Fascial NeuroBiology: An explanation for possible manual therapy treatment effects
Below is a guest post from Chris Beardsley in response to a recent post of mine that questioned the possibility of any manual intervention (this includes foam rolling) influencing the physical properties of fascia. It is also questioned how relevant is to pain and dysfunction.
Research Review: An analysis of Robert Scheip's paper on Fascial Plasticity
By: Chris Beardsley
more from Chris at his website: http://www.strengthandconditioningresearch.com/
Recently, Greg wrote about the problem of understanding if and how manual therapists modify fascia during their work. At the end of his post, he asked several very pertinent questions, two of which were: “by what means can your hands actually mold, shape or cause some change in fascia?” and “why can’t they do this in muscle, which is the far more responsive tissue to stress?”
In 2003, Robert Schleip wrote a substantial review article on fascia, in which he detailed how the nervous system might be involved in the process of manual therapy, the main points of which are summarized below. At the end, we can also see to what extent Schleip’s proposals shed light on Greg’s key questions.
The study: Fascial plasticity – a new neurobiological explanation: part 1, by Schleip, in Journal of Bodywork and Movement Therapies, 2003
Introducing fascia and manual therapy
Fascia surrounds every muscle and even each myofibril within the muscles, as well as wrapping around each internal organ of the body as visceral fascia. It is arranged in sheets that slide over the top of each other and also forms interconnecting lines that join various muscles together.
As part of their work, manual therapists seek to alter the qualities of the fascia in respect of the way it responds to tension or pressure. They do this in order to bring about reductions in pain or improvements in movement quality. How these changes and improvements occur is not certain.
In this review article, the Robert Schleip explains that fascia has a neural component as well as a mechanical component. Schleip proposes that it is this neural component that will help us understand what is happening during manual therapy. But first, he considers some early theories of what manual therapists are doing.
The classical model
Schleip explains that many of the current manual therapies stem from the practices of Rolf in the 1970s. Rolf applied considerable manual pressure to fascia with the express purpose of changing its density and arrangement. She proposed that the density of fascia could be altered to make it less dense and therefore more fluid.
This process of making a substance more fluid through mechanical pressure, technically called thixotropy, was later found by researchers to occur following long-term studies on fascia. However, Schleip notes that these thixotropic changes were found to reverse following removal of the pressure, which is not what Rolf was referring to, as manual therapy appears to involve sudden releases of tension as the result of fascial rearrangement under the hands and not slow, gradual alterations.
The piezoelectric model
Schleip explains that another proposal for the mechanism by which fascial plasticity could be explained is piezoelectricity. He notes that fascia researchers have proposed that fibroblasts and fibroclasts, which create and digest collagen fibers, might be responsive to the electric charges that are created through pressure. Many researchers are already aware of similar responses in bone. However, such changes again appear to occur over long periods of time, which is not the mechanism that manual therapists were looking for.
The need for a more rapid self-regulatory system
Because these two basic models cannot be used to explain the phenomenon of release that manual therapists observe in practice, Schleip therefore suggests that the nervous system must be included in any model of fascial plasticity.
Close but not quite: the Golgi reflex arc
Schleip explains that Golgi receptors are an important first step in understanding the neurophysiology of fascia. He explains that these receptors are found in all connective tissues, where they are called Golgi end organs in ligaments and Golgi tendon organs (GTOs) at the junction between muscle and tendon. Importantly, they are arranged in series with fascial fibers (unlike muscle spindles, which are arranged in parallel).
In a stretch, GTOs provide afferent feedback to the spinal cord, which causes the motor neurons to lower their firing rate and therefore reduce the tension produced by the muscle fibers. Schleip explains that researchers originally suggested that manual therapy might lead to a stimulation of GTOs, which could then result in a lower firing rate of certain motor neurons and consequently a reduction in the tension in the muscles. However, later research showed that the passive stretching of a muscle does not in fact stimulate the GTOs. This is because GTOs require active muscular tension to be stimulated because in a passive stretch the elasticity of the muscle absorbs the majority of the deformation, while in an active contraction, it is the tendon that elongates.
However, despite this setback, Schleip notes that this may well still be the right track to follow, as there are many other Golgi receptors in various places. It is possible that these less-well understood Golgi receptors could be the ones that are stimulated by manual therapists.
