Which muscle aids in the swinging motion of the arms?

The pectoralis major is a key muscle involved in movements that require swinging or pushing of the arms. It is located in the chest and plays a significant role in shoulder flexion, adduction, and internal rotation. When the arms swing, particularly in activities like running or throwing, the pectoralis major helps stabilize and control the movement of the upper arms.

This muscle's unique anatomical positioning allows it to attach to the humerus near the shoulder joint, facilitating a range of motions that are crucial for efficient arm swinging. While the trapezius contributes to shoulder movement and posture, and the biceps brachii is primarily responsible for elbow flexion, neither performs the same pivotal swinging motion as the pectoralis major. The quadriceps, on the other hand, are located in the thigh and are not involved in arm movements at all, focusing instead on the extension of the knee.

Therefore, the pectoralis major is the primary muscle that aids in the swinging motion of the arms, making it the best option in this context.