When most people think of flexibility, they picture someone like a dancer, a gymnast, or a yogi - someone who can easily move their body into deep-looking shapes like full forward splits (hanumanasana) or yoga’s king pigeon pose (ekapadarajakapotasana). But most people are operating under an incomplete definition of what it means to be flexible. Flexibility doesn’t simply mean the ability to take your joints through great ranges of motion, regardless of what tissues stretched to get you there. We’re lucky enough to have a growing movement in the yoga world today that seeks to update our traditional understanding of yoga with the grounded scientific knowledge of biomechancs. As a cornerstone of that movement, we need to make sure we understand what true flexibility means and how it’s different from a term that many people mistakenly conflate with flexibility: hypermobility.
HYPERMOBILITY VS. FLEXIBILITY
Here’s the deal: the term flexibility refers to muscles (and their associated fascia) while the term hypermobility refers to ligaments. Muscles and ligaments are two distinct types of tissues which perform very different functions in the body. Here’s a quick anatomy primer (it's a bit oversimplified, but still helpful!):
A muscle is a contractile tissue which crosses over one or more joints in your body. When a muscle contracts, it exerts a pulling force on the bones to which it attaches. Ligaments, on the other hand, are short bands of fibrous connective tissue which connect bone-to-bone and effectively “fasten” our joints together. Unlike muscles, ligaments don’t contract, generate force, or create movement in the body. Instead, as my biomechanics teacher Katy Bowman says, the ligaments serve as the “seat belts” of our joints. They can be considered our built-in back-up system to stabilize our joints if our body moves in a way that would otherwise take a joint beyond its normal range of motion.
SHOULD WE STRETCH OUR MUSCLES OR LIGAMENTS?
When we stretch, our intention should be to elongate our muscles and not our ligaments. When muscles stretch, they return to their original length after the stretch is released - a tissue property called elasticity. But when ligaments stretch, they behave elastically during just the first tiny bit of the stretch, and if they’re stretched beyond that point, they will permanently stay at that new length and are referred to as lax. Lax ligaments can no longer stabilize our joints for us and are a source of chronic pain and injury for many people. Overstretching our ligaments is therefore decidedly uncool.
Although many people have been told that they’re “hypermobile”, only a small percentage of the population actually has a condition of generalized, all-over joint hypermobility. In reality, most people who think of themselves as “hypermobile” simply have a specific number of joints whose ligaments have become lax. That ligament laxity is usually the result of the joint being habitually loaded beyond its normal range of motion, which is what happens when we “flop into our joints” time-and-time again without muscular support. Once you have the ability to hyperextend a joint, you will always have that ability, because you can’t “stiffen” your ligaments back up once they’ve become lax.
Here's a visual example of what hypermobility looks like when it happens at the elbow joint, a common site of too much mobility in yogis (including me!)
Here are my nice elbows at their healthy normal end range of motion in extension: 180 degrees.
And here are my same elbows at beyond 180 degrees. These elbows are no longer within the normal range of motion for extension. They’re in hyperextension, which is an unhealthy, unstable place for them to be. For the health of our joints and therefore our whole body, we need to work to keep our joints out of hyperextension as much as possible.
HYPERMOBILITY = LACK OF FLEXIBILITY (SAY WHAT?)
As surprising as it sounds, hypermobility goes hand-in-hand with tight muscles. In fact, many people develop hypermobility in their joints in the first place as a result of tightness in muscles close to that joint. Additionally, one classic rule that our bodies tend to follow is that they prefer to move via “the path of least resistance”. It’s always easier to move your body where you’re already mobile and have less resistance than a place that is stiff and unyielding. Therefore, if a person with lax ligaments attempts to stretch her/his actual muscles, their clever body will sneakily rearrange itself into familiar and easy hypermobility land (the aforementioned path of least resistance), thereby bypassing the intended muscular stretch and loading the ligaments instead. Unless we learn how to override this tendency of the body with intelligent alignment, our stretches will result in joints whose hypermobility is reinforced and muscles that weren’t stretched at all, every time we stretch. And who wants that?
HYPERMOBILITY MASKING AS FLEXIBILITY
This last point is possibly the most important one of this entire article (and maybe of this whole blog!) Many poses in the practice of yoga require great ranges of motion from our bodies. In fact, there are quite a few asanas which can’t be performed to their fullest expression without our joints exceeding their normal range of motion. Put another way, many yoga poses require hypermobility in order to achieve.
Let’s examine full king pigeon pose (ekapadarajakapotasana), a pose we mentioned earlier in this post. This is an undeniably aesthetically-pleasing, graceful asana, and when we see someone doing it, we often think, “Wow, look at how flexible that person is!”
But remember what we’ve learned about the difference between flexibility (muscles) and hypermobility (ligaments)? Despite the fact that this pose is so pretty that it has graced the cover of Yoga Journal on many occasions, the biomechanical truth of this asana is that it cannot be achieved unless the low back (lumbar spine) moves into a high degree of hyperextension, which you can probably see if you look closely at this yogi’s lower back area. The normal range of motion for extension of the lumbar spine is somewhere between 20-35 degrees, but this yogi’s lumbar spine has extended far beyond that amount, creating compression and degenerative forces in this vulnerable area of the body. In addition, the fact that the lumbar spine is in such an extreme arc in this pose means that the yogi is able to bypass stretching her tight hips and shoulders. A general rule of thumb for working with the body is that we want to stabilize where we’re too mobile and mobilize where we’re too stable. But in this pose, we’re doing the exact opposite, allowing our tight spots to remain tight and our overly mobile spots to become more mobile and therefore more unstable.
It’s not enough to approach our yoga poses as “stretches”. We need to consider where the stretch is taking place and what tissues are stretching to make the shape happen. A yogi performing full king pigeon pose might look flexible, but the truth is that although she has moved her body through a great range of motion, it’s hypermobility, not flexibility, that allowed this motion.
I'm excited to be part of the growing movement within the yoga community that seeks to merge our grounded scientific knowledge of the body with our understanding of yoga. And as a cornerstone of this movement, we need to make a very clear distinction between what is flexibility and what is hypermobility, and use that understanding to make informed decisions about which asanas we choose to practice and why. My goal in my yoga practice and teaching is cultivating the long-term health and well-being of our bodies, our body-mind connection, and our lives as a whole, and this goal is contingent on emphasizing true flexibility and downplaying hypermobility as much as possible in our practice.