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The muscle primarily responsible for shoulder girdle elevation during shrugs is the upper trapezius. This muscle plays a significant role in elevating the scapula, which is the action observed when performing shoulder shrugs. The upper trapezius fibers contract to lift the shoulder girdle upward, which is crucial for the movement involved in this exercise.

In addition to elevation, the upper trapezius also aids in the upward rotation of the scapula, which is essential for proper shoulder mechanics and functionality during overhead movements. Its strategic positioning on the upper back and neck allows it to effectively perform these functions.

The other muscles listed have different primary functions. While the latissimus dorsi is involved in shoulder extension and adduction, the rhomboids mainly retract and elevate the scapula without providing the primary lifting force during a shrug. The deltoids primarily function to move the shoulder itself rather than specifically elevating the scapula. Therefore, the unique role of the upper trapezius makes it the correct muscle responsible for shoulder girdle elevation in this context.