The 5 Main Muscles of Movement.
Anatomy in detail:
The left and right trapezius muscles form the most superficial muscle layer of the upper back and neck.
The trapezii (plural) form a kite-shaped sheet of muscle from mid-back to the back of the head, shoulder to shoulder.
Wikipedia: Trapezius: from Late Latin trapezium, from Greek τραπέζιον (trapézion), literally "a little table", a diminutive of τράπεζα (trápeza), "a table", itself from τετράς (tetrás), "four" + πέζα (péza), "a foot; end, border, edge"
The trapezii are large, thin muscles that meet midline.
They are sculpted down the sides of the neck and extend out to each shoulder, attaching to both the scapula (shoulder blade) and clavicle (collar bone) of each arm.
The whole of each muscle should be free to fully extend, without pain or tension, supporting the head and arms through a full range of natural movement.
The left and right trapezius muscles attach to the cervical and thoracic vertebrae (bones of the spine) via the nuchal & supraspinous ligaments making them responsible for the alignment of the upper body.
Sensory information provided by the trapezii gives us information about the relative positioning of thoracic and cervical spine. This knowledge allows us to feel how to move to improve posture.
Current descriptions split each trapezius into 3 functional sections - the upper, middle and lower trapezius, based on the direction of the muscle fibres.
a.k.a. superior (i.e. higher than the other sections) trapezius.
a.k.a. descending (i.e. the muscle fibres descend) trapezius.
The upper trapezius attaches to:
a.k.a. transverse (i.e. the muscle fibres run approx. horizontally) trapezius.
The middle trapezius attaches to:
a.k.a. inferior (i.e. lower than the other sections) trapezius.
a.k.a. ascending (i.e. the muscle fibres ascend) trapezius.
The lower trapezius attaches to:
Movement of the upper body should begin from the lower trapezius.
With Base-Line support in place, think of activating both your lower trapezii starting from midback, extending upwards and outwards towards your shoulder blades.
Between the 6th cervical and 3rd thoracic vertebrae (the base of the nuchal ligament and start of the supraspinous ligament) the trapezius muscles are connected to the midline by a broad semi-elliptical aponeurosis (thin sheet of strong connective tissue), forming a tendinous ellipse between the shoulder blades.
The trapezii should be free of restrictions, guiding the head and arms through a full range of natural movement when connected to Base-Line support (pelvic floor and rectus abdominis).
The trapezius muscles are responsible for the alignment of the upper body, capable of positioning the nuchal and supraspinous ligaments to align with the linea alba and create the median plane.