Which terminology is used to describe a condition of increased muscle tone dependent on the speed of movement?

The condition characterized by increased muscle tone that varies depending on the speed of movement is known as spasticity. Spasticity is commonly associated with upper motor neuron lesions and is manifested as an abnormal increase in muscle tone, which can lead to resistance when attempting to move a muscle. Notably, the key characteristic of spasticity is that the resistance to passive movement is greater with rapid movements compared to slow movements. This phenomenon stems from an exaggerated stretch reflex due to altered neural pathways.

In contrast, rigidity describes a state of constant muscle tone and resistance that does not change based on the speed of movement, typically associated with conditions like Parkinson’s disease. Pseudohypertrophy refers to the enlargement of muscles, often observed in certain muscular dystrophies, where muscle fibers are replaced by fat and connective tissue, but it does not pertain to muscle tone. Flaccidity is characterized by reduced muscle tone and weakness, typically following lower motor neuron damage, which is opposite to the increased tone seen in spasticity. Thus, spasticity is the term that correctly defines the condition of increased muscle tone dependent on movement speed.