What happens to muscle tissue when it is not used over a long period?

When muscle tissue is not used over an extended period, it undergoes atrophy, which is the process where muscle fibers decrease in size and mass. This typically occurs due to disuse or lack of activity, leading to a reduction in the workload that muscle fibers experience. The muscle cells adapt to this decrease in demand by reducing their size, as the body prioritizes energy efficiency. Atrophy can result from various factors, such as immobilization, prolonged bed rest, aging, or diseases that affect muscle function.

Hypertrophy, which is an increase in muscle size, typically occurs in response to regular exercise and resistance training, as the muscle fibers adapt to increased load. Cell death is a more severe phenomenon that can occur due to injury or diseases and is not directly related to disuse. Similarly, an increase in strength would usually require exercise and physical activity, counter to the effects seen in atrophy. Therefore, the only correct answer that describes the consequence of disuse in muscle tissue is atrophy.