What is the main difference between spasticity and rigidity?

• A. Spasticity is velocity and direction dependent
• B. Spasticity is not velocity dependent
• C. Rigidity is velocity dependent
• D. Both are identical across ROM

Answer: (A)

The main idea is that spasticity is a velocity-dependent increase in resistance to passive movement, while rigidity is a constant increase in tone that does not depend on how fast you move the limb. Spasticity arises from an upper motor neuron lesion, which makes the stretch reflex hyperactive. As you move a limb more quickly, the reflex kicks in more strongly, so resistance rises with faster stretches and you may even feel a brief drop in resistance (the clasp-knife phenomenon). Rigidity, seen in conditions like Parkinson’s, comes from basal ganglia dysfunction and produces a steady increase in tone throughout the range of motion, present whether you move slowly or quickly, and in both directions of movement. To test it, compare slow versus fast passive movement: if resistance increases with speed, that points to spasticity; if resistance stays roughly the same regardless of speed, that points to rigidity. Some clinicians also note that spasticity can be more pronounced in certain directions due to the pattern of neural involvement, but the defining feature remains velocity dependence.