The prime mover of arm extension is the __________.

• A. deltoid
• B. latissimus dorsi
• C. quadriceps femoris
• D. pectoralis major

Answer: (B)

Verified step by step guidance

1. Identify the action described in the problem: arm extension.
2. Understand the role of a prime mover, which is the main muscle responsible for a specific movement.
3. Review the function of each muscle option provided: deltoid, latissimus dorsi, quadriceps femoris, and pectoralis major.
4. Recognize that the latissimus dorsi is primarily responsible for the extension of the arm at the shoulder joint.
5. Conclude that the latissimus dorsi is the prime mover for arm extension, as it pulls the arm backward and downward.