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Recovery Tip

Did you know that your core muscles, which are the deepest layer of your tummy muscles, should work at all times to brace and protect your back? These muscles switch off due to pain and it takes 50,000 repetitions before they work automatically again to protect your back!

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Friday
Nov272015

Mechanotransduction

 

Mechanotransduction - Why does physio work?

Physiotherapists have a lot of good knowledge that helps patients to recover from injury, manage disease and achieve their functional goals. But what is really going on when a physio puts their hands on a body? What changes are happening to make healing happen?

The complex answer is ‘mechanotransduction’. This fancy word describes the phenomenon when cells respond to mechanical loading (the forces that go through our bodies as we move, like compression, shear, tension, torsion and bending). 

 

So how does that work?

Mechanotransduction has three stages. Let’s use a construction analogy to help explain.

Imagine a construction site inside a studio apartment, within a block of flats. The room is divided into sections by wooden beams holding the roof up, and there is a worker standing in each section.

Tenants on the floor above start jumping on the roof, causing the roof to buckle a little and the wooden beams to wobble.

 

1)   Mechanocoupling

Our construction workers are worried their rooves might fall down, because there are people upstairs jumping around. The forces coming down on the worker’s section are stressing them out. They know something is happening, so they switch the light on in their section.

In this situation, our workers are like the cell nucleus or the ‘brain’ of each cell. The physical squishing of each cell alerts it that force is moving through it, which causes the cell to produce a signal (the light).

 

2)   Cell-to-cell communication

Each of our workers is worried about the other workers in the sections surrounding their own, so they lean between the beams and go ‘Hey! Switch your light on, let everyone else know something is going on.’ Suddenly, lights are going on all over the apartment, including upstairs!

The cells that have been under loading tell other cells that they’re under loading too, creating a tissue-wide response. These distant cells think they’ve been under load, even though they haven’t.

 

3)   Effector cell response

The light we’ve been talking about? It’s a light to let the workers know to start mixing concrete, creating building blocks and to start fortifying the walls of their individual sections. So it’s started! Wall fortification is going on all over the construction site. But don’t forget, the lights have gone on inside the adjacent apartments, the stairwell and the shop on the ground floor. Suddenly everyone is fortifying the walls throughout the building.

Cells create proteins. In this instance, the cell signal for mechanical loading creates the proteins that fortify cell walls and strengthen the matrix that the cells are living in so that they’re better able to distribute loading through the tissue with minimal damage or deformation.

An extra-cellular matrix is like the ‘extra’ parts of the building, the walls and floors that separate each apartment from each other (as opposed to the internal walls of each apartment which divide sections, cell walls). It means all the non-living pieces of a tissue (proteins) that come together to create structure for the living parts (the cells) to organise themselves into.

 

So are we always fortifying walls?

The answer to that is complicated too. The musculoskeletal system is like any other system in the body. It responds to what it’s being told by the brain, and the brain gives instructions based on what is happening inside and outside the body.

Additionally, there is always building and tearing down of structures in the body. But what matters is the ratio of construction to destruction.

If the structure, let’s say a bone, is getting a lot of cell signalling and protein production because it’s being loaded, there needs to be some breakdown of the matrix to keep it organised and make way for new matrix for the type of loading being experienced most.

 

Our construction workers are building their fortified walls, but we haven’t quite checked on their progress.

 

The type of loading we’re talking about in this analogy is compression. When the people upstairs are jumping around, they’re compressing the walls being built.

 

 

In this photo, a thigh bone (femur) has been chopped in half. You can see that towards the outer surface the bone is much thicker (labelled compact bone), allowing for more force to go through the bone before failing (breaking, fractures). The middle of the bone is more honeycomb-like, to keep the total weight of the bone down. 

In bones that don’t get a lot of loading, the walls aren’t very thick. This means that if there is a sudden loading (like when you fall over) they’re more likely to fracture, because they’re not very strong. However if you’re active, and your bones are more accustomed to that specific type of force, then the chances of the bone being damaged by that force is much less.

We can see these changes in other types of tissues too, for example tendons. In the top photo, the fibres are all collagen and flowing in the same direction. You can imagine taking each end and stretching them apart like a rubber band, to have them nice and springy.

 

In the photo below, the collagen fibres are disorganised and there are a lot of tendon cells in the mix (the purple dots). Imagine stretching this tendon out; it wouldn’t have a lot of give, would be brittle, and would probably snap pretty quickly. It’s not very good at its job.

 

 

 

Okay great. So what does that mean for physio?

Physiotherapy is useful to many people, for a variety of conditions. To cut a long story short, your physio has extensive training in how the human body works and in how the naturally occurring processes in the body can be manipulated, becoming advantageous for clients. When you visit a physiotherapist, they will prescribe a variety of self-care activities, exercises, postural corrections and other therapies to influence how your body maintains itself, to improve its function and reduce any pain that may be present.

In terms of mechanotransduction, physiotherapists are expertly equipped to help you gently load different structures in your body to build up the strength for load bearing without overwhelming those structures into becoming painful or failing. This is done in a way that is measured, safe and prevents complications for other structures in the body.