Biological Learning and Control: Thoughts on Motor Control and its Applications to Movement
I recently finished the textbook, “Biological Learning and Control: How the Brain Builds Representations, Predicts Events, and Makes Decisions,” by Reza Shadmehr and Sandro Mussa-Ivaldi. It was a fascinating, but dense, exploration of how the brain interprets the signals from the environment and makes movement decisions. Though I skimmed most of the mathematical equations, the explanations behind the theories and its application to movement was more than interesting. I highlighted some of my favorite concepts, with thoughts on their relevancy to a movement setting.
“Prediction is due to internal models that describe what should happen. Measurements are due to reports from a sensory system that describes what actually did happen. Perception is a combination of the two, describing our belief about what happened.”
The authors make this statement on page one, in the introduction, as they lay out the fundamentals of human movement and motor control. When you are working in a predictable environment, this particular model is dependable, with perception accurately representing your prediction and your measurement reflecting what you expected to happen.
An example of this is squatting down to pick up a 15 pound kettlebell. If you have worked with kettlebells for a while, you can predict what the kettlebell is going to feel like and how much effort it will take to lift the kettlebell from the floor based on your previous experience using the same lifting strategy. If the kettlebell leaves the floor in the way you expected, you can measure whether your prediction about how it would feel and whether you would be successful was accurate. Your perception will be informed by what happened versus what you expected to happen. This hypothetical example is pretty cut and dry. Kettlebells are a familiar tool, the surface you are standing on is likely hard and consistent, and you have previous experience to draw upon, informing your movement pattern as you lift the kettlebell.
Let’s look instead at a commonly issued cue that is less easy to interpret. Let’s pretend you are told to stand up tall. What happens then?
Your prediction of how to perform the task is based on what you think it means to stand up tall, either because of pictures you have seen or previous instruction you have received. You will change your position to conform to what you believe is right. You will receive feedback from your sensory system that you have, indeed, changed your position. Your perception will reflect what you believe to be a position of standing up tall, but are you actually standing up tall, or are you arching your back, or sticking your chin out or throwing your ribs out? How are you accomplishing the task and is your internal representation (i.e., perception) of how you accomplish the task accurate?“Biomechanics are indeed important, but consider the fact that our movements change from the teenage years to young adulthood, and they continue to change as we grow older. Our movements change because of maladies such as Parkinson’s disease, schizophrenia, and depression.”
Is there a perfect form, a perfect way to squat, hinge, get down on the floor, or get out of bed? If our movements are a reflection of our thoughts, our emotional state, and our maturity, should we try to make an 8 year old swing a baseball bat like a 30 year old? Should we assume the clinically depressed war veteran should squat with the same form as a 25 year old ballet dancer? Are the movement ideals we insist upon in the weight room or the yoga room appropriate for every person? Or should there be more room for exploration and individual expression within a set of constraints? Maybe constraints can provide the framework for which a person can be given permission to explore? I realize I provided no answers, but I do think these questions are worth asking. “Properties of our muscles change due to a variety of disturbances, such as fatigue, disease, exercise, and development…Therefore, when the nervous system observes an error in performance, it faces a credit assignment problem…That is, adaptation to things that are likely to be permanent (fast states) should be remembered, while adaptation in response to things that appear transient (fast states) should be forgotten.”
If properties of our muscles change for a variety of reasons, it stands to reason our experience of our muscles working will also change. Two examples I see regularly are the sensation of joint cracking and the random zinger.
Clients will occasionally experience the sensation of joints cracking. The noise may not be audible to me, but it is audible to them. When they are asked to load the area differently, usually through a series of low grade isometrics, the sensation almost always goes away. Why? I don’t actually know, but maybe it has something to do with the nervous system detecting a change in performance, creating the feeling of stability. Regardless of the mechanism, what’s important is the client realizes the feeling they were experiencing is transient, a temporary blip that can be experienced differently with a novel input.
The random zinger occurs when someone moves a specific way and gets shooting nerve discomfort down the extremity. When someone has chronic pain and/or has not exercised in many years, the random zinger happens with new movements. In my experience, it resolves 99% of the time through approaching the same movement a different way, or simply doing something else for a little while before coming back to the same movement. Determining whether movements are potentially harmful is one of the jobs of the nervous system; every time you try a new movement, the nervous system has to make sure the movement is safe and worth repeating. If you don’t have very many movements in your movement toolbox because of inactivity, new movements pose an interesting problem. Your ability to predict what should happen is based on fewer past experiences, which affects how you perceive (and execute) the movement. Trying the movement again and not having any discomfort creates an opportunity for the movement task to be successful, making the painful response to the movement task temporary.“Suppose that the objective of any movement is to place our body in a state that is more rewarding…we get a natural balance between effortful behavior and maximizing reward: the movement that we perform is one that maximizes reward while minimizing effort.”
Why is so much of our brain devoted to movement? It could be argued we evolved to move so we could survive; survival is predicated on a number of factors; all of which involve some form of a reward, whether it’s food, water, sex, or not getting eaten by the predator. When you think about moving as a way to move to a place that is more rewarding, the relationship to movement changes.
It also creates an interesting disconnect between the current prescriptive view of exercise and the authors’ theory that movement should maximize reward while minimizing effort. “Do 8-10 exercises, 1-3 sets, of every major muscle group at least two times per week, for muscle health.” It’s no wonder adherence to weight lifting is low—nothing about the current exercise prescription appeals to a sense of reward (and curiously, drop out rates in exercise programs among people with depression is often high, despite the fact exercise tends to improve depression symptoms).
Perhaps this is why people are being drawn to movements modalities that invoke a sense of flow—there is something inherently rewarding about trying to get from point a to point b to point c in an interesting way. In today’s world, building strength is necessary (we are missing the foundational strength that was required hundreds of years ago just to get through the day), but we also seem to have forgotten that movement can be rewarding and that building efficiency through coordination makes the experience more pleasurable. This could also be an argument for more task based movement—figuring out how to lunge down to pick up a series of objects or picking up a heavy object and moving it across the room, setting it down somewhere else are meaningful objectives with a measurable outcome. You are designed to figure out how to maximize reward (successful completion), while minimizing effort. Tissues will adapt and get stronger, more motor units will be recruited with subsequent attempts, and you will become more capable with meaningful practice.
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