When performing a shoulder shrug, which muscle primarily assists in elevating the scapula?

The upper trapezius is primarily responsible for elevating the scapula during a shoulder shrug. This muscle originates from the base of the skull and the cervical spine and inserts on the lateral aspect of the clavicle and the acromion of the scapula. When the upper trapezius contracts, it pulls the shoulder girdle upward, resulting in the elevation of the scapula.

The levator scapulae also assists in scapular elevation, but it is not the principal muscle engaged during a shoulder shrug. It primarily comes into play with more targeted movements of the scapula, such as when rotating the neck or raising the shoulder blade.

The rhomboids are mainly involved in retracting the scapula, drawing it towards the spine, and stabilizing it during various upper limb movements rather than elevating it.

The middle trapezius primarily functions to retract the scapula, thus it does not play a significant role in elevation during a shoulder shrug.

In summary, the upper trapezius is the most active muscle for scapular elevation in this particular movement, making it the correct choice.