Jared Powell:
Keep your shoulder blade back and down. Don't shrug, retract your scapula. Maintain neutral posture. Move exactly like this. Now, if you've ever been to a physio for a shoulder problem, or if you're a musculoskeletal clinician giving these cues, you've heard or given some version of that list. And underpinning every single one of those cues is an assumption about human movement. The assumption is as follows, there is one singular correct way to move.
Jared Powell:
And if someone's movement looks different from the correct pattern, that difference is the problem. Today, I want to prosecute this very idea because this assumption misunderstands something fundamental about how our nervous system is built. And curiously, the person who worked this out did it in the 1930s, nearly 100 years ago, watching Blacksmith's swing hammers. By the end of this episode, I want you to walk away with a different question to ask or to mull over. Not is this movement correct, but something that I think is much more useful and indeed much more accurate. I'm Dr. Jared Powell. I'm a physio and researcher and I run shoulder physio education. This podcast exists in some form to hunt zombie ideas. The ones that get killed off in the literature, buried, disproven, and somehow keep roaming around clinics anyway, because nobody told them they're dead. In this episode's zombie hunt, we go after the notion of there being one correct movement.
Jared Powell:
Let's rip in. Okay, so before we get to the blacksmiths, I think it's worth asking where did the one correct pattern idea come from in musculoskeletal rehabilitation? Now, a lot of it traces back to work from the late 1980s and early 1990s. Punjabi's model of spinal stability and Bergmark's biomechanical work separating the deep local stabilizing muscles from the more superficial global movers. Reasonable models built from cadaveric and engineering data, but clinically they got translated into something more rigid. The idea that there's a specific correct pattern of deep muscle recruitment. Think transversus abdominis, multifidus, et cetera, et cetera. And that people in pain have lost this correct pattern of muscle recruitment. And then the, the solution becomes retrain the pattern, restore the stability and fix the pain. This is where core stability comes from. Matthew Lowe, writing in the Journal of Orthopedic and Sports Physical Therapy in 2018 points out that core stability doesn't even have a clear linguistic relationship to movement.
Jared Powell:
It's a vague surrogate term standing in for a much more complicated concept that of motor control that the field still hasn't agreed on a definition for. Lowe also cites research showing that language like instability, poor motor control and incorrect movement pattern measurably increases fear avoidance and guarding behavior in patients. Telling someone their spine or their shoulder or whatever joint you want to think of is unstable and needs correcting changes how they move, how much they're willing to move and how threatened they fel whilst doing it. So that's the paradigm that we're up against. One correct movement, deviation equals dysfunction, correction equals treatment. Where did it go so wrong? Let's go back a little bit further than Panjabi, all the way to a Russian physiologist and a workshop full of blacksmiths. Now, Nikolai Bernstein was working in the Soviet Union in the 1930s and he was interested in skilled labor, specifically blacksmiths who were striking a chisel with a hammer thousands of times a day every single day for years and years and years.
Jared Powell:
Now, if the on correct pattern idea is right, you would expect a master blacksmith after decades upon decades of repetition to have essentially automated that movement. They, you would expect the same joint angles, maybe the same muscle activations, hammer strike after hammer strike, almost like a machine. But that's not what Bernstein found. What he found was that the path of the hammerhead, the actual outcome, the thing that matters, the thing that hits the chisel in the same spot with the same force rep after rep after rep was remarkably consistent. But the way that the blacksmith's body got the hammer to its desired location, the shoulder angle, the elbow angle, the wrist angle, how those joints coordinated moment to moment was actually highly variable. So from trial to trial, from swing to swing, the joints were doing something slightly different every single time, even though the hammer got seemingly to the correct location with each repetition.
