Muscle Of The Month – Trapezius
The Trapezius Muscle
The trapezius muscle as a whole, is a huge muscle with three sections – the upper, middle and lower portions. It is the most superficial muscle of the upper back, neck and shoulders and it goes from the base of your skull, along to the tip of your shoulder and all the way down the middle of your back, see image below.
The three parts of the trapezius muscle are usually described as having differing functions on the action of the scapula (the shoulder blade).
In reality, this muscle acts with other muscles in synchrony to achieve optimum movement of the shoulder and it is when there is imbalance between the movement of the trapezius and the other muscles that problems arise. For example, to move the arm away from the body above 40 degrees without the upper arm jamming under the shoulder blade, the upper trapezius needs to act with the serratus anterior to rotate the scapular.
Serratus Anterior starts to pull the scapular laterally around the chest wall then the lower trapezius start to resist this, so this combined action starts to create the upward rotation movement on the scapular, which is then assisted by the upper trapezius muscle fibres once upward rotation has already started and the arm is roughly in 30°- 45° of elevation.
Serratus Anterior Muscle
The lower trapezius is a scapular stabilizer, meaning it holds the shoulder blade down as we do overhead arm movements. What happens if your upper trapezius is over tight, which we see when you sit in front of a computer for long periods with your head forwards, is that muscles like the serratus anterior and the lower trapezius become weaker and then they are not able to offer any effective counter against the tight, shrugging upper trapezius and levator scapula muscles and pain in the neck can result.
The majority of the upper trapezius muscle fibres attach on to the upper part of the clavicle (collar bone) and due to the orientation of the clavicle when these fibres contract they rotate the clavicle.. This rotation of clavicle rotation also helps compress the sternoclavicular joint, and this compression allows a transfer of the load from the arm and shoulder away from the neck and its facet joints and down through into the collar bone, into our sternum and rib cage, which takes the pressure off our neck joints.