The shoulder and its muscles are a marvel of engineering by nature. In order to be able to work the shoulder muscles, it is important to have a good understanding of how the muscles work together.
The role of the trapezius muscle
The shoulder muscles are made of the trapezius and the deltoids. They usually work together so it is not possible to isolate one from the other. However, the traps muscles are situated on the upper back and serve primarily to pull back the shoulders. They snake all the way to the base of the neck and help support it. When well-developed, they look like two thick coils on the upper back separated by the spinal cord in the middle. The upper trapezius is more involved in shoulder movements as they serve to raise the shoulders vertically up. The upper trapezius is the meaty muscles you can see sloping either side of your neck just above the collar bone. When speaking of the shoulder muscles, the deltoids come to mind so the traps had to be dismissed first.
Onto the deltoid then
The name comes from the root delta, meaning a triangle. This is because the shape of the muscle which sits on top of the external part of the arms looks like an inverted triangle with the tip pointing down. The purpose of the deltoid is to raise the arm. It is made of three distinct groups – the anterior deltoid, found at the front close to the pecs, the exterior deltoids situated on the external side of the arm and the posterior deltoids, found right at the back. Due to their position and insertion into the skeleton, each of these groups performs specific actions in tandem with other muscles.
The anterior deltoid
The anterior deltoid is heavily involved when the pectoral muscles are being recruited, such as during the bench press. The anterior deltoid serves to bring the arm closer to the centre of the body and up. So a good isolation exercise for the anterior part is to stand, hold a light dumbbell in the hand with the palm facing down and raising it in front of you. Thus the anterior deltoid is not recruited during back exercises.
The posterior deltoid
This would be the role of the posterior deltoid, sitting at the back of the deltoid muscles. This muscle part is always involved to a certain extent during all back exercises as its purpose is to pull back the arm. Thus to work it in isolation, athletes usually bend their upper body over and raise their arms sideways. The posterior deltoids are being used to pull the arms back, working against gravity. It is a rather awkward movement that does not feel natural at all.
The exterior deltoid
The third and last part is the exterior deltoid whose main function is to raise the arm up from the side. It is not closely associated with either pulling or pushing muscles, that is, the pectorals or the lats. However, they play an important aesthetic role for pro bodybuilders and for those of you who want to create an illusion of grandeur: if you seek wide shoulders, the exterior deltoids are the ones to be targeted as they will ‘pop out’ from your sides, making your frame wider. Anterior and posterior deltoids, located front and back of the body, are not able to have such an effect.
The next article will discuss the shoulder barbell press which is the basic exercise for the shoulders.