The reverse barbell shrug is an excellent way to work the trapezius muscles. This exercise is sometimes referred to as "behind-the-back shrugs." The reverse shrug minimizes the momentum that can be generated with traditional shrugs to the front of the body.
Despite popular belief, the trapezius is not part of the shoulders. It is a back muscle that allows the shoulders to move in different directions (e.g. elevating and lowering the shoulders).
Instructions for the reverse barbell shrug are listed below:
Begin with your feet shoulder width apart. Grasp the barbell behind your back using an overhand grip. Place your hands shoulder width apart. Disengage the bar from the rack. Keep your arms straight, then elevate your shoulders as high as you can. Return to the starting position and repeat the exercise as needed. Be sure to control the bar as it descends. Always maintain a straight back.
Grasp bar behind the back. Place hands approximately shoulder width apart.
Slowly lower shoulders. Repeat.