Which of the following is a cause of muscle atrophy?

Muscle atrophy refers to the reduction in muscle mass and strength, which occurs when muscles are not used or are subjected to prolonged periods of inactivity. This phenomenon can result from a variety of factors, but prolonged inactivity or immobilization is one of the most significant causes. When muscles are not engaged in regular activity, such as during bed rest, injury, or other forms of immobilization, the body begins to break down muscle tissue at a faster rate than it is built up. This leads to a decrease in muscle size, which can have various negative effects on strength, mobility, and overall health.

In contrast, regular cardiovascular training actively engages the muscles and can help prevent atrophy by promoting muscle use and maintenance, while excessive hydration does not have a direct relationship with muscle atrophy. Additionally, improper warm-up routines, while they may contribute to injuries or reduce workout effectiveness, do not cause muscle atrophy in the same way that prolonged inactivity does. Therefore, the option highlighting prolonged inactivity or immobilization accurately identifies a key factor in the development of muscle atrophy.