Throughout our lives, most of us have heard that it is extremely important for us to be “flexible,” for a variety of reasons. Off the top of my head, I’ve been told that flexibility is important to make movement easier, so that my joints don’t deteriorate, and so that I don’t get hurt lifting heavy objects. This is excellent advice. But the problem is that basically all of us go about achieving greater flexibility in exactly the wrong way: by stretching, or more specifically, static stretching. And that is because we don’t understand the concept of flexibility in a mechanically useful way.

One of the main physiological problems of westernized people is poor biomechanics—a phemonemon that basically boils down to the idea that the muscles across our bodies are badly synchronized. Simply stated, they don’t know how to work well together, and when they are subjected to trying circumstances (such as exercise or age), the mechanisms freeze up and become damaged.

For some non-athletes, stretching may help initially. In a very low-risk environment, stretching helps these frozen mechanisms because it increases the net joint range of motion (ROM). This means that the joint can go just a little more before it gets hurt. But that doesn’t solve the problem: the muscles haven’t become synchronized; we’ve only ameliorated the symptoms because we’ve created ROM by isolating the muscles (due to stretchier tendons and weaker muscles), instead of developing their synchronization.

This is a classic case of a systems management problem called “shifting the burden.” We have a perceived need to increase flexibility (because of a particular set of assumptions), and we shift the burden of flexibility away from synchronization and towards isolation. When the symptoms ameliorate, we think that the problem is solved, and we subject it to higher-risk circumstances, such as sports. Soon, we find ourselves caught in an unending roller-coaster of injury.

We can solve this problem. But in order to do so, we must deconstruct our notions of “flexibility.”

Let’s first establish the typical definition of flexibility. According to an excerpt by Human Kinetics (a very reputable source—publisher of Developing Speed, which I’ve  quoted from before), “flexibility” is:

“A measure of the range of motion around a joint (e.g., knee) or series of joints (e.g., lower back). Flexibility is most limited by the joint’s physical structure, including the bone, connective tissue, and muscle.”

Most of us approach flexibility training with the following assumptions: that it is good to have more flexibility, and that flexibility is, as stated above, a measure of joint ROM.

These assumptions typically lead us to make the most obvious intervention we can make, with the purpose of increasing ROM: stretching the joint tissues to overcome the stretch reflex, and teach the muscles to relax. Once they’ve relaxed, we can make the tissues “give” and lengthen over time. According to Dr. Phil Maffetone, who I’ve quoted before, this is a very bad idea, especially for runners. An array of scientific studies have found either no benefits to stretching, or explicit risks to static stretching.

We athletes, particularly those of us who don’t need extreme ranges of motion (such as runners), should immediately stop stretching, get the facts, and share them with others.

Arguably the most important part of the running stride for both speed and injury prevention—(these things tend to go together)—is cadence. In order for the body to maintain cadence, there must be very specific tension patterns in the muscles and tendons across the body.

For example, in order to swing the leg forwards after toe-off to take the next step, it is critical that the achilles and hamstring tendons remain taut during the stance phase, so that they can recoil as soon as the toe lifts of from the ground, flexing the knee and allowing the leg, which has now been brought up against the hip, to snap forwards.

In order to achieve this tautness of the hamstring and achilles tendons, the leg muscles must contract reflexively—it is the stretch reflex that allows the tendons to remain taut. If we train ourselves to “beat” the stretch reflex (which is an important component of stretching), we will see the tension patterns collapse, and our cadence plummet. Our speed and power, as well as health of our tissues and joints will become compromised.

But here’s the kicker: we can’t allow our tendons to become too long or too loose either—if we do, no amount of stretch reflex is going to make the tendons taut and allow us to maintain cadence. We need stiffer tendons to run better. In other words, everything that static stretching does is bad for a runner.

In other words, given the assumptions that we usually bring to the table, the notion of flexibility put forth by Human Kinetics may be accurate, but it is also useless. We need a better one—namely, one that we don’t have to pick apart, that self-evidently shows us the way to success.

However, the problem has still not been solved. We are still working with a frozen bundle of badly-synchronized muscles that are now jammed together, and hurting. What can we do?

The first step, in my opinion, is to establish a new definition of flexibility. In order to begin that process, I share a quote by Drs. Ivo Waerlop and Shawn Allen, better known as The Gait Guys:

“Develop anterior strength to earn posterior length.”

This quote refers to the “anterior” (frontal) and “posterior” (rear) muscles of the body. The body is set up so that when the posterior muscles pull, the body stretches out. We can stand largely thanks to the posterior muscles. But that also means that they have a mechanical advantage over the anterior muscles: the posterior muscles are attached to the bones so that they can “beat” the anterior muscles.

Without going into too much detail—that is material for another post—the posterior advantage over anterior muscles is usually why we have tight hamstrings but weak hip flexors. Because the hamstrings “win,” they become tight, and because the flexors “lose,” they become weak.

Losses of flexibility typically work in this way. So, if we develop our anterior muscles, they will be capable of opposing themselve to our posterior muscles, and we will gain “posterior length”—essentially meaning more flexibility. What did we do? We increased the muscles’ “complementarity,” (their ability to oppose each other efficiently), and their “dynamism” (we brought the necessary muscles to a new level of mobility).

Therefore, we can propose a new definition of flexibility, that encompasses the typical, at-face-value definition of “increased ROM,” and also outlines a useful path for the athlete to take.

I define “flexibility” as the increased complementarity and dynamism of a relevant set of opposing muscles.

This definition encompasses the previous definition because increased complementarity and dynamism imply that the muscles are able to move the joint in increasingly wider arcs.

None of this should be taken to mean that stretching to unfreeze a completely frozen joint is a bad thing. The joint must be able to move in order to begin the process of synchronizing the muscles around it. But there are less invasive, and wiser ways of doing that, such as dynamic stretching (which has been found to have no beneficial effects for endurance runners anyway). But that alone doesn’t constitute a long-term solution.

The muscles should be trained to develop explosive, powerful complementarity and dynamism between themselves. The goal is that beyond a certain level of cultivation, dynamic stretching is no longer needed, and simply performing the function that the muscles have been taught to express becomes enough for the joint—or the system—to remain flexible throughout an entire athletic career.