The PBN (press behind ncek) is a prime mass builder for the laterial head of the deltoids but influences the anterior portion to a lesser degree. The posterior delts are recuited as a stabling factor. Most BB'ers do not have sufficent flexability in the should girdle region (as say an Olympic lifter would) and may have trouble (injury) with this exercise at first. It would be a question of getting the shoulder area conditioned and the stiffness worked out with warm-ups (actual pressing a light, empty exercise bar behind the neck for 20 reps or so) and stretching ( one of the better shoulder stretches is just hanging from a chinning bar with differnt grip positions, as; wide, middle & close grips...think of gymnast and their shoulder flexability) in the area. When one is accustomed to the exercise than it can be very rewarding.
People tend to rush the weight on this one, so handle weight that is with-in your capacity at first. This exercise is a basic power movement, like the front press, and has been responsible for the development of muscle mass on many trainee's, so respectable heavier weight should be used as strength is advanced. Another mistake may be that the bar is lowered too far down. Might try to just touch the top of the traps and than press back up. Holding the bar too wide can give undo stress on the joints. Might use a medium grip (forearms/arms forming a 90 degree angle on the bar if possible). PBN's also have a favorable influence on increasing one's bench press. As with any overhead press (BB or DB) in will target the interlaced muscles around the ribs, triceps and back. Good Luck.
Side Bar: I and a few of my training Bud's, have done jerk presses from behind the neck with good results and respectable poundage. But not advisable to people who are new to the exercise, just an example here. The one arm side press, to my mind, is the closest a DB exercise can come to a BB PBN.
