And, while it isn’t a book, Robert Sapolsky’s Human Behavioral Biology series is worth watching; the first video is a must-watch.
I love this video by Tom Purvis.
I also love this poster from Bahram Jam.
[The information from this post is highly borrowed from Eyal Lederman’s essay, The Fall of the Postural-Biomechanical-Structural Model.]
Structuralism is a basic belief that structural imbalances, asymmetries, and misalignments increase the abnormal mechanical stresses imposed on the musculoskeletal system. These imbalances, asymmetries, and misalignments are causes of pain problems and of “faulty” movement.
When I think of structuralism, I think of Coldplay.
Antistructuralism is position rejecting the tenets of structuralism. It is the belief that structuralism most likely invalid or false, but that it is restricting, dangerous, primitive, and offers no unique benefits. It suggests that structuralism is harmful to society and people, and that even if structuralism was true, it would be undesirable.¹
When I think of antistructuralism, I think of Sara Bareilles.
I find it strange that in a time when we’re encouraged to be ourselves and accept whatever imperfections we may have, we can’t accept the various asymmetries and imperfections of our movement system as variations of normal.
I think this way of thought occurs because of the common view of the human body as a machine.
This assumption is made because the body appears to be, well, mechanical. We have have a system of bones and joints that work as a lever system. We have muscles that act like motors to move these lever systems. I’ve referred these mechanical analogies throughout the blog.
However, this assumption is simplistic. While at first glance our bodies may seem to be machine-like, with further inspection it becomes quite obvious that our bodies weren’t designed by well-educated, modern engineers. Our neurons are threshold elements, our muscles depend on nervous system signals and on it’s actual length, our sensory receptors are confusing, AND we’re always working with outdated information.
We’re a biological mess. We’re so characteristically… human.
If our bodies were made by the best engineers of the day, perhaps they would contain the anatomical and functional “ideals” seen in various textbooks.
It may be more accurate to think of the body as a garden. Our bodies were tinkered by evolution, not designed by the best and brightest engineers.
However, it’s not inherently “bad” to view the body as a machine. The concepts discussed in the mechanics section serve as useful heuristics that simplifies the complexity of movement. The problem occurs, however, when we go to far with our heuristics and assume they ARE reality.
Instead, we should view our bodies as predominantly a garden and marginally as a machine. Our bodies are primarily biological in nature. And, a feature of biological things is adaptation to the challenges faced in the environment to better survive novel conditions.
Greg Nuckols states it simply:
“Basically, your body feeds all of its stress, whether physiological or psychological, into a generalized pool of “adaptive reserves” that your body can use to elicit the specific adaptations necessary to respond to the stressors and strengthen the body against them in case the same stressors presents themselves in the future.”
Our bodies adapt to the various stresses placed on it. This is essentially just the principle of specificity: the body specifically adapts to the imposed demands paced on it. If anatomy isn’t perfectly balanced, symmetrical, or aligned, the body will compensate. This is not a dirty word; it’s useful.
Thus, the body has a surplus capacity to tolerate the various asymmetries, imbalances, and misalignments and can function. The system is capable of tolerating and compensating for these factors within the available surplus.²
Redundancy is usually considered a problem because it assumes that the controller, some program in the brain, must ensure that all of the individual elements produce very specific outputs for movement production.
However, the fact that there are more elements needed for completing a task is not necessarily a problem. Instead, it may provide us with motor abundance, meaning there are many ways to solve the same motor task.¹
While both words mean “something extra,” they have different connotations. Redundancy means something extra that you do not need, while abundance means something extra we enjoy and find useful.¹
Framing redundancy as abundant allows us to instead view a task as a challenge that can be solved in an infinite number of ways. As the cliche goes, we have many ways to skin a cat.
Motor abundance suggests that when we learn to solve a motor task, we take advantage of the fact that we have a near infinite degrees of freedom.
Instead of coming up with unique or “correct” solutions for the redundant degrees of freedom, we use the redundancy for more stable performance outcomes of any given motor task.
This allows us to be adaptable. We often have to deal with perturbations (external changes in the environment), fatigue, physical obstacles in the way… or we may want to multitask. Thus, abundance instead of redundancy.
Motor variability occurs because there are always more elemental variables (muscles, joints, motor units, etc.) in the effector system, which creates the movement, then there are in the actual outcome of the movement. These elements are called degrees of freedom.
These degrees of freedom are also redundant.
We have redundant anatomical degrees of freedom. We have more muscles than needed to perform various actions, and these muscles can span multiple joints.¹
We have redundant kinematic degrees of freedom. An infinite combination of types, locations, directions, and quality of movements is present.¹
We have redundant neuromuscular degrees of freedom. There are multiple motor neurons synapsing on the same muscle as well as many instances of a single motor neuron synapsing multiple muscles.¹
It’s essentially impossible to count the number of degrees of freedom in the human body. This redundancy exists in every single biological object and mechanical concept previously discussed.
If you attempt the same exact task many times, it will never be done exactly the same way, even if you consistently reach the same end goal.
Nikolai Bernstein, the OG of movement science, first observed this in his famous blacksmith study. He found that the variability of where the tip of a hammer landed on its target was smaller than the variability of the trajectories of individual joints of the subjects’ arm holding the hammer every single time.
His study observed expert blacksmiths, showing that even the best trained specialist won’t find a “correct” movement solution for a given task.
This motor variability is common in all human movement. Several attempts at the same task always lead to somewhat different patterns of performance. Bernstein beautifully described this observation as “repetition without repetition,” referring to the fact that each repetition was unique even though the end goal was not.¹
“Biology is messy. Your body is not a simple machine that you can feed inputs and expect predictable outputs.
Now, you can have a general idea of what’ll happen. But 1+1 doesn’t always equal 2. Maybe it’ll be 2 most of the time, but sometimes it’ll be 5, and sometimes it’ll be -3. […] There are billions of reactions taking place in your body every moment, affecting what’ll happen at the systemic level, while dozens of inputs are simultaneously entering the system via your thoughts and your senses (which then affect and modify other thoughts and sensations). 1+1 won’t always equal 2, because your body isn’t dealing with 1+1. It’s dealing with 1+1 plus a million other inputs and moderating factors. The result may be between 1.5 and 2.5 most of the time but there’s plenty of built in ambiguity that’s difficult to predict, harder to account for, and impossible to quantify.
Biology is nonlinear. You cannot control it. You can, at best, influence it.”
– Greg Nuckols
Notes of this section highly based on Neuroscience Online: An Electronic Textbook for the Neurosciences, Fundamentals of Motor Control, Explain Pain Supercharged, Pain: A Textbook for Health Professionals, Scott Haldeman’s Presidential Address and Human Motor Control.