Which of the following is NOT a type of muscle fiber?

The correct answer is elastic, as it is not classified as a type of muscle fiber. In the context of muscle tissue, there are three primary types of muscle fibers: skeletal, cardiac, and smooth.

Skeletal muscle fibers are under voluntary control and are attached to the skeleton, allowing for movement. These fibers are striated and facilitate activities like walking or lifting. Cardiac muscle fibers are found exclusively in the heart and are responsible for pumping blood throughout the body. These fibers are also striated but operate involuntarily. Smooth muscle fibers are found in the walls of hollow organs, such as the intestines and blood vessels, and are responsible for involuntary movements, such as digestion and blood flow regulation.

Elastic refers to a property of certain tissues and materials that can stretch and return to their original shape, but it is not a classification of muscle fiber. Therefore, the identification of elastic does not fit within the context of muscle fiber types.