What is the primary characteristic of myalgia?

Myalgia is defined as pain in the muscles. The primary characteristic of myalgia is indeed the discomfort or pain felt within the muscle tissue, which can vary in intensity and may be accompanied by other symptoms depending on the underlying cause. This type of pain is often associated with various conditions, such as overuse, injury, infections, or systemic diseases. Recognizing muscle pain as the hallmark of myalgia is critical for diagnosing and managing related health issues.

In contrast, the other options relate to different conditions and symptoms that are not specific to myalgia. For instance, swelling in joints pertains to conditions like arthritis, red skin could indicate inflammation or allergic reactions, and fluid accumulation might relate to edema, which has its own distinct causes and implications. These symptoms do not directly describe myalgia, further emphasizing that muscle pain is the defining feature.