What does rigidity indicate in terms of muscle tone?

Rigidity indicates increased muscle tone that persists throughout the range of movement. This condition is characterized by a resistance to passive movement that remains constant regardless of the speed of that movement. Unlike spasticity, which may vary based on the speed or direction of movement, rigidity does not change, marking it as a distinct feature in conditions such as Parkinson's disease. This constant resistance can lead to stiffness and difficulty in initiating movement, making it a critical aspect to assess in clinical settings when evaluating neuromuscular function.

In this context, the other options do not accurately describe rigidity. A decrease in muscle tone would suggest hypotonia, which is not reflective of rigidity. Normal muscle tone would imply a balanced state, while intermittent muscle fluctuations refer to conditions where tone varies, neither of which applies to rigidity's consistent and elevated tone response.