily strained when it fatigues. This stretch can also help relieve the pain associated with shoulder impingement, shoulder bursitis, rotator cuff tendinitis, and frozen shoulder.
If you have ever had someone twist your arm behind your