What is a stretch reflex?

A stretch reflex is a specific physiological response involving the contraction of a muscle when it is rapidly stretched. This happens as a protective mechanism to prevent injury. When a muscle is stretched quickly, sensory receptors known as muscle spindles detect the change in length and send signals to the central nervous system. In response, the nervous system sends a signal back to the muscle, prompting it to contract. This involuntary action helps maintain posture and balance and protects muscles from excessive stretching.

In this context, the other options do not accurately describe a stretch reflex. Voluntary muscle contractions are intentionally initiated by the brain, while a stretch reflex occurs without conscious control. Some methods may increase flexibility, but they do not illustrate the reflexive response of the muscle itself. Similarly, techniques to improve muscular endurance involve repeated contractions over time, which is unrelated to the immediate involuntary response characterized by a stretch reflex.