For everyone that put behind the back shrugs? Wtf? Seriously. How do you even think that a movement that is not natural and trying to work a muscle not going with its grain of movement is effective.
The traps don't just pull the shoulders up, they also hold the shoulder blades in places and can squeeze them together.
IMO, shrugs are the smith machine of trap exercises. Drop them for more efficient ones. Farmers, frame carries are even better. Snatch grip deeds especially from blocks. High pulls. Muscle hang power snatch. Face pulls. All far superior to shrug.