Final answer:
The rhomboids muscle is considered underactive leading to arms falling forward during the overhead squat assessment. Strengthening the rhomboids and stretching the chest and shoulders can help improve this condition. Therefore, correct answer is c.
Step-by-step explanation:
The muscle considered to be underactive, leading to arms falling forward in the overhead squat assessment, would be the rhomboids.
When this muscle is weak or underactive, it can lead to a lack of scapular retraction and stabilization, causing the shoulders to round forward.
Other muscles could also play a role, such as a weak trapezius or tight pectoral muscles, but based on the choices provided, the rhomboids are the most likely culprit in this case.
Strengthening the rhomboids and other scapular retractors, along with stretching the chest and shoulders, could help correct this posture during the squat assessment.