Which condition is characterized by prolonged, involuntary muscular contractions?

The condition characterized by prolonged, involuntary muscular contractions is muscle cramps. Cramps are typically defined as sudden, involuntary muscle contractions that can often be intense and last for varying durations. They usually occur in specific muscle groups and can be caused by factors like dehydration, electrolyte imbalances, overuse, or muscle fatigue.

In contrast, the other conditions mentioned involve different issues. Bursitis refers to the inflammation of the bursa, a small fluid-filled sac that acts as a cushion between muscles, tendons, and bones, typically causing pain and limited movement in the affected area but not specifically sustained muscle contractions. Fibromyalgia is recognized as a chronic condition that causes widespread pain, fatigue, and tenderness, often leading to a general state of discomfort rather than specific muscle contractions. DJD, or degenerative joint disease, involves the degradation of joint cartilage and underlying bone, which can lead to pain and stiffness in joints but does not entail the involuntary muscular contractions that define cramps.

Thus, the defining characteristic of muscle cramps emphasizes the prolonged, involuntary contractions, making it the correct answer to the question.