We all move like chocolates. Or worms. But not frogs.

With Christmas fresh in mind, I have to point out that when you’re a nerd like me you can’t just enjoy chocolate, you have to relate everything back to movement principles.

I'm sure other brands are available, but it particularly struck me when opening my 500th Lindor chocolate in a row that the mechanism of the wrapper is a good representation of joint movement. Seriously! The wrapper is sealed on a helical angle which means when you pull the ends apart the chocolate opens with a spiral. Despite your hands moving apart in a straight line, the movement that allows this is rotation. This is exactly how all joints work. This means that the planes of motion we talk about and were taught all through formal education are imaginary. Nothing is truly sagittal or frontal plane when it relates to joint actions. They are useful terms to discuss movement observations, but they do not represent what takes place in reality.

Two-dimensional, straight-line movements are superimposed onto a three-dimensional surface meaning it’s ALL rotation. This can be hard to visualise but can be demonstrated with an elegant movement paradox. If you put your arm straight out in front of you with thumbs up, then move the arm to the side (horizontal abduction), then bring the arm up so it’s by the side of your head, (flexion/adduction), then bring the arm straight down in front to the start position (extension), you will notice that you have changed the orientation of the wrist and your thumb now points sideways. A 90-degree rotation was achieved by straight line movements of other joints.

So what does this mean for flexion, extension, adduction etc?

If they don’t exist, what is happening? There are two types of rotation: internal and external. Rotation towards the body, and rotation away. This is compression, and expansion. Inhalation, exhalation. The ribs rotate away from the body to expand, and towards the body to compress. This is fundamentally how EVERYTHINHG in the Universe moves. Compress in one region and expand at another. Humans may have put things together in a complicated pattern, but it is all just a unique combination of expansions and compressions.

Because the body is complicated, and joints don’t operate in isolation but part of an integrated system, you typically don’t see movements that are purely expansive or compressive. More likely you see both things at the same time to different degrees, and biasing towards one end of the spectrum more than the other. Flexion, abduction, and external rotation are all expressions of expansion – which is why the pigeon pose, and FABER tests often feel so nice. Extension, adduction, and internal rotation are all expressions of compression. When we walk and run, we must go through ER into IR and back to ER again. Expansion, compression, re-expansion; like a worm. IR and compression and are how we produce force and, crucially, how we put that force into the ground. ER and expansion is how we realise speed of movement resulting from that compression. Without a hard surface to IR into, we stay in more ER. Think how a frog is flexed, abducted and externally rotated compared to a human: extended, adducted, internally rotated.

What does all this mean?

Once you get accustomed to this reality, it actually simplifies the whole approach to movement. When you need more force you need to perform an IR measure. When we squat, we go from relative expansion, through compression in the middle, back to expansion again at the bottom. This is why on the way back up as we pass through the middle phase we slow down, we internally rotate, and we adduct. It’s all about putting force down into the ground. It also means that tests of flexion and adduction etc provide a more holistic picture. You either lose expansive or compressive capability and restoring space to the system alleviates this. This gives you more options for how to address movement limitations. Putting heels in your shoes to squat is an example of providing more space, and therefore allowing easier movement.

An analogy for the whole system is that your body moves the way a bagpipe creates sound. Compression from an initial state of expansion. If you have a small bagpipe, you don’t have a lot of space into which to compress. You might be able to get a note or two, but you won’t complete the whole melody. This explains why you see so many people who are clear on isolated tests of flexion through hip, knee, and ankle, but then go to squat and hit a wall or fall over. They can compress to the extent of individual notes, but their bagpipe runs out of space when you try to do it all once. This is also why many strongmen cannot perform full range chin ups. It’s not a strength deficit, or even of range of motion deficit. It is due to them starting from a state of compression that simply runs out before the end of the task.

As mentioned earlier, this premise can be tough to grasp initially simply because it doesn’t align with illusion of movement we see on a daily basis, and because it probably isn’t what we were taught. But, once it is grasped as an overall concept it makes movement assessments simpler, more accurate, more informative, and also provides greater clarity with interventions, and more options for how to deliver those interventions.