The shoulder involves more than one joint.  It is a complex structure with two important, but somewhat contradictory roles.  It must be very flexible to allow the hand and arm the big range of motion they require.  It must provide a strong and stable fixed point for tasks like lifting heavy objects or pushing against resistance, for example.  There are many bones and muscles involved in the shoulder and when the biomechanics are wrong or repetitive movement is present, injury may occur.

6 + 2 is a series of exercises to strengthen or rehab the shoulder complex.