Jared Powell:
Now, Bernstein gave this a name that's now one of the most quoted phrases in motor control research. Repetition without repetition. So the blacksmith repeats the task but never repeats the exact same execution to get there. Now, why is this surprising? Because the human body has vastly more mechanical degrees of freedom than any task strictly requires. Think about how many joints, how many muscles, how many combinations of the two are available just to swing a hammer or closer to home to reach overhead for a coffee mark or to do a bench press or to do a lap pull-up. Traditional thinking treated this as a problem that the brain had to solve. It's called the degrees of freedom problem. With this many possible solutions, how does the nervous system pick the right on? Bernstein's answer reframes the entire question. The nervous system isn't actually hunting for a correct solution out of a seemingly overwhelming set of options.
Jared Powell:
It's finding a workable solution and it's perfectly happy to find a different workable solution next time and the time after that as long as the outcome holds. That's the important part, the outcome. So I want you to hold that thought because I think it maps directly onto the shoulder. As you know, I'm gonna bring everything back to the shoulder and this podcast episode is no different. So reaching overhead can be solved with more or less scapula upward rotation, more or less thoracic extension, different combinations of humeral movement, and this isn't hypothetical. A famous study from Willmore & Smith in 2021 shows exactly this kind of variability in scapula movement across different loads, different speeds, comparing dominant versus non-dominant arms and between individuals. There seems to be no single normal scapula pattern in the literature. There never has been, and I don't think there ever will be.
Jared Powell:
So Bernstein gives us the observation that skilled movement is consistent in outcome. Remember that, consistent in outcome. But now here's the key point, variable in execution, consistent in outcome, variable in execution. What he doesn't fully give us is why that's a good thing rather than just an interesting quirk of human movement. For that, we need to jump forward about 70-odd years to a researcher named Mark Latash. Now, Latash's contribution is, I think, one of the more important reframes in all of motor control science and it comes down pithily to a single sentence. And it's actually baked into the title of his 2012 paper. Now, the paper is called The Bliss, Not the Problem of Motor Abundance, Not Redundancy. Listen to that title again and reflect on it slowly because I think each word is important. The bliss, not the problem of motor abundance, not redundancy.
Jared Powell:
Let me explain. For decades, the field called this the motor redundancy problem. Redundancy, like it's a design flaw, like having more ways to move than strictly necessary is something that the brain has to fight against, has to solve, has to eliminate down to one efficient answer. That's what motor redundancy was taken to me. Now, Latasha's argument is that this framing is completely backwards.
Jared Powell:
It's not a redundancy problem. It's a motor abundance. And abundance I don't think is something that should be eliminated and Mark Latash didn't think so either. It's the entire reason the system, our nervous system seems to work as well as it does. Here's the logic according to Latash. If you only had one way to reach overhead, what happens to the movement the moment something changes? For example, your shoulder is fatigued, you're carrying something in the other hand, you're reaching around an obstacle, you're in pain and you're guarding slightly. A system with only one solution breaks the instant the conditions change. A system with many available solutions can lose one option and still succeed because it has others in reserve. It has abundance. Latash also draws a distinction that I think is underused in clinical conversations about variability. The difference between good variability and bad variability.
Jared Powell:
Not all variability is noise that needs to be minimized and actually not all of it is meaningful adaptation. Some can be harmful. Some variability changes the outcome. That's not the good kind, that's the kind you'd want to reduce. But a large amount of variability present in skilled movement doesn't change the outcome at all. That's good variance. And Latash argues it's precisely what allows a skilled system to absorb a perturbation, a secondary task, a change in conditions without the performance falling apart. This builds a reserve. This builds a capacity. Now, I wanna give you one more piece of this briefly because it explains why this isn't just a clever reframing. It's grounded in real theory of how the nervous system might work. It comes from a physiologist named Anatol Feldman, and it's called the equilibrium points or referent configuration hypothesis. The idea is that the brain might not be calculating individual muscle forces and joint trajectories at all.
