Does Fascia Stretch?
In order to properly answer the question, “Does fascia stretch?”, it is important to establish at the outset what definitions to use. There are presently two definitions of the word fascia that have been submitted for acceptance to the Federative International Programme on Anatomical Terminologies (FIPAT): (1) “A fascia is a sheath, a sheet, or any other dissectible aggregations of connective tissue that forms beneath the skin to attach, enclose, and separate muscles and other internal organs”, and (2) “The fascial system consists of the three-dimensional continuum of soft, collagen containing, loose and dense fibrous connective tissues that permeate the body. It incorporates elements such as adipose tissue, adventitiae and neurovascular sheaths, aponeuroses, deep and superficial fasciae, epineurium, joint capsules, ligaments, membranes, meninges, myofascial expansions, periostea, retinacula, septa, tendons, visceral fasciae, and all the intramuscular and intermuscular connective tissues including endo-/peri-/epimysium. The fascial system interpenetrates and surrounds all organs, muscles, bones, and nerve fibers, endowing the body with a functional structure, and providing an environment that enables all body systems to operate in an integrated manner”. (1)
If we use the first, tissue-specific definition of fascia for the moment, then we would be obligated to restrict ourselves to considering only the kind of research designed to study the effects of mechanical stress and strain of connective tissue. Let’s start with the beginning of a two-part article in 2003 that may well have initiated a long-standing debate about whether fascia has the ability to stretch that still reverberates today. (2) In it, the author Schleip states at the outset, “…studies have shown that either much stronger forces or longer durations would be required for a permanent viscoelastic deformation of fascia”.
From this, the author determined that the thixotrophic (AKA “gel to sol”) model of connective tissue plasticity could no longer suffice as a valid explanation as to what occurs when either or both practitioner and client feel what many described as “a release”. That is, the colloid part of fascia—in the extracellular matrix, or ECM—does not in fact become more fluid during commonly applied short phases of manual therapy technique. Piezoelectricity was another model that tried to explain that therapeutic “release” was due to applied manual therapy pressure that created an electric charge that then stimulated fibroblasts to produce more collagen. When placed under the scrutiny of research, both models failed to adequately explain or otherwise account for short-term tissue change that practitioners claimed to feel and observe. Some writers of popular blogs and articles took this to mean that the evidence has shown that all fascia cannot be stretched: “Manual therapists need not feel threatened by the news that we cannot stretch fascia”. (3)
This new perspective—that fascia cannot be stretched, seemed to be further supported with a notable study in 2008,(4) with Schleip listed as an author along with Chaudry and others. The authors commented in that article that they came across other studies where some research authors reported evidence that supported practitioners’ observations and explanations of a tissue “release” while finding other studies that argued against it. Therefore, Schleip et al. stated that they undertook their own study to resolve a fundamental question underlying such diverse findings. That question was whether the applied force and duration for a typical, average amount of time of a given manual myofascial technique could be sufficient to induce palpable viscoelastic changes such as tissue deformation in human fasciae. (4)
They developed a three-dimensional mathematical model with equations revealing very large forces, “that outside the normal physiologic range, are required to produce even 1% compression and 1% shear in fascia lata and plantar fascia”. Their conclusion was, The palpable sensations of tissue release that are often reported by osteopathic physicians and other manual therapists cannot be due to deformations produced in the firm tissues of plantar fascia and fascia lata. However, palpable tissue release could result from deformation in softer tissues, such as superficial nasal fascia. (4)
Those authors chose a common manual therapy technique used by osteopaths and other practitioners who, “report local tissue release after the application of a slow manual force to tight fascial areas”. (4) Reduced to its basic mechanical components, the technique used in this study—often called myofascial or fascial release—employed pressure and shear together to treat movement restrictions in specific dense (less elastic) fascial tissues and then in other softer (more elastic) fascial tissues. The combination of pressure and shear produces a stretch of the tissue, often directly into the barrier of restriction that has been variously described by practitioners as getting a plastic, permanent deformation of restricted tissues.
After that study was published, many more articles appeared online with definitive sounding headlines and titles like, “If We Cannot Stretch Fascia, What Are We Doing?”, or even more succinctly, “Reasons not to stretch”. (3,5) From the sound of those titles, it appeared that the controversy of whether fascia can stretch or not was settled. In fact, this is very much not the case.
The 2008 article previously mentioned appeared to provide valid evidence for the case against certain kinds of fascia—plantar fascia and fascia lata—being able to be therapeutically stretched for permanent treatment effect. However, that article also stated at the outset that “palpable tissue release could result from deformation in softer tissues”. (4) Research that “investigated the potential importance of uniaxial tension in a variety of therapies involving mechanical stretch” was considered. (4) This fact—that less dense or “softer” connective tissues could indeed get the release effect from tissue deformation that many practitioners observe—was largely missing from the many articles and blogs that this author came across that questioned or advised whether stretching is necessary.