Ruffini and Pacini corpuscles
Schleip explains that researchers have found that the thoracolumbar fascia contains many mechanoreceptors. These mechanoreceptors take the form of three types: (1) large Pacini corpuscles and slightly smaller Paciniform corpuscles, (2) smaller and more longitudinal Ruffini organ, and (3) interstitial muscle receptors.
Schleip comments that the Pacini and Paciniform corpuscles respond to rapid changes in pressure but not to unchanging levels of high pressure. On the other hand, the Ruffini organs appear to respond in the opposite way. Schleip therefore suggests that it is possible that manual therapists may be stimulating Ruffini endings, which may then cause the nervous system to reduce the tension in some of the motor units within the muscle. (Greg's note: Ruffinis respond to gentle lateral skin stretch - you don't need to dig in deep to activate these receptors)
Schleip comments that only 20% of all the sensory nerves in the body belong to type I and II afferents. These are the ones that are activated by the muscle spindles, Golgi organs, Pacini corpuscles and Ruffini endings. On the other hand, he explains that 80% are type III and IV afferents and these have their origin in interstitial muscle receptors. In fact, Schleip explains that many of these receptors are actually within the fascia rather than inside the muscle and many of them are mechanoreceptors, with two main groups: low-threshold pressure units and high-threshold units. These mechanoreceptors could therefore be the ones responsible for the changes induced by manual therapy.
Motor units not muscles
Schleip reminds us that the central nervous system does not activate single muscles but rather activates groups of motor units. This is an important fact and it may help to explain the release of parts of tissue rather than whole muscles. Exactly what occurs in order for the tissue to release is unclear. Schleip suggests that it is possible that the release might be because of the lowered firing rate of a few motor units.
So what are manual therapists really doing?
So after all of this analysis, are we any closer to understanding what manual therapist are actually doing when they carry out their work? Can we answer two of Greg’s key questions, which are “by what means can your hands actually mold, shape or cause some change in fascia?” and “why can’t they do this in muscle, which is the far more responsive tissue to stress?”
Well, as detailed above, we can see that Schleip proposes a model in which manual therapy or fascial manipulation involves stimulating intra-fascial mechanoreceptors, which then causes changes in the afferent input to the central nervous system, which in turn causes an reduction in the level of muscle activation of specific groups of motor units.
So the answer to Greg’s two questions in the Schleip model would be that the hands are stimulating specific mechanoreceptors in the fascia, that cause afferent feedback to the brain, which then signals the muscles to release. The effect does not occur in muscle in the same way because the receptors are of different kinds in each tissue.
Of course, there remains a great deal of work to be done to understand the limitations and benefits of this model but it certainly helps to address many of the issues that Greg raised with the idea of the fascia being physically altered.
Chris Beardsley is a co-founder of Strength and Conditioning Research, a monthly publication that summarizes the latest fitness research for strength and sports coaches, personal trainers, and athletes. The above study review was taken from his Background product, which is collection of over fifty reviews of the most comprehensive review articles and meta-analyses of the fundamental concepts underlying exercise science.
Greg's final note: My question regarding fascia versus muscle as a more responsive tissue to stress only asked about the mechanical properties of these two tissues. I purposefully left out any discussion of the nervous system which I put at the top of the heap for responsiveness. When you treat a patient or foam roll yourself and feel better it is the nervous system that you have influenced. It is unlikely that any changes in the mechanical properties of tissues have occurred. You aren't more flexible because you broke up some scar tissue. You may have influenced the viscoelastic properties of tissue (a short term change) but more dominantly you have convinced the nervous system to let you move farther, with greater ease or with greater strength. An excellent model to understand this is the long term changes that occur in neuromuscular system with stretching. Following a stretching regime you don't change the stiffness of the muscle and it is unlikely that you change the mechanical architecture of muscle. Rather, you change the stretch tolerance. Your nervous system lets you bend farther. A brief review of stretching science was reviewed previously.
Related questions to think about: If you foamroll do you think that you are changing "tissue quality"? If so, how are you changing quality and what exactly is tissue quality? Could any changes to "tissue quality" merely be the nervous systems response to your rolling rather than changes in the structure properties (e.g. ground substance, extracellular matrix, collagen etc).