A stretch reflex, also referred to as a deep tendon reflex or myotatic stretch reflex, is the muscular response to stretching. When the muscle is stretched, the muscle spindles also stretch. Muscle spindles are the receptors within the muscle which detect a change of length. These receptors send a signal to the central nervous system, the brain and spinal cord, to regulate the contraction. The stretch reflex is activated to resist this lengthening which causes the large muscles surrounding the area contract or tighten. Sudden stretches cause a stronger reflex.

The stretch reflex is a protective response to avoid injury to the muscles by limiting the amount of lengthening. It also helps regulate and maintain muscle tone. Muscle tone is the continuous contraction of muscles which allows the body to maintain positions and posture.

There are two stages of a stretch reflex. The static reflex occurs as long as the muscle is being stretched. The dynamic reflex is the initial response to the stretch. A dynamic response lasts only a few moments but can be very powerful to protect the muscle from injury. The reflex diminishes as the tension is released.

When a muscle is working at an optimal length, contractions become more efficient. Stretching is important to maintain proper muscle length and avoid injury and pain conditions. It also aids in the removal of toxins and wastes from the muscles while increasing the circulation and supply of oxygen and nutrients the muscles need to work effectively. Stretching should be performed before and after physical activities, but can be beneficial to minimize morning stiffness and decrease daily tension before bedtime. It can also help release muscular tension buildup to decrease things like muscle spasms which can increase pain symptoms.

Improper stretching techniques can elicit a stronger stretch reflex. Stretching beyond capabilities or performing a stretch too fast can enhance the muscle’s protective reaction. This can increase the chances of injury to the muscle. Bouncing with stretch can also increase this response.

Though the stretch reflex is a defense mechanism, it can be used to enhance flexibility. Holding a stretch beyond this protective mechanism can enhance muscle lengthening. Increasing the time of stretch and allowing the stretch reflex to relax also encourages the surrounding musculature to benefit from this lengthening, thus providing a overall increase in flexibility of the muscle group. Once this reflex relaxes it is possible to stretch the muscle a little further to optimize muscle elasticity and range of motion.