The sternocleidomastoid action of flexion of the neck is an example of _______________ contraction.

The action of flexion of the neck performed by the sternocleidomastoid muscle is indeed an example of a concentric contraction. This type of contraction occurs when a muscle generates force while shortening, effectively bringing the origin and insertion closer together. In the case of the sternocleidomastoid during neck flexion, the muscle contracts to pull the head forward, facilitating the forward tilt of the neck.

As the sternocleidomastoid acts to flex the neck, it becomes shorter, demonstrating the characteristics of concentric contraction. This is essential for movements requiring the muscles to overcome resistance, such as lifting the head from a neutral position to bring it toward the chest. Understanding the nature of concentric contractions is critical for recognizing how muscles produce movement and generate force.