Stretch Your Knowledge: The Stretch Reflex

Success is due to our stretching to the challenges of life. Failure comes when we shrink from them.

          – John C. Maxwell

The physical aspect of yoga is all about breathing, strengthening, and stretching. During a stretch there is communication between the nervous and muscular systems, resulting in a natural stretch reflex. The stretch reflex protects our muscles and connective tissues from being placed under too much force, which can lead to injury. This reflex naturally limits how far we can stretch a muscle. However, by understanding how this reflex works, we can apply different techniques to create more muscle relaxation and a deeper stretch.

The two types of stretch reflexes we will focus on are the myotatic reflex and PNF. (PNF is one of the most effective techniques for deepening a stretch. We’ll explore it in detail in the next post.)

Recall in the last post the relationship between the agonist and antagonist muscles involved in movement. The agonist muscle is the muscle being contracted to create movement. The antagonist muscle is the muscle that relaxes and stretches to allow for movement to occur. Our focus is to relax the antagonist muscle effectively to allow for deeper stretching. This is where we can either work forcefully against the limitations of the stretch reflex (increasing the potential for injury) or use our knowledge of the stretch reflex to safely and gradually move deeper in a posture.

How the Stretch Reflex Works

The myotatic reflex, more commonly referred to simply as ‘the stretch reflex’, is a response between stretch receptors and nervous system. Muscle spindles are tiny organs located within muscle fibers that are very sensitive to changes in muscle length. As a muscle is lengthened, the muscle spindles send a signal to the spinal chord that sends a command back to the stretched muscle to contract. Another response is also sent to the opposing muscle (the agonist) to relax.

This communication is so fast that it does not even need to reach the brain, only the nerves in the spinal chord. This is called a feedback loop as information constantly ‘loops’ between the muscle spindle receptors and the nerves in the spine without having to be sent to the brain for processing.

This reflex is occurring all of the time. Take standing upright for example. After standing for a period of time, many people start to lean to one side. Muscles near the spine will react to their new stretched state by contracting, pulling the body upright to a state of better posture.

The strength of the contraction response is relative to the weight and speed (force) behind the movement. Imagine walking and slipping on some ice. As a lot of weight starts to fall on your suddenly outstretched leg, your body naturally contracts the stretched leg strongly to prevent tearing in your now vulnerable muscles and connective tissues.

Now imagine waking up from a deep sleep and slowly stretching your arms overhead. With less weight and less speed involved in the movement, there is much less force. As a result, the contraction response is relatively weak and we don’t notice our body contracting or tensing up for protection.

Static and Dynamic Elements

The stretch reflex is composed of a static and dynamic element. The static element is active the entire time that the muscle is being stretched. There is nothing we can do to eliminate this component of the reflex.

The dynamic element of the reflex is strongest at the onset of stretching a muscle. When we initially stretch a muscle, the change in length is more sudden and triggers a more powerful response. (If we stretch a muscle very quickly, the center portion of the muscle will absorb most of the stretch first to protect the connective tissues at the ends.) As the rate of change in muscle length decreases over time, the dynamic component of the reflex starts to back off. As more sarcomeres are allowed to relax, the overall muscle can lengthen further.

Applying This Knowledge to Asana

Now imagine coming into paschimottonasana: seated forward bend. (Or better yet take a minute after reading this and give it a go!)

paschimottonasan

Taking your time, you slowly move a tiny bit deeper on each exhalation (lengthening with each inhalation). As your hamstrings are in a lengthened state, some fibers within the hamstring will contract due to the stretch reflex. But since you are progressing gradually deeper, there is less speed and therefore less force behind the movement. Thus the contraction response is not very strong. In fact, over time more of the fibers that have been recruited to contract will relax, allowing the muscle to lengthen further.

By moving slowly with our breath and staying in a posture for a longer period of time, we can deepen the stretch in any posture. When our muscle fibers are held in a stretched position for a longer time, our muscle spindles become accustomed to the new length. Once accustomed to the new length, many muscle spindles (the dynamic component) will start to reduce their signals for contraction. It is even possible to train our stretch receptors to allow greater lengthening of the muscles. This can result from maintaining a regular stretching practice over an extended period of time.i

Our bodies are constantly adapting to how we use them to interact with our world. Simply slowing down from our overactive daily lives can have profound effects. So take your time, breathe deeply, be mindful, and enjoy finding new depths in your physical, mental, and spiritual self.

ihttp://web.mit.edu/tkd/stretch/stretching_2.html#SEC15

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