Photo by Bruce Klemens.
The shoulder is a marvelous thing. Designed for maximal mobility for our bipedal, upright selves, it lacks the bony stability of the hip. Thus, it relies on active (muscle, tendon) and passive (ligament, joint capsule) structures around the joint to provide maximal stability with the overhead lifts; there is no ball/socket mechanism to rely upon. For the upper body to receive heavy overhead loads, we need to optimize the shoulder position to support not only the weight, but also put the wrist and the elbow in a strong, safe position. This is especially important in the snatch, with the wide grip.
At a weightlifting meet, you'll hear coaches yell "push" or "reach" to their athletes. The athlete must aggressively resist the downward forces of gravity and barbell to successfully receive the bar and complete the lift. Many people confuse this aggressive "push" with a shrug of the upper trap. Yes, the upper traps are strong, but we do not want to elevate the shoulder girdle and decrease approximation of the scapula on the rib cage; nor do even want to think we can hold that weight up with upper body muscular strength. We receive the bar at arms length, lock the wrist and elbow in a fully extended position, and maximize contact of the scapula with the thorax via serious isometric contraction of scapular stabilizers. The human body supports the overhead load with the greatest area of bony stability possible, and transfers that force over the entire musculoskeletal system.
The "active shoulder" musculature used by competitive weightlifters is the serratus anterior, the rhomboids and the middle traps. These aren't big, sexy muscles, like the upper traps are, so it might be more difficult for some of you to see and appreciate what is happening. But these little guys are the muscles you want to engage when receiving a snatch or jerk. These muscles also help the scapula upwardly rotate, rather than elevate, to give the rotator cuff room and seat the humerus in the glenoid cavity of the scapula.
Think of it as supporting the weight from the bottom of the scapula, not the top. Resisting the downward push of the weight with an isometric hold, not a concentric shrug up. Remember, we are stronger eccentrically and isometrically. The only way a human being can support 2-3x bodyweight overhead is to create a platform of maximal musculoskeletal stability, and that means keeping as much of the scapula as possible on the rib cage.
More on the shoulder and proper overhead positioning later this week.