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Flexibility occurs when the muscles around a joint are able to change their length. The more change in length, the greater the flexibility. For a joint to move through a large range of motion some muscles need to dramatically lengthen while the opposing muscles need a corresponding amount of shortening.

When we talk about increasing flexibility it is important to understand what is actually changing in the body to create more dynamic muscle variability.

The Most Common Myth About Flexibility

The most common myth is that increased flexibility comes from actually making a muscle longer so that it can stretch farther. The truth is that this kind of structural change accounts for a very small percentage of any increase in flexibility.

If your straight leg hamstring stretch starts at 40 degrees and, after a month of regular flexibility training, you are able to reach 60 degrees of flexion, that does not mean that your hamstring muscle length has increased by two to four inches. Muscles do not change in length at that rate.

Nor does the change come from increasing the length of tendons or ligaments. Some change in fascial structures may account for easier movement, especially when you are able to break up adhesions or old scar tissue that is gumming up the free movement of joints and muscles. However fascia is not elastic, and over-stretching tendons and ligaments can cause injuries and long-term joint instability so this is not where you want to get your increased mobility.

The truth is that almost all flexibility gains are neurological.

Flexibility is in Your Head

No muscles, no matter how strong or buff, are able to contract without a signal from the nervous system. Nor are they able to relax without permission from that same system.

In order to understand flexibility, let’s start by looking at it’s opposite: tightness.

Tightness can certainly come from the stiffness of short, dense muscles or gummed up fascia. But most of the time the tightness that plagues us in our daily lives, keeps us from our flexibility goals, and causes pain and imbalances, is a result of our brain’s relationship with our muscles.

The subconscious reflexes that keep us safe govern the level of tone (how much a muscle is contracted) in our muscles. When our brain decides that we are safe and our risk of injury is low, it allows our muscles to relax.

A relaxed muscle is better at lengthening and contracting than a tense muscle. Muscle tension does not indicate strength, it indicates stress.

A tense muscle will not have the same access to range of motion as a relaxed muscle. Therefore the way that our nervous system’s perception will dictate how much range we have in a given stretch much more than any structural changes to muscles or fascia.

How do we Use the Brain to Train Flexibility?

When we are increasing our flexibility we are using tools that change our nervous systems’ perceptions about that increased range.

The vast majority of stretching techniques are primarily affecting the nervous system. Static passive stretching, dynamic and active techniques, resistance techniques like PNF or PIR, even some myofascial techniques like foam rolling all have a heavy neurological impact.

It is only once the nervous system has successfully adapted to flexibility training that changes can be made to muscle length. Most people outside of contortionists, gymnasts, and dancers do not ever need to actually lengthen the muscles in order to reach their flexibility goals.

Multiple studies, like this one published in the Physical Therapy Journal in 2010, confirm that the changes made by training flexibility over the short and medium term were almost entirely due to “modifying sensation”. The body stopped fighting the range.

Over the coming month I’m going to continue to explore, in more detail, the nervous system functions that govern range of motion and how different flexibility training techniques impact those functions. My hope is that this will enable you to make informed decisions about your own training and understand what is going on with your body when you stretch.

My greatest goal is to enable us humans to approach training as a partnership with our body and nervous system, not as a tyrant. Physical changes, particularly flexibility, are so much more sustainable and healthy when we understand what we are doing and why. This also makes it easier to address sticking points and, I hope, more compassionate for our bodies when they don’t respond the way we want.

Got questions? Just ask!

Happy Bendings,

Kristina