Sunday, November 11, 2007

Structure vs. Function - Part II

Let's examine the debate between structuralists and functionalists some more with the ubiquitous ankle sprain for example.

Treatment for such an injury until a few years ago focused mostly on reducing swelling, early weight bearing, .... - and yet the single most important risk factor to suffer from another ankle sprain is still a preceding ankle sprain. The same happens in low back pain (LBP). Your "risk" to suffer from another episode of LBP is greatly enhanced by an episode of LBP in the past.

How come?

Well - the sad truth is that you cannot guarantee joint stability with sheer muscle force - and that was - and unfortunately still is - the theory behind most training regimens. It went something like this: if a joint is injured the best way to provide stability in the future is to exercise the muscles surrounding the joint.

Along come journals like the Journal of Applied Physiology (and others) and show that this simply doesn't work: muscles are way too slow to provide stability.

If you jump on a platform that suddenly tilts under your foot it takes just 10 milliseconds for your ankle to get hurt.

On the other hand muscle takes at least 50 milliseconds to react in the most basic and "primitive" way - with a reflex action.

Let me spell it out for you: muscles contract after (!) the injury has taken place - often making it worse in the process.

Interestingly enough students are taught this in physiology classes - the contraction times I mean. Yet 99.99% fail to make the connection that muscle action isn't sufficient to provide stability.

Lateral thinking rules the day once again. ;-)

You mean to say that training doesn't help at all?

Of course not - but the focus has to be on the timing of the muscle action. Scientists call this the "feed-forward" approach.

Your brain (using the eyes) continually scans your surroundings and the ground in front of you. It then prepares motor patterns based on the visual impression of the surface you are going to step on. In short: your muscles contract way in advance so that they are prepared for the moment when your foot hits the floor. That's when you need the braking force your muscles provide.

It's the same when you try to catch something: your brain computes the path the object travels, factors in gravity (or not - as Alain Berthoz has shown with Space Shuttle Astronauts) - and adjusts your hand muscles so that they are ready to intercept the object. It's all about predicting future events - even when they are just a few milliseconds away.

As for LBP, the same feed-forward mechanism applies: your brain tries to prepare the body for, say - catching (heavy) things by contracting the muscles around your "core". This increases intra-abdominal pressure - thereby enhancing spinal stability and providing a stable "platform" as it where for the extremities. Once you suffer from an episode of LBP this mechanism is put out of action - from then on you use a different motor pattern to control your trunk which isn't up to the demands of everyday life. The deep muscle system of the back stops working and the more superficial muscles take over. They have to exert a lot more force though to keep the trunk rigid during heavy tasks - so they tend to tighten considerably.

On a side note: Rectus Abdominis (the famous "six-pack" muscle) doesn't do anything for increasing intra abdominal pressure. For me it's still the most useless muscle out there.

Only by re-establishing normal motor function - by training coordination and by re-establishing the feed-forward mechanism can you reduce the risk of suffering from another episode of LBP.

Modern rehabilitation has to focus on two things:

one - restoring normal joint play and range of movement (Motion is lotion and creates lots of feedback)


two - training the feed-forward mechanism so that the brain becomes better (and a bit faster) at predicting the future, proprioception and reacting faster.

For the first task you are welcome to think in purely structural terms - damaged ligaments, scar tissue formation and so on and so forth.
But for the second one - re-programming motor patterns you have to think like your brain. Sounds strange - I know.

But think about it: your brain has to prepare itself and the body it resides in for a lot of tasks and challenges each and every day. It does so by storing information about previous events (called memories) and building up a huge database about the properties of different objects and surfaces so that it is prepared for the things that lie ahead.

I will come back to this topic with a series about Alain Berthoz book "The Brains Sense of Movement".


How does this picture fit the topic?
Well - some of the same principles are at work here: most people - when the see a fibre optic lamp - just think "lamp".

Me - I see a thousand possibilities. I see movement that can be captured over a period of a few seconds - creating very interesting patterns.

This is what purely structural thinking has lost: it only looks at static structures, snapshots of tissues in different stages (of healing).

Functionalists see change over time, function in a bigger context - and above all a brain that tries to make sense of an outside world and a virtual reality simulation of that world on the inside.

1 comment:

helium said...

> On a side note: Rectus Abdominis (the famous "six-pack" muscle) doesn't do anything for increasing intra abdominal pressure. For me it's still the most useless muscle out there.

I thought it is used for breaking in rotational movement. If you perform a golf swing you dont want to rotate around and around but the rotation has to stop prety uickly after you hit the ball. The RA helps with that.