Which type of increased muscle tone is velocity dependent and worsens with extremes of ROM, typically seen with corticospinal tract lesions?

• A. Rigidity
• B. Dystonia
• C. Spasticity
• D. Flaccidity

Answer: (C)

Spasticity is the type of increased muscle tone that is velocity dependent and worsens as you move a joint toward its end range. It arises from disruption of descending inhibitory pathways from the cortex to the spinal cord (an upper motor neuron, corticospinal tract lesion), which makes the stretch reflex more excitable. Because the resistance increases with faster passive movement and at extreme ranges of motion, it’s typically seen with UMN injuries.

Rigidity, by contrast, is a constant resistance to movement that does not depend on the speed of movement and is more characteristic of Parkinson’s disease. Dystonia involves involuntary, sustained muscle contractions causing abnormal postures or twisting, not a velocity-dependent increase in tone. Flaccidity is decreased muscle tone, not increased. Signs often accompanying spasticity include hyperreflexia and clonus, reflecting the reflex hyperexcitability from corticospinal tract disruption.