New science reveals to us a model of stretching that is much more complex, dynamic and fascinating than what we’ve previously imagined.
A new paradigm of flexibility
Biomechanics-based Restorative Exercise™ teaches a lot of new and eye-opening information about stretching and flexibility that isn’t yet common knowledge in the yoga world. Additionally, the wonderful yoga teacher Jules Mitchell is on a mission to educate the yoga community about the science of stretching. Her recently-completed master’s thesis in exercise science is a comprehensive literature review of the most current scientific research on stretching to date, and it’s full of an abundance of important information for yogis.
Utilising the innovative knowledge that these resources offer, let’s examine some of our current beliefs about stretching and introduce some helpful ways we can begin to update these beliefs to reflect the newest scientific word on the street.
What we think happens when we stretch
Most people think of their muscles as being either “long” or “short”, and that during a stretch, they are targeting their “short” muscles by physically “lengthening” or “loosening” them. In this stretching paradigm, our muscles are mold-able tissues like taffy or play-doh which we can form into a shape of our choosing by simply pulling or pushing on them. For example, when we fold forward into paschimottanasana (seated forward fold), we tend to imagine that our hamstrings are physically growing longer in that moment of our stretch in the same way that taffy would grow longer if we tugged on both of its ends for awhile. We imagine that when we release paschimottanasana, our hamstrings remain just a bit longer than they were before we did the stretch. And we also imagine that the longer and deeper we hold a pose like paschimottanasana, the longer and looser our hamstrings become.
This stretching paradigm is what most of us were taught in our yoga classes, workshops, and teacher trainings. It’s completely understandable that we might see the body as working like this, but new research is revealing a very different version of the biomechanics of stretching.
The new science of what happens when we stretch
We all know that when we stretch, we experience a feeling of “tightness” at our end range of motion – a sensation that limits us from moving any deeper into the stretch. We have traditionally defined this “tight” sensation as the result of having reached the end length of the muscle(s) we’re stretching. In other words, we pulled on the ends of our muscle until we reached its maximum physical length, and once we hit that boundary, the stretch stopped and we felt the “tightness”. With enough stretching, we could increase the length of our muscle and therefore move further into our stretch with time.
But we now understand that increasing our flexibility has much less to do with the physical length of our muscle tissue, and much more to do with the part of our body that controls and moves our muscles: the nervous system. Our brain, the main control center of our nervous system, is in constant communication with our muscles and one of its main imperatives is to keep our body where it perceives it is safe. Normal movements that we make throughout our day are considered safe by the brain because it knows and trusts them. But on the other hand, our brain is not familiar with ranges of motion that we never move into, so it’s much less likely to consider those places safe. When we stretch, if we move into a place that the brain isn’t familiar with, our nervous system will end our stretch by communicating with our muscles to put the breaks on the movement.
For example, if you happen to work on your computer for 8 solid hours a day (and if you don’t take frequent intermittent stretch breaks for your shoulders – hint hint), the brain becomes very familiar with the arms-forward position that you use while typing and considers that range safe. Then later, if you decide to do a chest stretch in which you take your arm out to the side and then behind you, the brain doesn’t feel that that movement is safe because you so rarely go there, so it will limit your range very early on in the stretch.
A major takeaway from this new flexibility paradigm is that when we increase our range of motion through stretching, it isn’t because we pulled on our tissues and made them longer. It’s because we visited the edge of our stretch (also called stretch “tolerance”) enough times that our brain started to feel comfortable there and it began to allow us to move deeper into that range.
Okay, I think I’m starting to get it, but why is this so important?
It’s definitely interesting and more scientifically accurate to understand this previously-overlooked role that our nervous system plays in flexibility. But whether it’s your nervous system or the physical length of your muscles limiting you in a stretch, why does it matter? Isn’t a stretch a stretch, regardless of the mechanism behind it?
That’s a great question – I’m so glad you asked! The main answer has to do with what tissues are being targeted when we stretch. We often think and talk about stretching our muscles in our yoga poses (i.e. paschimottanasana stretches our “hamstrings”), but in truth our muscles are surrounded by, interwoven with, and inseparable from our fascia. Our fascia is our incredible body-wide web of connective tissue that is literally everywhere inside of us, and it includes our tendons and ligaments. Muscles and fascia are two distinct tissues with different properties, but both are affected when we stretch. And how we choose to stretch, which is based on whether we believe that we’re physically lengthening our muscles (old paradigm) or increasing our nervous system’s tolerance for the stretch (new paradigm), determines how our fascia will be affected during the movement.
