Final answer:
The underactive muscle group during scapular elevation in a Pushing assessment is the lower trapezius.
Step-by-step explanation:
If there's scapular elevation during a Pushing assessment, the muscle group that is likely underactive is the lower trapezius. The lower trapezius is responsible for depressing and retracting the scapulae. When it is underactive, the upper trapezius and levator scapulae muscles may compensate by elevating the scapulae instead of properly stabilizing them.