ABR 2: Stress Shielding and the Vicious Cycle

As we begin to make the mental shift from force generation (muscles) to force transfer (connective tissue) as a target for therapeutic interventions, one of the first things we need to realize is that the body of a brain-injured person, or pa erson with CP, is a mix of strong and weak tissues, often in combinations that boggle the mind.

Traditionally, we have been obsessed with the strong, bullying tissues.  We give medications to relax them, do surgery to release them, inject Botox to paralyze them, but never really give a thought to the other side of the coin.  How do we strengthen the weak tissues?  I envision it at somewhat like the challenges in classrooms today.  Do we keep the class moving along together by holding back the bright children (easy) or strengthening the challenged learners (difficult)?

We've focused on the strong partially because we have had no means to strengthen the weak.  ABR gives us this opportunity, but it doesn't mean the strong tissues are going to give up without resistance.  In fact, they have become so adept at their roles, which in some cases are helpful to the person although ultimately destructive  (like the high muscle tone that may help a child sit,  but will eventually contort the spine), that we must sneak past them to build up the weak tissues.

This is a rough picture of something called "Stress Shielding", where the strong tissues absorb incoming mechanical stresses to protect the weaker tissues, and in the process become even  stronger while the weak tissues continue their decline fomented by neglect.

In a normal body, there is a cycle of tissue remodeling that looks like this, what Leonid has termed "The Virtuous (Sustainable) Cycle":

This cycle can continue in a positive, healthy way  because when mechanical stress enters the body it is sustainably and efficiently distribute by and between tissues that are balanced.  This well-distributed stress is then used to maintain the vitality of the tissues appropriately, so that the cycle can continue.

In a person whose tissue are a mix of strong and weak, the cycle looks like this:

I know the words on the outside of the circle are hard to read, but they are the lists of interventions that are typically applied to counteract the negatives at each of the stations of the circle.  Usually, they are of little to no avail in moderately to severely impacted people, and so their  movement through the vicious cycle continues.

You can jump in at any point on the circle and envision what happens.  Say that you start at "irregular muscle activation" -- this pattern of use leads to tissue remodeling that reinforces this negative pattern...reinforcing the underlying mix of strong and weak.  With the tissue differentiated this way, stress shielding kicks in, as the strong absorb the lion's share of mechanical stress, and deprive weak tissue of the stress they need to get stronger.  The disparities between the tissues lead to internal force imbalances,  with the strong tissues being strengthened even more by the imbalance.  This  leads us right back to irregular muscle activation.

Look, many physically disabled people have a very high "Motor IQ"...being so limited they are endlessly creative and persistent in finding a way, any way, to make their bodies accomplish what they desire.  If "irregular muscle activation" allows them to use a communication device or control a power chair, it's very difficult to say , "Hey, try not to use your body in that way -- it's a destructive pattern."

But, we are not just talking about voluntary muscles, we are talking about all tissues, so halting this destructive cycle is not about "retraining muscle movement".  It is ongoing 24/7, even as a person is apparently still, or even sleeping.  The only way to reverse it is by strengthening the weak tissue, to balance the force distribution and negate the stress shielding response.

A good visual analogy of stress shielding is to align a length of steel cable next to an equivalent length of rubber band.  As you stretch them together, you know that they will only reach the length of the steel cable, which will be absorbing all of the stress.  The only way to introduce stress to the rubber band is to work around (without) the cable.

How can we do this in the body?  Our first instinct, when trying to provide mechanical stress to deep fascia, is to press harder, to make sure the stress reaches far enough.  All we are doing with this approach is activating the stress shielding response and strengthening the strong.

We have to go gently in --- so gently that the movement is almost imperceptible. It truly is like sneaking in under a wire.  ABR aims for a 1-2% deformation of underlying tissue.  To compare, range of motion exercises and fascial release generally aim for 3-8% deformation.  Beside activation of stress shielding, there are a couple of other challenges with this higher range.

Tissue deformation at 3-8% is the introduction of microtrauma to the tissues.  This is how healthy people get stronger.  When we push ourselves at the gym, our muscles respond to the microtrauma by getting stronger over time.  But, recall that people in the moderate to severe range of impact are metabolically broke -- they can't afford to fix microtraumas, especially not on a daily basis  (as range of motion is often prescribed) and in many areas simultaneously.

Secondly,  to achieve gains from range of motion exercises, they must be applied to the very end of the range.  This gets rather technical and challenging, and is a skill difficult to easily and effectively transfer into the hands of parents and caregivers.

So, ABR provides a fortunate confluence of variables:  the 1-2% deformation of tissue sneaks past stress-shielding, doesn't induce physically-expensive microtrauma, and can be safely accomplished by lay people.  And yes, this small window also means that it takes time and repetition.  ABR is not a quick fix, not even a moderately-fast fix.  It is a long-term, one small step at a time approach.

But hey, our brain injured loved ones are never standing still...they are either getting better or worse each day.  So, I am more than happy to take small steps, as long as I know they are in the right direction.

I know this was a really long posting....now that I've given you the "why" of the ABR technique, tomorrow I will delve more deeply into the "how"