3d • 🤓 Nerds
Blog post #1
Why understanding movement requires more than muscles, joints and exercises
This one is for the Nerds.
I thought I’d challenge myself to write up a weekly blog post on Mondays for the nerds. Today is a ridiculously simple question:
How does the body work?
It’s a question I’ve become increasingly interested in throughout my career, and unfortunately, the more I learn, the less straightforward the answer seems to become.
Open an anatomy textbook and we can identify muscles, bones, joints, nerves, tendons, ligaments and organs.
Open a biomechanics textbook and we can start discussing forces, moments, levers, stiffness and load transfer.
Open a neuroscience textbook and suddenly we’re talking about sensory information, motor planning, cortical networks, reflexes, perception, learning and neuroplasticity.
Then we could study physiology.
Psychology.
Pain.
Fascia.
Motor learning.
Strength and conditioning.
Skill acquisition.
Behaviour.
The environment.
And somewhere amongst all of that…
a human being moves.
That is what makes movement so fascinating.
And it creates the central idea behind much of what we do:
The body doesn’t work in isolated parts, even though sometimes we need to study the parts to understand the whole.
The Problem With Breaking Humans Into Pieces
Reductionism has been extraordinarily useful for science.
If something is complicated, break it into smaller pieces.
Study the pieces.
Understand them.
Then reconstruct the system.
This approach has taught us an enormous amount about human anatomy and physiology.
We can identify the attachment sites of the gluteus medius.
We can measure quadriceps force.
We can examine tendon stiffness.
We can record muscle spindle activity.
We can study cortical activation during movement.
We can calculate joint moments during running.
All of that information matters.
But there is a potential problem.
Understanding every component individually doesn’t necessarily explain the behaviour of the whole system.
Think about music.
You could understand everything about the strings, timber, frets and acoustics of a guitar without understanding why Jimi Hendrix sounded different from the person playing guitar at your local pub.
Understanding the instrument matters.
But the instrument alone doesn’t explain the music.
Humans present us with a similar problem.
A knee is not functioning independently of the hip.
The hip isn’t independent of the trunk.
The musculoskeletal system isn’t independent of the nervous system.
The nervous system isn’t independent of sensory information.
And none of those systems operate independently of the environment in which the person is moving.
Researchers studying sports injury have increasingly recognised this problem. Bittencourt and colleagues, for example, proposed viewing injury as a complex emergent phenomenon, produced through interactions between a web of determinants rather than a single isolated “risk factor.” [1]
That doesn’t mean individual factors don’t matter.
It means their relationships matter too.
So What Actually Creates Movement?
A tempting model is:
Brain → Muscle → Joint → Movement
There’s some truth in that.
But it’s nowhere near the whole story.
A more useful starting point might be:
Brain ↔ Body ↔ Environment
All continuously exchanging information.
Consider something as simple as walking.
Your nervous system needs information about where your limbs are.
Your eyes provide information about the environment.
Your vestibular system contributes information about head movement and orientation.
Sensory receptors provide information relating to muscle length, tension, joint position, pressure and contact.
Previous experiences influence expectations.
The environment provides opportunities and constraints.
The nervous system continuously integrates information while the musculoskeletal system produces and manages force.
And movement itself generates new sensory information, which influences whatever happens next.
So rather than movement simply being an output, movement is also an input.
This is closely related to James Gibson’s ecological approach to perception.
Gibson argued that perception and action should not really be considered separate events.
We move because we perceive.
But importantly:
we also perceive because we move.
The environment therefore isn’t simply the background in which movement occurs.
It is part of the movement problem itself. [2]
Your Body Has to Know Where It Is
One particularly interesting piece of this puzzle is proprioception.
Close your eyes.
Hold your hand above your head.
You probably have a pretty reasonable idea where your hand is despite not being able to see it.
How?
The nervous system receives information from receptors throughout the body, including muscle spindles and Golgi tendon organs, alongside information from skin, joints and other tissues.
Proske and Gandevia describe proprioception as contributing to our sense of body position, movement and muscular force. [3]
This matters enormously.
Because movement requires more than simply producing force.
The nervous system needs information about the system producing it.
That creates an interesting loop:
Sensation → Movement → Sensation → Movement
And the loop never really stops.
