The deltoid muscle is primarily responsible for which action?

• A. Raise arms in all directions at the shoulders
• B. Bend the elbow
• C. Extend the knee
• D. Rotate the trunk

Answer: (A)

The movement most associated with the deltoid is lifting the arm at the shoulder. The deltoid is the main shoulder muscle for abduction, especially its middle fibers, which pull the arm out to the side. The front part can help lift the arm forward and rotate it inward, while the back part can help lift it backward and rotate it outward. That’s why this muscle is best described as responsible for raising the arm at the shoulder. The other actions involve different joints and muscles: bending the elbow uses elbow flexors like the biceps, extending the knee uses the quadriceps, and rotating the trunk involves core muscles. So, raising the arm at the shoulder is the primary function of the deltoid.