What does pulling hard on our tissues achieve?
In the old paradigm of stretching in which we believe that we’re physically pulling our tissues longer like taffy when we stretch, it would logically follow that in order to gain more flexibility, we should simply pull harder and deeper. Wringing oneself deep into a spinal twist or receiving a strong adjustment from a teacher intended to push your range of motion further are common examples of this strategy. But we now understand that flexibility is much less about using brute physical force to grow our muscles longer, and much more about using intelligent communication to suggest to our nervous system that a particular range of motion is safe.
In fact, the “brute force” method of stretching is problematic in multiple ways. When we stretch, our muscles aren’t the only tissues that are affected. Muscles are surrounded by and interpenetrated with fascia, which also makes up the body’s ligaments and tendons. When we move our body into a stretch, both our muscles and our fascia experience the stretch at the same time.
It’s important to understand that fascia has only a set range that it can stretch. Stretching offers many benefits to the health of our fascia, but it won’t change the range of this tissue. This means that after fascia experiences the load of a stretch, only one of two possibilities can happen: 1) it returns to its original length after being stretched or 2) it is stretched too far and is damaged. And that’s it! We don’t make our fascia “longer” when we stretch. And if we pull too hard on this tissue in an effort to elongate it, we will most likely move beyond its ability to withstand the load, which will ultimately lead to injury. As counterintuitive as it may seem, for the health and balance of our structure, we actually want our fascia to be quite “stiff” and “resilient”.
But how much stretch is the right amount?
We understand that stretching intensely does not benefit us, but how do we know where that boundary lies in our body? Here’s a key rule to use in your practice: when we stretch, we should only move into a range of motion over which we have muscular control. This is because our nervous system feels safest when it senses that we have control over our movement.
Put another way, we don’t want to create flexibility without the strength to support it. If we stretch within these parameters, our practice is likely to contribute to a balanced body that moves well. However, when we stretch into a range in which the targeted muscles cannot function, we are creating excessive mobility (and more than likely ‘hypermobility’) that we don’t have the ability to stabilise.
To illustrate this point, think about at hanumanasana, yoga’s forward splits. If we practiced that pose with the goal of building flexibility within the context of strength, we would only move as deep into the shape as the muscles of our legs could maintain control. Picture it: without using your arms pressing into the floor, you would slowly lower down into your full hanumanasana and then use those very same leg muscles to lift yourself all the way back up (again, without the use of the arms!) This might seem like a superhuman acrobatic feat, but I promise it would be possible if you truly worked to build power at your end range.
Let’s touch in on a few other asanas to see how this “stability at your end range” principle might apply. Padmasana, or lotus pose, is one of yoga’s classic asanas. Most of us use our arms to pull our legs into this shape. We also sometimes use momentum to quickly fold our legs into lotus, but momentum is another method of moving into a range of motion that we don’t have the strength to control. Is it any wonder that padmasana is notorious for tearing soft tissue in many a yogi’s knee joint? Try this instead: without using your arms for momentum, use only the muscles of your legs to fold your feet as close to your hips as you can and breathe there. This shape – one over which your muscles have control – is the correct stability edge for your body. Another great example is ekapadasirsasana, yoga’s leg-behind-the-head pose. If that leg can climb behind your head itself, without the use of your arms, then you’re staying within your excellent strength-at-your-end-range limits. But I have yet to see a yogi who can accomplish such a daunting task! A less obvious pose in which we commonly move beyond our stability edge is gomukasana, or cow-face arms. Many people like to use their opposite arm to help that bottom arm climb higher up the back, but as soon as we interfere with that bottom arm’s own ability to move itself to its edge, we are stretching past our active range of motion and into unsupported mobility.
I know that so many of us yogis are used to going as deep as our bodies will allow in our poses. Think of the innumerable beautiful photos that yoga teachers have in their portfolios or on Instagram of their bodies looking extremely graceful in a perfectly-executed forward split.
The science behind utilising stability as a container for flexibility is not yet widely understood in the yoga world – and not surprisingly, the number of over-stretching injuries in our community is quite high. But as a yoga community, we have to ask ourselves some tough questions: if you have the mobility to move deeper into a pose than your muscles can control, where is that mobility coming from, what is it offering you in terms of how well your body functions, and how many more times can you practice this pose before an injury occurs? What is the value of flexibility without the strength to support it? This is the kind of shift in thinking that yogis needs to make if we want our practice to truly offer the structural health and other long-term benefits like ageing with ease that so many yoga practitioners seek.