Which is one reason I’ve become increasingly uncomfortable with thinking about movement purely through the lens of individual muscles.
The Body Has Options
Now things get even more interesting.
Imagine I ask ten people to pick a cup up from the floor.
Everyone successfully completes the task.
But if we measured every joint angle, muscle activation pattern, velocity and trajectory, none would perform it exactly the same way.
Even the same person wouldn’t reproduce precisely the same movement every time.
Nikolai Bernstein recognised this decades ago.
He famously described skilled practice as:
“repetition without repetition.”
The goal might remain consistent.
The solution doesn’t have to.
The human body possesses an enormous number of possible movement combinations, what Bernstein described through the problem of degrees of freedom.
Originally this abundance could appear to be a control problem.
How does the nervous system control so many possible moving parts?
But another interpretation has emerged:
Maybe all those options aren’t a problem.
Maybe they’re one of our greatest assets.
Modern work examining motor abundance, synergies and movement variability supports the idea that multiple movement solutions can allow the system to maintain performance while adapting to changing demands.
So variability isn’t necessarily noise.
Sometimes variability is adaptability.
Stability Might Not Mean “Don’t Move”
This changes how we can think about stability.
Traditionally, stability can easily become synonymous with stiffness:
Keep this still.
Brace harder.
Don’t let the knee move.
Don’t rotate.
Sometimes that’s exactly what we need.
But perhaps another useful definition is:
Stability is the ability to find an appropriate solution for the problem in front of you.
Standing on two feet on a flat gym floor requires one solution.
Landing from a rebound while another basketball player bumps you requires another.
Running along a predictable treadmill is different from running down a rocky trail.
A controlled Pilates exercise is different from returning a tennis serve.
The appropriate amount of stiffness, movement, force and variability changes according to the task.
So instead of asking:
“Is this movement stable?”
perhaps we should sometimes ask:
“Is this person stable enough for what they’re trying to do?”
The Environment Changes the Answer
This brings us back to Gibson.
Ecological psychology introduced the concept of affordances, roughly, the opportunities for action that emerge from the relationship between an individual and their environment. [2]
A 60 cm box means something very different to an elite high jumper than it does to an 85-year-old who has never trained.
The box hasn’t changed.
But the movement possibilities have.
This means movement isn’t determined solely by the environment.
And it isn’t determined solely by the body.
It emerges from the relationship between them.
That has enormous implications for training.
If someone only ever performs movements in predictable environments with precise instructions and no decision-making, we shouldn’t automatically assume those abilities will perfectly transfer into an unpredictable environment.
Research from Dustin Grooms and colleagues following ACL injury is particularly interesting here.
Their work suggests that ACL injury and reconstruction are not merely local mechanical events. Changes in sensorimotor and neural processing can accompany injury, and researchers have argued for incorporating visual, cognitive and motor-learning demands into rehabilitation rather than assessing physical capacity alone.
The knee matters.
The quadriceps matter.
Strength matters.
But the person using the knee matters too.
But Don’t Throw Biomechanics Away
At this point there’s a danger of swinging too far.
If movement is complex…
If pain is multifactorial…
If the brain matters…
If the environment matters…
Then perhaps biomechanics doesn’t matter?
Absolutely not.
Forces are real.
Gravity hasn’t stopped existing because we discovered neuroscience.
Tendons still experience load.
Muscles still produce force.
Joints still have anatomical constraints.
Tissues still possess finite capacities.
Training still produces mechanical stress.
The work of Jill Cook, Ebonie Rio and colleagues on tendinopathy demonstrates beautifully why tissue structure, function, pain and loading all deserve consideration without assuming that any one variable completely explains the clinical presentation.
Similarly, tendon research demonstrates that connective tissues adapt to their mechanical environment through mechanotransduction. Loading influences cellular signalling, collagen synthesis and tissue properties.
Biomechanics therefore matters enormously.
It just isn’t the only lens available.
The Body Transfers Load
And this brings us to another recurring theme in my own thinking:
Movement is fundamentally about managing and transferring force.
When you walk, run, throw, jump or lift something, force needs to travel through the system.
Different tissues contribute in different ways.
Muscles produce active force.
