The supraspinatus is one of the four rotator cuff muscles. It is is located on the top part of the shoulder blade, starting at its inside edge and running to the head of the upper arm bone. Supraspinatus tendonitis is an inflammation of the tendon that attaches the muscle to the bone.

Initial Treatment:

First try to reduce inflammation and pain. Do range of motion exercises only to prevent the muscles from becoming tighter than they already are. Simply move your arm forward and back, out to the side and overhead, and in circles. Be gentle and do not push beyond your pain boundaries. After the initial inflammation subsides, you can move on to a more complete exercise program.

Supraspinatus Tendonitis Exercise Program:

Massage & Bodywork magazine recommends the following exercise program for supraspinatus tendonitis. You must do the exercises every day, seven days a week, for six to eight weeks for the program to be effective.

Warm up: Stand with your arm 5-8cm in front of your body and make a big, slow circle in front of you for three or four minutes. Make the circle only as large as you can without pain.

Stretch: Stand with your back to a doorknob. Grip the doorknob with your arm behind you and lunge slowly forward with one foot in front of the other, keeping the gripping hand in line with your spine as you stretch. Hold the stretch for 30 seconds. Rest for 30 seconds. Repeat five times. Go to the point of feeling only a mild pulling sensation in the shoulder, not pain.

Strengthening Exercise: 

You will do this exercise for three sets of 10 repetitions. Only the third set should cause some tiredness or stress in your shoulder. If you feel stress before the third set, you are using too much weight. Stop, and the next day use less weight. If you feel no tiredness or stress in the third set, you are not using enough weight. The next day, add a little more weight.

When you begin this exercise program, if any weight is too much, use no weight. Add weight at 250g or 500g increments. Most people need to start with 0.5kg-1kg and build up to around 2.5kg over the next six to eight weeks.

The exercise: Lie on your side with the injured arm toward the ceiling. Holding the appropriate weight, lift the arm slowly toward the ceiling through about 20 to 30 degrees, then bring it back down to your side without resting it on your hip.

If even no weight causes discomfort, bend your arm at the elbow to about 90 degrees and lift it from that position. Use the same weight for a week or until the exercise feels easy, whichever is longer. Then add weight (usually a 500g increment).

Next, repeat the stretch five times. Then apply ice or heat to the affected area for five minutes.

Please note:  This article is not a substitute for a professional consultation.

(Source: http://www.ehow.com/way_6174300_exercises-supraspinatus-tendonitis.html)
Measurements converted to metric.