Clinical practice is often changed by research that sheds new light on treatment methods. When translating results from research studies to clinical practice we must not overgeneralize the results or use one single study as final unconfirmed proof of anything. However, there are times when a study is truly groundbreaking and is an indication of a major paradigm shift in our understanding of clinical effectiveness. I was recently introduced to a study that had been performed in the chiropractic field, but could have significant meaning for our work in massage therapy if these findings are confirmed.
The study in question was authored by Bereznick, Ross, & McGill and published in the journal, Clinical Biomechanics, in 2002.1 It is hard to believe this paper has been around for 15 years and has not garnered a lot more attention. The authors of the study were attempting to identify if a commonly held theoretical model of spinal adjustment in the chiropractic profession was biomechanically accurate. The results of what they found should be quite surprising to any soft-tissue therapist and really make us reconsider what happens in our work.
Friction is a key biomechanical concept that is essential for understanding this study’s application. Friction is the resistance one surface or object encounters when moving over another. We try to minimize uncomfortable friction of our hand sliding over our client’s skin by using lubricant during many massage techniques. Yet in other techniques we are trying to take advantage of friction between adjacent tissues for therapeutic purposes.
As mentioned earlier, the chief goal in this study was to identify if it was possible to apply forces to underlying tissues during spinal manipulation in the way many chiropractors are taught. In order for these techniques to work as they are proposed, there has to be significant friction between the skin and underlying tissues. In this study they devised a method for determining how much friction exists between the skin and underlying fascia. What they found is there is actually negligible friction between the skin and this underlying fascial tissue. That is easy to imagine if you have ever looked at the skin on a whole chicken before cooking it. Once you peel the skin back you notice the interface between the skin and underlying fascial tissue is very slippery.
The authors were looking at these biomechanical factors in relation to spinal manipulation, but the implications for massage and other soft-tissue treatments are seriously profound. If it is true that friction at the interface between the skin and fascia is negligible, then many models of soft-tissue therapy need to be modified.
In what are often described as “fascial techniques” there is an underlying assumption that we are applying a shear or tension force to tissues under the skin when we apply force with our hands to the skin. The idea is that shear force applied to the skin is transmitted below the skin’s layer into these other tissues. In order for this to actually occur, there has to be significant friction between the skin and underlying fascia so that you could get traction enough to pull on the underlying tissues without simply sliding the skin over the fascia and deeper tissues. However, this study showed that the interface between skin and fascia is essentially “traction-less” and if that is true, we can’t really pull on underlying tissues the way this has been described.
If this concept of a traction-less interface is accurate, here’s a few examples of various massage techniques that might need to be reconceptualized:
- Deep longitudinal stripping applications that are applied along the length of a muscle fiber with the intention of increasing muscle length. Many practitioners find this technique to be helpful in reducing hypertonicity in the muscle. However, if we are not actually pulling along the length of the muscle fiber, what is actually occurring? It could be that the primary benefits of this particular treatment are due to neurological responses to the pressure along the length of the muscle and not any mechanical force imparted to the muscle that is stretching or elongating tissue.
- The core concepts of many myofascial technique systems (myofascial release, structural integration, etc.) suggest that the fascial tissues are being pulled and stretched with the application of shear force techniques applied to the skin. If there is little to no traction between the skin and underlying fascia, you cannot impart these stretching forces to the underlying fascial tissues. Again, it seems more plausible that the beneficial effects from these treatment approaches could be neurological (from tensile stress on cutaneous nerves) and not related to mechanical pulling or stretching of underlying fascial tissues.
- Deep cross fiber applications (either sweeping cross fiber movements or more specific deep friction massage) have been advocated to help spread and broaden fibers to encourage their mobility. If you are unable to get significant traction between the skin and underlying tissues, it is uncertain how effective you could be in spreading or broadening individual fibers below. One thing that is somewhat different about these deep cross fiber applications is they are usually performed with direct compression (perpendicular to the skin) as opposed to a longitudinal gliding application. It is reasonable to wonder if direct compressive forces might be more effective in imparting mechanical force into the tissue then shear forces which would be dissipated through sliding of the superficial tissue over the underlying fascia. That will have to be explored with future research
These are just a few examples of various treatment techniques which may be operating in a completely different manner than what we thought. It does not mean that these techniques are no longer effective or that they don’t get beneficial results. It simply means what is occurring when we apply them may not be what we thought. It is actually important to understand what is actually occurring physiologically and biomechanically so we can help enhance the more positive aspects of these different treatment approaches. Hopefully, in the future we can see biomechanical research investigating these ideas more thoroughly to see if this traction-less interface is applicable throughout the body in the way this article suggests.
- Bereznick DE, Kim Ross J, McGill SM. The frictional properties at the thoracic skin-fascia interface: Implications in spine manipulation. Clin Biomech. 2002;17(4):297-303.