Tendons can store and return elastic energy.
Ligaments constrain motion.
Bones tolerate compression, bending and torsion.
Connective tissues contribute to force transmission.
The nervous system regulates muscular output.
Consider the pelvis.
Vleeming and colleagues’ work on the sacroiliac joint describes the pelvis not simply as several bones connected together, but as an important region for transferring load between the spine and lower limbs. Concepts such as form closure and force closure attempt to explain how anatomy, friction, ligamentous structures and muscular forces contribute to stability and load transfer.
Again:
It isn’t one muscle doing the job.
It is a system coordinating around a task.
What About Fascia?
This is where another fascinating rabbit hole begins.
Historically fascia was often treated as little more than packing material, the stuff you moved through during dissection to reach the “important” anatomy.
That view has changed substantially.
Fascial tissues are increasingly investigated for their mechanical, sensory and connective roles.
Researchers including Robert Schleip, Carla Stecco, Peter Huijing, Helene Langevin and others have contributed to a much richer understanding of connective tissue anatomy and physiology.
However, this is also an area where it’s easy to run much faster than the evidence.
Claims about fascial “lines”, emotional storage, releasing fascia or correcting entire kinetic chains can quickly move from interesting hypothesis to unjustified certainty.
So I think the useful position is somewhere in the middle:
Fascia matters.
It has mechanical properties.
It contains sensory innervation.
It participates in force transmission.
Its interfaces and extracellular matrix matter.
But fascia is another part of the system.
It isn’t the system.
Pain Complicates Everything Further
Now imagine the person we’re assessing is in pain.
Pain introduces another layer entirely.
One of the most important developments in modern pain science has been recognising that pain and tissue damage are related, but they are not identical phenomena.
David Butler, Lorimer Moseley, Ronald Melzack and many others have helped move pain science away from a simplistic:
Damage → pain model.
Pain involves nociceptive information, but its experience can also be influenced by context, previous experience, expectation, perceived threat, sensory processing and many other biological and psychosocial variables.
That doesn’t mean:
“Pain is all in your head.”
And it certainly doesn’t mean tissue doesn’t matter.
A ruptured Achilles is still a ruptured Achilles.
A fracture is still a fracture.
A highly irritable tendon still needs appropriate loading.
Rather, it means pain is another example of why biological systems resist simple explanations.
Sometimes structure matters enormously.
Sometimes sensitivity matters enormously.
Usually we need to understand both.
Capacity Matters
This is where rehabilitation and strength and conditioning start meeting each other.
Ultimately the person has to tolerate whatever their life demands.
Let’s say someone can currently tolerate 5 km of running.
Their weekend demands 8 km.
There’s a mismatch.
Or perhaps someone can produce excellent force during a controlled bilateral squat but struggles when asked to decelerate, rotate and make a decision during sport.
Again, there’s a mismatch.
I find it useful to separate two ideas:
Capability:
Can you perform the task?
Capacity:
How much of that task can you tolerate?
Someone may be capable of jumping once.
That doesn’t mean they’re prepared for 70 jumping and landing events during a basketball game.
This is why workload matters.
Windt and Gabbett’s work highlights the dynamic relationship between exposure, fatigue, fitness and injury risk. Training itself can simultaneously expose an athlete to risk while also creating the adaptations that make them more resilient.
So the goal isn’t simply:
Avoid load.
The goal is:
Develop the capacity to tolerate the required load.
Rehabilitation Should Restore Options
This leads to one of the ideas that has become central to how I think about rehabilitation.
The goal isn’t necessarily to create one “perfect” movement.
It’s often to restore options.
Perhaps initially we deliberately constrain movement.
After surgery, injury or during a highly irritable presentation, predictable and controlled environments can be incredibly useful.
We isolate.
We slow things down.
We reduce degrees of freedom.
We build strength.
We develop tolerance.
We practise specific skills.
But eventually life becomes messy again.
Speed increases.
Load increases.
Fatigue appears.
The environment changes.
Someone bumps into you.
The ground isn’t flat.
You need to look somewhere else.
You have to make a decision.
You miss your footing.
You react.
So eventually rehabilitation has to ask:
Can this system adapt when the original plan doesn’t work?
