
Levator Scapulae is situated at the back of your neck, it originates at the first four cervical vertebrae and attaches on to the medial angle of the scapula. At the top it lies under the sternocleidomastoid but most of it is deep to the large trapezius muscle.
As its name suggests it's primary action is to elevate the scapula. It's involved, along with the upper traps, in lateral flexion (unilaterally) and extension (bilaterally) of the neck. It also acts to stabilise the scapula.
If levator scapulae is chronically tense it won't lengthen to allow the scapula to rotate. This restricts the movement of the shoulder and can cause problems elsewhere. The shoulder introduction explains the role of the scapula in shoulder movement and what can happen when it goes wrong.
When you're tense and you're shoulders lift up it's levator scapulae that is shortening. Notice how when you're on the phone or in the car your shoulders will creep up. It's as if the stress is going directly into levator scapulae. A lot of the relaxation exercises are aimed at releasing this tension.
Holding your instrument on a strap over your shoulder will effect levator scapulae so, as with trapezius, try to keep your chest open to take allow your skeleton to take the load