My last post on this........they are your elbows, do as you please. In the following you tube video, the guy doing rear dealts is isolating them as much as humanly possible. ANY arm extension with a dumbell in your hand with your elbow straightened, DOES impact the elbow joint, it's a simple matter of physics and gravity acting on the weight, period. You say you have no stress, fine........but do that movement for 10-15-20 years, and then tell me about your elbow. How many pro's will tell you that behind the neck military presses completely wrecked their rotator cuffs? I can think of 7 off the top of my head. But while they were doing them for years on end they had no issues. Ask Dave Palumbo who can't even raise his arms over his head at age 41. Do you see that forearm support in my avatar? You'll be wearing two of them by then.
In closing in my FINAL post on the subject........I would like to ask the queston, when did SWINGING any weight, become a good idea? In that movement you are only hitting the delt at the upper 3rd of the movement. The rest is a complete waste of time, energy, and common sense.
To each their own........go forth and tear tendons!
Proper rear dealt technique:
YouTube - Rear Delt L Raises
More good form:
YouTube - 70 lb seated bent over rear delt raises for 13 reps at 19 (bdw 170)
More good info:
YouTube - IFBB Pro Chris Cook teaches rear deltoid technique from GMV