Functional Flexibility

When engaging in a passive hamstring stretch, not only are you excessively lengthening the hamstring, but you are training the hamstrings to disengage while in a lengthened position.

Functional Flexibility
by Michael Dugan
Aug. 15, 2022

Mobility is a word that is thrown around quite often in the fitness industry. Oftentimes, mobility is seen as a beneficial trait that should be trained as part of a good fitness routine. One person’s vision of mobility is being able to stretch into extreme ranges of motion, another’s is to simply be able to reach overhead and grab something off a shelf.

In this article we’re going to pose several questions about mobility or flexibility. First and foremost, what does functional flexibility actually look like? Can someone be too flexible? What are the ramifications of being too flexible? What parameters can we use to determine if a range of motion is beneficial or not so that we can continue to work out effectively?

Let’s first start by outlining what flexibility is and providing some context for our discussion.


What is Flexibility?

When many people think about flexibility, they envision being able to do something like touch their toes or do a split. What may not be considered, however, is the impact of the resulting flexibility on overall functionality of the human body.

Perhaps one of the issues with discussing flexibility, and why many are a bit confused about how to achieve it, is that the word flexibility is not very specific. This leads many people to partake in stretching routines with no particular goal in mind other than just increasing the ability to do a certain stretch.

What we want to discuss in this article is how much flexibility is enough, what clues do we have about what ranges of motion are beneficial, and how we should go about achieving them.

In order to provide more clarity to the discussion, we’re going to discuss functional flexibility in the context of our evolutionary blueprint as humans.


What is Hypermobility?

An abundance of scientific evidence suggests that the primary human movements are standing, walking, running and throwing while on two feet. It is our opinion that if something negatively impacts your ability to do these things, it is not contributing to the overall functionality of your human body.

Alternatively, if something supports your ability to perform these functions, it is truly functional by definition.

Therefore, ranges of motion that are similar to those applied in good standing, walking, running, and throwing  motions would constitute functional flexibility. Ranges of motion that are excessively outside of those found in these motions could contribute to hypermobility. That is, if they are achieved passively.

One example of this would be the classic hamstring stretch that is a common go-to stretch for many people. When we look at the motion of running, there is a certain amount of length and contraction that must occur on the hamstring in order to propel the body through space effectively. Looking at high-level sprinters would give a good clue as to what that range of motion could look like.

When engaging in a passive hamstring stretch, not only are you excessively lengthening the hamstring, but you are training the hamstrings to disengage while in a lengthened position.

Consequently, research has shown that stretching doesn’t improve running performance and may actually contribute to injury (S, S).

That’s not to say that going into deeper ranges of motion should never be done, but doing so passively seems to promote a loss of structural integrity within the body and a host of other negative effects.

So if during the motion of running you lengthen your hamstring by using other muscles to pull your leg into hip flexion, maybe the body is meant to create flexibility through movement? Or at the very least we should consider this as a different method to create flexibility.


Negative Consequences of Hypermobility

A 2012 study on 72 volunteers found that hypermobility was associated with an increase in anxiety (S). Additionally, the participants of this study were found to have enlarged amygdala. The amygdala is primarily thought to be involved with decision making and emotional responses. 

Another more recent study performed on 53 patients found that joint hyper-mobility was associated with a higher tendency to have an eating disorder (S).

Although we still need more research in these areas, a recent meta-analysis found that joint hypermobility may also have an influence on fibromyalgia, certain gastrointestinal disorders, and chronic fatigue (S).

Considering that many people partake in stretching as a means to achieve a more relaxed state, more caution should be taken to ensure that hypermobility is not created as this could have the opposite effect long-term. Generally, there seems to be a trend between hypermobility and dysregulation of the nervous system. 

So how do we create mobility but not hypermobility? It seems as though your body actually has a built-in mechanism for doing this called reciprocal inhibition.


Reciprocal Inhibition, How Functional Flexibility is Created

Reciprocal inhibition refers to how muscle groups work in opposition to each other. In other words, as one muscle shortens another lengthens. It is like a system of pulleys that are interconnected and work together to move your bones through space.

For example, if your bicep shortens, then your triceps must lengthen in order to allow that to happen. If your triceps did not lengthen, then you would not be able to flex your elbow.

This is an isolated example of reciprocal inhibition. There are integrated examples of reciprocal inhibition as well that apply to the entire body. For example, if you bend over to pick something up, you are lengthening almost all of the tissues on the back side of your body. Simultaneously, the majority of the muscles on the front side of the body are shortening. When you begin to lift that object off the ground, the back side of your body shortens as the front side lengthens.

Integrated reciprocal inhibition is how your body moves safely through space. When you move properly you contract and strengthen muscles while creating the exact amount of mobility you need to complete your motions.

The act of creating this mobility through integrated reciprocal inhibition is what allows you to improve flexibility without promoting hypermobility.

In static stretching practices, this protective mechanism is bypassed completely and allows the joints to be taken into unsafe ranges of motion.


Creating Functional Flexibility

To create functional flexibility we must consider the primary movements of humans and the concept of reciprocal inhibition. Off of this framework, we can develop methods to increase range of motion while making the body stronger and more athletic.

Additionally, these same concepts can be applied to achieve deeper ranges of motion in the body without promoting hypermobility.