What are the features of the shoulder?

 
The most mobile joints in the human body
Basic structure to move the hand
Essential joint for ADL (activities of daily lving) and sports
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Shoulder joint plays an important role for your quality of life.
 
The structure of the shoulder gives us a wide range of movement at the expense of instability. Therefore, it may provoke problems even by moving hands in different directions.
Paradoxically, the shoulder joint needs stability and flexibility at a time.
 
Shoulder joint is like a golf tee and a ball. You might feel stable when a ball stays still on a golf tee. That is when your shoulder joint is put in place for the next movement. However, once a ball becomes unstable, that is when you feel uncomfortable on the shoulder.