That question sits very close to Bernstein’s concept of movement variability, Gibson’s perception-action coupling, modern motor-learning approaches and the neurocognitive rehabilitation work emerging from researchers such as Grooms.
And This Is Where Play Becomes Interesting
This might also explain why I’m increasingly interested in play.
Play introduces things traditional exercise often removes.
Uncertainty.
Curiosity.
Exploration.
Decision-making.
Failure.
Success.
Reaction.
Competition.
Creativity.
Variability.
Joy.
Someone throwing a ball against a wall and reacting to an unpredictable rebound is solving a continuously changing movement problem.
Someone balancing across rocks is doing the same.
So is a child playing tag.
None of this means we should replace structured strength training with games.
A heavy deadlift develops qualities that tag doesn’t.
A controlled calf raise can load the Achilles in ways free play may not.
Pilates can provide opportunities for controlled exploration, strength and awareness that chaotic games may not.
Again:
We don’t need one method to win.
We need to understand what problem we’re trying to solve.
So… How Does the Body Work?
After all of that, we still haven’t answered the original question.
And that’s kind of the point.
Maybe there isn’t one answer.
A biomechanist might describe movement through forces and moments.
A neuroscientist might describe sensory integration and motor output.
A physiologist might discuss energy systems and tissue adaptation.
A psychologist might discuss attention, motivation and behaviour.
A strength coach might discuss force, velocity and capacity.
A therapist might discuss pain, sensitivity, range of motion and function.
An ecological psychologist might study the relationship between the person, task and environment.
They’re looking at the same human from different windows.
The mistake might be assuming that the view from one window explains the entire building.
A Working Model: Brain ↔ Body ↔ Environment
So for now, this is the model I find most useful:
BRAIN ↔ BODY ↔ ENVIRONMENT
The body provides structure, tissues, forces and physical capacity.
The brain and nervous system perceive, integrate, learn, predict, regulate and coordinate.
The environment provides information, constraints, opportunities and problems to solve.
None operates independently.
Movement emerges from their interaction.
And movement changes all three.
Training changes tissue.
Experience changes the nervous system.
Movement changes how we perceive our environment.
The environment changes the movement solutions available to us.
It is a loop rather than a line.
R-L-R
This thinking eventually led me towards something I’ve been developing and playing with called R-L-R: Right → Left → Right.
I want to be very clear here:
R-L-R is a working framework, not an established scientific theory.
It is my attempt to organise ideas from anatomy, neuroscience, biomechanics, motor learning, ecological psychology, rehabilitation and coaching into something clinically useful.
Very broadly:
RIGHT — Explore
See the whole.
Observe.
Move.
Gather information.
Explore possibilities.
Understand the person, task and environment.
LEFT — Refine
Zoom in.
Measure.
Strengthen.
Load.
Practise.
Analyse.
Build specific qualities.
RIGHT — Integrate
Return those qualities to meaningful movement.
Increase variability.
Add environmental information.
Increase speed, load and complexity.
Allow the person to solve problems again.
Or, even more simply:
Explore → Refine → Integrate.
Whether the neuroscience ultimately supports every part of the Right-Left-Right metaphor is something I’m still exploring.
And that’s okay.
A framework should be allowed to evolve when better evidence appears.
Maps Before Routes
Perhaps the bigger principle is this:
Build the map before prescribing the route.
Before deciding someone needs stronger glutes…
Understand the problem.
Before deciding someone needs more mobility…
Understand the problem.
Before blaming fascia…
Understand the problem.
Before blaming posture…
Understand the problem.
Before deciding pain is purely structural…
Understand the problem.
Before deciding pain is purely neurological…
Understand the problem.
Ask:
Who is the person?
What are they trying to do?
What can they currently do?
What can’t they currently tolerate?
What information is their system receiving?
What tissues need greater capacity?
What movement options are available?
What happens when the environment changes?
Then decide which tool might help.
Sometimes that’s treatment.
Sometimes Pilates.
Sometimes heavy strength training.
Sometimes graded exposure.
Sometimes motor learning.
Sometimes rest.
Sometimes play.
And sometimes the correct decision is referring to someone who knows considerably more about that particular problem than you do.
So what do we think Nerds?
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