Which of the following best describes atrophy?

Atrophy is best described as a reduction in size or functionality, which refers to the loss or wasting away of muscle tissue or other types of cells and structures within the body. This can occur due to various reasons, such as disuse, aging, denervation, or disease processes. When atrophy occurs, the affected muscles or tissues diminish in mass, which can lead to decreased strength and functionality.

The other options focus on opposite concepts. Increased muscle strength indicates growth or improvement, while improvement in movement coordination suggests enhanced function and efficiency of physical movements. Lastly, growth of new neurons refers to neurogenesis, which is the process of creating new nerve cells—an entirely different physiological occurrence than atrophy. Thus, the definition that aligns with the characteristics of atrophy is the reduction in size or functionality.