Which of the following is the effect of spasticity when rapid limb movement occurs?

Spasticity is characterized by an abnormal increase in muscle tone or stiffness, which can lead to difficulty in controlling movement. When rapid limb movement occurs in a person with spasticity, a sudden release of resistance after brief resistance is commonly observed. This phenomenon is often referred to as the "clasp-knife response," where there is initial stiffness that suddenly gives way. This occurs because the neural pathways responsible for muscle tone are hyperactive, causing the muscles to resist movement initially, but they may not sustain that resistance as the movement velocity increases.

The correct answer highlights how spasticity can result in abrupt changes in resistance during rapid motions, which is essential for understanding the dynamics of movement in individuals with spasticity. This can impact physical therapy approaches and the management of spasticity in clinical practice, as recognizing this pattern can inform treatment strategies aimed at improving mobility and function.