Shrugs with Barbell
On the upper back is a muscle called the trapezius. The muscle looks a bit like a flying kite. It attaches to the top of the skull and extends to the shoulders. Then the muscle continues down along the spine between the shoulder blades a reasonable distance down the back. The upper part of this muscle holds the skull in place, which you can see in wrestlers and boxers who often have a well-developed Trapezius, but it also helps the body carry really heavy things or do deadlifts or Farmers walk. In the upper part of the muscle, the muscle fibers go obliquely upwards. You train this part by holding heavy things in your hands or pulling your shoulders up towards your ears when you have heavy items in your hands. This is exactly what you do in a Shrug, whether you are lifting dumbbells or a writing bar.