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Why We Don’t Elongate Fascia (pt. 2)

This post is the second of a two-part series investigating the ideas of fascial manipulation. In the first part, I discussed the biomechanical properties of plastic and elastic tissue deformation of connective tissue. These principles demonstrate that we are unlikely to elongate and change the shape of fascia with manual therapy despite numerous claims to the contrary. In this post I want to explore another biomechanical and physiological principle that casts further doubt on the idea of causing structure (length) change in those tissues through manual therapy.

Here is a simplified cross-sectional representation of the skin and underlying layers that are affected when force is applied to the soft tissues through manual therapy.

layers of skin
Figure 1 Simplified representation of skin and fascia layers

The idea behind numerous fascial manipulation techniques is that when applying pressure to the tissues, that force is transmitted below the skin to the fascial tissues which then elongate as a result of the force application. Let’s take a look at some critical components of force application to see how this might play out.

Some manual therapy techniques predominantly use force that is entirely perpendicular to the skin, and in those techniques, we can perceive the force as going straight down into the skin and transmitted to the underlying tissues. Examples of this approach would be shiatsu or non-moving trigger point therapy using static compression of a small contact surface such as the thumb or a pressure tool.

However, most manual therapy techniques don’t rely on static non-moving methods. The majority of soft-tissue manipulation techniques use some form of gliding (with or without lubricant) on the skin, with the intent of affecting underlying tissues. You can divide the biomechanical force moving along the surface into a parallel component and a perpendicular component (Figure 2). The combination of these component forces produces an angular pressure into the tissues below the level of the skin. It is this angular aimed force applied below the skin that is theorized to be manipulating and changing the shape of the fascia.

components of force
Figure 2 Components of force applied in manual therapy

In 2002 a group of Canadian researchers published a paper exploring the proposed biomechanics of chiropractic adjustments (Bereznick, Ross, & McGill, 2002). In this paper, they demonstrated that the interface between the skin and the underlying connective tissues is almost frictionless, meaning it is extremely slippery and there is virtually no friction between the adjacent tissues. This concept has significant ramifications for manual therapy approaches.

If angular force application to the skin manipulates and elongates the underlying fascial tissue, there has to be significant friction between these surfaces. The friction is essential so the force applied to the skin can be directly transmitted below the level of the skin to the fascial tissues (which would theoretically elongate in response to the applied force). However, since this interface between the skin and underlying tissue is virtually frictionless, very little of that parallel directed force component can be applied to the underlying tissues.

In part one of this two-part series I discussed how the amount of force required to cause a change in fascial shape would have to be very high because fascia is highly elastic. As a result, it would take a very high force load to produce a lasting (plastic) change in the tissue structure. This idea of the frictionless interface makes that force application even less likely because it appears that the skin is slipping over the underlying tissue to a high degree.

There could be an argument that fascia is getting pulled when the slack is taken up by the skin slipping over the underlying tissues. After all, it can only slip so far before the slack is taken up and the skin is pulling on underlying structures. However, if this is what is manipulating the fascia, then it means the tension (pulling) forces between the skin and underlying fascia are so strong that they can cause plastic (permanent) deformation of the fascia just by pulling the skin. However, this approach would also require force loads far beyond those applied in manual therapy.

Again, we know that many clients and practitioners report significant benefits of fascial therapy including pain reduction, greater freedom of movement, and enhanced sense of well-being. So it doesn’t mean that there aren’t great benefits to various ‘fascial manipulation’ methods. However, it is far more likely that those benefits are coming through other means such as neurophysiological responses as opposed to mechanically lengthening the fascia.

Bereznick, D. E., Ross, K., & McGill, S. M. (2002). The frictional properties at the thoracic skin-fascia interface: Implications in spine manipulation. Clinical Biomechanics, 17(4), 297–303. https://doi.org/10.1016/S0021-9290(02)00014-3

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