I read on a pretty dumb site that lying external rotations are dangerous: "While I'm at it, I would also like to kill another exercise I've seen around gyms for the past years. Ever seen a guy stand with light dumbbells in his hands, upper arms straight out to the sides and 90 degree angle in his elbows, rotating his arms from vertical to horizontal? If you ask him what he's doing, he'll proudly inform you that he is right now taking care of his rotator cuffs.
Considering what you know about two vulnerable joints in that area which gets pressed pretty tight at that angle, adding the back-and-forth motion, you can also conclude that the dude is doing a nice job of actually sawing his bicep and supraspinatus joints off."
This question is especially for Cressey and Robertson. While I consider that site full of bs (4 exercises, 3 sets each, 10 reps/set type of bs), I would appreciate an expert opinion on this.
Many thanks, Vlad