Muscles are protected from over-stretching by several receptors that are located within the muscle itself and in the surrounding connective tissue.
One of the most important receptors that protect muscles from over-stretching is the muscle spindle. Muscle spindles are sensory receptors located within the muscle that detect changes in muscle length and rate of change of muscle length. When a muscle is stretched, the muscle spindle is activated and sends signals to the central nervous system, which in turn triggers a reflexive contraction of the muscle, protecting it from over-stretching.
Another receptor that plays a role in protecting muscles from over-stretching is the Golgi tendon organ. Golgi tendon organs are sensory receptors located at the junction of the muscle and tendon. They detect changes in tension within the tendon, and when the tension becomes too great, they send signals to the central nervous system, triggering a reflexive relaxation of the muscle. This protective mechanism prevents the muscle from being subjected to excessive force that could result in injury.
Both the muscle spindle and the Golgi tendon organ are important for maintaining muscle integrity and preventing injury during physical activity.