Dead Hangs as discovered by Dr. John Kirsch are immensely effective for shoulder rehabilitation because they strengthen the acromiohumeral joint through elongation and progressive reshaping of the acromion process.
This creates more subacromial space for the tendon. Contrary to conventional belief, the dead hang relieves impingement over time. Said simply, they decompress the shoulder joint. The movement is done overhand for 30-60 second intervals, and up to 2 minutes plus as you get stronger.
If a full hang is too difficult, you can do a partial hang and offset some of your Bodyweight.
The Underhand position requires external rotation of the humerus and puts more stress on the wrist forearm elbow and biceps. It is a good Lat stretch, but it doesn’t have the same benefit as the pronated position. Overhand is how you do them.
People typically report feeling their spine stretch, especially the lumbar spine, which is normal and beneficial.
These can be done daily, if you are doing them as part of a workout, I suggest doing them at the end of the training session, although you could do a short hang at the beginning if that feels good to you. Experiment.
For more about this protocol, I recommend Dr. Kirsch’s book, the shoulder pain solution.