The barbell shrug provides resistance against elevation of the scapula, therefore targeting the upper region of the trapezius. The upper trapezius is the muscular structure of the back which can also be seen from the front of an athlete, spanning from the collar bone up towards the neck.
Contrary to what some believe, there is no tangible reason to roll the shoulders forward or backward during the shrug. It is the elevation of the scapula which is recruiting the upper trapezius fibres, and the rolling of the shoulder during the lift may just lead to a higher risk of injury.
The shrug can also be performed with a set of dumbbells, or at a cable station with a low pulley. Some prefer the dumbbell variation due to greater freedom and range of motion (ROM).
If you wish to develop the upper region of the trapezius, the dumbbell shrug is the perfect exercise to do so. The exercise requires little dynamic assistance from other muscle groups, and primarily stimulates the upper region of the trapezius which is responsible for the elevation of the scapula.
There is no need to roll the shoulders forward or backward during the shrug, instead the movement should be purely linear.
It is also possible to perform the shrug with a barbell or at a cable station with a low pulley.