Jared Powell:
Instead, it specifies a goal state, a referent configuration, which is the goal state, and the actual movement emerges, emerges as the key word, from that complex interaction between the body, the muscles, and the environment settling toward that state. Now, Latash argues that this theory is exactly what you'd expect to find underlying a system built on abundance rather than one rigid pre-computed answer. Now, this is absolutely a rabbit hole for another day. Don't worry. We're not gona get further into it in today's episode, but it's worth knowing that it's there and it's not just a nice metaphor. There is a serious, robust and complicated mechanistic theory behind it. The line from Latash that I really love is as follows. A movement system should be judged by its ability to maintain function when conditions change, not by how perfectly it performs under on single condition. Say that sentence to yourself the next time you're tempted to assess someone purely on whether their movement looks textbook correct in a clinic under ideal, unloaded, unhurried conditions.
Jared Powell:
Thank you. Now, I need to heed off a misreading here or a potential misreading because it's an easy misreading to make. None of this means that more variability is always better. That's not what the evidence says and sloppy takes on this idea do harm in the other direction. Let me take you to Nicole Sturgie's 2011 review that lays out what's often called the inverted relationship between variability and health. Now picture a shape. Flip it upside down. On one end, you have too little variability. That's rigid, robotic, over-constrained movement. On the other end, you have too much variability. That's noisy, chaotic, erratic, and unpredictable movement. Neither end is where you wanna be. Neither end is where healthy function lives. It lives in the middle. It always lives in the middle. There's a mechanistic reason both extremes are a problem, not just a theoretical one.
Jared Powell:
Too little variability means the same tissue gets loaded the same way repeatedly without redistribution. Think of early specialization. The six-year-old who starts running day in, day out, day in, day out and doesn't develop their general physical capacity. That kid or any person who starts running without doing anything else is perhaps more at risk of developing an overuse injury to the lower limb. Too much variability on the other hand is associated with erratic unpredictable movement and a higher risk of acute injury because the system has lost the ability to reliably control the outcome at all. So maybe the goal was never maximize variability. It's adaptability, the capacity to move successfully between multiple workable solutions as conditions demand without losing the outcome, without sacrificing the goal. , One more layer of precision here. A 2022 scoping review by Cowan and colleagues looked at 43 sports science papers and found the term movement variability used 280 different ways, 60% of the time without any definition at all.
Jared Powell:
That's most of a field using the same word to mean genuinely different things. Their proposed fix is a three-way split and I think it's clarifying enough to borrow for our clinical language too. Strategic variability, the different approaches or strategies available to solve a task. Reaching overhead with more scapula upward rotation versus less, for example, that's number one. Number two is execution variability. The intentional and unintentional adjustments within a single strategy, trial to trial, repetition to repetition. This is literally Bernstein's blacksmith finding, repetition without repetition. And number three is outcome variability, whether the actual result changes. Did the reach succeed? Did the pain come back? Now you generally don't want outcome variability. That's inconsistent pain, inconsistent function, but you probably want healthy strategic and execution variability because that's exactly what makes the outcome stay consistent when conditions change. Low outcome variability built on a foundation of rich strategic and execution variability.
Jared Powell:
That's the profile of a resilient and adaptable system. Low outcome variability built on rigid strategy and execution, one pattern drill to precision is actually the profile perhaps paradoxically of a brittle one. Let's bring all this all the way back to the shoulder and to scapula dyskinesis specifically because this is where theory stops being abstract and starts being informative. Now we already touched on the Wilmore and Smith's finding that scapular movement varies enormously and normally from person to person with load, with speed, with limb dominance, and whether the task is bilateral or unilateral and just individual variation between people. There is no single normula scapular pattern to deviate from according to the latest evidence. But wait, there's more. They discussed studies where pain improved, function improved, and scapular kinematics barely changed at all. So one would think that if the mechanism of improvement was we restored normal scapular motion, we would expect to see the scapular motion change alongside the improvement.
