It is great to see people doing more overhead movements lately, whether it be with barbell, kettlebell or gymnastic movements. Many people in the US, particularly male athletes, lack full shoulder ROM. Our obsession with strength and mass, in the form of bench pressing and bicep curling, sets our basic shoulder health back.
And for whatever reason, many health professionals forget that the shoulder complex is perfectly capable of 180 degrees of flexion and abduction. Overhead movements are not inherently dangerous or bad for you; they will be painful if you have let gravity and limited activity contribute to postural issues and muscle imbalances. This only happens if you don't exercise the upper extremities through a full ROM and maintain strength and mobility throughout the shoulder girdle complex. Cartwheels anyone?
But overhead movements are not just about being strong. It is not just about having big ol' upper traps and shrugging with objects over your head. Strength is just one component of a healthy shoulder girdle complex and it involves many other muscles besides the upper traps. In my mind, the primary benefit of overhead movements is maintaining and developing normal scapulohumeral rhythm--the coordination of scapular upward/downward rotation with humeral elevation/depression.
When I say humeral elevation, I mean humeral abduction or flexion. For the humerus to elevate properly, it must have the cooperation of the scapula. This does not mean the scapula must simply elevate; something many seem to misunderstand. In fact, scapular elevation by the upper trap alone, is many times a compensation for a loss of scapulohumeral rhythm. The upper trap may grab the spotlight by being all buffed out; that doesn't mean it performs the brunt of the real work when it comes to the scapula's role in overhead movement. Big traps don't necessarily mean good shoulder health.
There's a little more to the story. The scapula also abducts, protracts and upwardly rotates as the arm elevates; it must reverse this process as the arm returns to neutral. This rotation allows for optimal contact of the humeral head in the glenoid fossa for maximal stability; it also creates room for the rotator cuff and subacromial bursa under the acromion. This coordinated movement requires work by the entire trapezius complex--middle and lower traps too, and the serratus anterior. (Note the serious serratus anterior in the picture. Today's singlets don't allow us to see full shoulder girdle musculature in the weightlifter.)
So, if you are a novice trainer or coach, before you get jiggy with it and go shouting out to the world about the "active shoulder" with overhead movements, please take the time to get a basic understanding of the biomechanics and functional anatomy of the shoulder complex. No one expects you to rehab a shoulder--that's not your job--but you should be able to have a fundamental understanding of what happens with normal overhead movement if you are going to teach it.
So get funky and hip to scapulohumeral rhythm. Scapular rotation is the key to humeral elevation.