Jared Powell:
Often we don't. In 2016, 10 years ago, McQuaid and colleagues wrote, "Scapular movement variability should be embraced as a central nervous system optimization strategy rather than as a pathological factor." A beautiful and elegant sentence. So we can take scapular movement variability, often pathologize the scapular dyskinesis as perhaps adaptive. And in a given person, in a given context, it's a perfectly workable solution. The shoulder is doing exactly what Bernstein's nervous system does. It's finding a solution, not the solution, given whatever constraints that shoulder is currently working under. So the question changes. It, it changes from not, is this a normal movement? And instead becomes what problem is this movement solving and what's currently constraining the options available to solve it? All right. So what does all this mumbo jumbo technical philosophical motor control stuff actually mean clinically? So it reframes assessment. So instead of hunting for the faulty movement to correct, ask what's constraining this person's available options?
Jared Powell:
Is pain constraining them? Is it fear? Is it reduced low tolerance? Is it low confidence? Is it genuine stiffness? Are there strength deficits? Is there poor sleep? Is there poor systemic health? Is there deconditioning? Vas and colleagues in a 2023 paper on affordance-based practice describe a case that's relevant here, a patient called Carla, 18 years into a complicated back pain journey where her, where her kinematics barely changed across treatment but her function and confidence were transformed once the actual constraints were addressed, fear, guarding, and a rigid belief there was one correct way to move that she was failing to achieve. They were her constraints, her movement didn't change and she got better once those constraints were addressed. It also reframes treatment. So in treatment, we should move to manipulating or influencing constraints. That means graded exposure, perhaps resistance training, sensible load management, deliberately building confidence and deliberately varying practice, not drilling one correct pattern over and over, but giving the shoulder or the spine or the knee multiple ways to move to solve the same task across sessions and conditions.
Jared Powell:
Reaching overhead, standing, reaching loaded, reaching fatigued, reaching under time pressure. These are all examples of varying practice to develop resilient movement. There's a paper from Phil Glasgow and colleagues that frames this idea elegantly. Is the capacity to adapt to variable stimuli the key driver of injury and illness prevention? Not the achievement of one ideal pattern, the capacity to adapt. And here's what that looks like in practice concretely. Stop cueing a single correct scapula position as the finish line of rehabilitation. Build variability into your exercise selection intentionally, deliberately. Same underlying goal, different constraints, different sessions. Treat dyskinesis as information about someone's constraints to their movement, not a diagnosis that needs correcting. And judge progress by capacity under changing conditions, load, fatigue, novel tasks, rather than by how closely someone's movement resembles some idealized picture in a textbook that nobody can actually achieve. If I had to compress the entire argument of this episode into one sentence, it will be this.
Jared Powell:
Rehabilitation isn't the restoration of a single ideal movement pattern. It's the expansion of a person's repertoire of successful movement solutions. Let's bring it all the way back around to the start of this episode. Bernstein watched blacksmiths and found that skilled movement is consistent in outcome but variable in execution. That's repetition without repetition. Latash then took that observation and reframed it entirely. It's not a redundancy problem to be solved. It's indeed a motor abundance and abundance is the source of resilience. It is not a design flaw. Nicole Sturgie showed us there's a healthy middle zone of movement variability. Adaptable, not rigid, not chaotic. And then Cowan's framework gives us the precision to say exactly what kind of variability we're talking about. Mcquaid and Wilmore showed that this is precisely what plays out in the shoulder and clinically all of it points in the same direction. Treat the constraints limiting someone's option, not the pattern itself.
Jared Powell:
We should embrace movement variability as long as the outcome is successful. We should look to finding a particular solution, not finding one idealized correct way to move. If you want to go further down this hole, this rabbit hole, Feldman's equilibrium point theory is a fascinating rabbit hole, but it will require some reading. Maybe that is a future episode. Anyway, enough of me for today. Thanks for listening to this episode of The Shoulder Physio Podcast. I'm Jared Powell. I'll chat to you soon. The Shoulder Physio Podcast would like to acknowledge that this episode was recorded from the lands of the Tirabalang people. I also acknowledge the traditional custodians of the lands on which each of you are living, learning, and working from every day. I pay my respects to elders past, present, and emerging and celebrate the diversity of Aboriginal and Torres Strait Islander peoples and their ongoing cultures and connections to the lands and waters of Australia.
Jared Powell:
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