So although research explained and cited in that 2008 article that determined tissues such as the iliotibial band and the plantar fascia cannot be stretched to get a therapeutic effect without damaging the tissue, that was only true for a certain type of “dense connective tissue” in a specific location that endured peculiar biomechanical forces unique to it. Here are the quotations supporting that fascia does stretch from the original 2003 article by Schleip: (3)
In summary, while we discussed evidence that supports certain types of fascia cannot be therapeutically stretched, we also presented evidence that other types do stretch, via the different kinds of mechanoreceptors that are stimulated when the fascia in which they are embedded is stretched. One cannot stretch a mechanoreceptor in isolation and apart from the connective tissue in which it lies. More about this will be explained in the next section.
More recently, biology has provided much well-established evidence that mammals, including humans, have many examples of stretch-dependent mechanisms that are essential for survival. If we start with just about any cell, the concept of tensegrity is a given in the burgeoning and fascinating field of mechanobiology. (6) Mechanobiology “centers on how cells control their mechanical properties, and how physical forces regulate cellular biochemical responses, a process that is known as mechanotransduction”. (7) Tensegrity (a portmanteau of tension-integrity) depends on tensile prestress for its mechanical stability in biological structures and the physiological systems they drive. As Ingber states, “tensional prestress is a critical governor of cell mechanics and function, and how use of tensegrity by cells contributes to mechanotransduction”. (7) There is also evidence that the stretch-dependent tensegrity model may be applied to the extra cellular matrix:
The ECM, a polymer network consisted [sic] of many different protein polymers, may be viewed as an extended cytoskeleton that connects cells within living tissues and organs. In many soft tissues, the ECM is tensed by adherent living cells that exert traction forces on their adhesions, …this prestressed network essentially stabilizes itself like a tensegrity structure. (7)
In short, from nanoscale to macroscale, evidence shows that cells and the tissues, organs, systems, and organisms they differentiate into are all under a normal state of tension or stretch in the unperturbed steady state at rest that fosters homeostasis, as well as in the more active state of homeokinesis.
Earlier, the fascial system was described as a “three-dimensional continuum of soft, collagen containing, loose and dense fibrous connective tissues that permeate the body”. (1) All of the neural receptors that communicate to the brain and the rest of the central and peripheral nervous systems about gamma and alpha muscle tone (and much more) are embedded within this system that is under tension or stretch at rest as well as during movement. Studies noted previously as well as many more include findings that a majority of those neural receptors fundamentally respond to mechanical stretch to drive cellular communication and physiology that activates life and function in the human body.
After just reviewing a number of previous citations that provided evidence for cell and tissue stretching, we turn to the stretching studies of larger regions of myofasciae of the human body, that is, the “muscles”.
In 1999, a critical review of the clinical and basic science literature arguably started a debate among professionals in health, fitness, and sports about the merits of stretching that continues to this day. Titled, “Stretching before exercise does not reduce the risk of local muscle injury”, it raised the hackles of many practitioners who also incorporated stretching into their work. (8)
Prior to that article, many generally assumed that stretching improved functional and athletic performance, increased flexibility, and reduced injuries. (9) Many practitioners from diverse disciplines were convinced about the importance of stretching as a necessary part of their protocols for successful outcomes. The article questioned belief systems with scientific evidence, which started a tide of controversy and dispute about the actual benefits of stretching.
This tide surged in 2002, when an article that stirred even more controversy appeared. (10) It was a systematic review of research that evaluated the benefits (or lack thereof) associated with stretching procedures in relation to protection from injury and post exercise soreness. Conclusions taken directly from the study were as follows:
Stretching before or after exercising does not confer protection from muscle soreness. Stretching before exercising does not seem to confer a practically useful reduction in the risk of injury, but the generality of this finding needs testing.
In 2003, an article titled, “The stretching debate” surfaced in direct response to the previously discussed review. (11) It featured invited commentary by respected clinicians about the review that was largely negative on the benefits of stretching. Opinions were at times emotionally charged and reflected the conflicts between what many practitioners believed worked for them and what some researchers were claiming was really happening in stretching. Adamant pro and anti-stretch camps formed within professions practicing varietal therapies and also included fitness and sports coaches and trainers. This acrimonious climate was covered by the media, adding more fuel to the fire. (5) The public who was following this controversy were confused about whether they should stretch at all. Their practitioners, coaches, and trainers were not all in agreement about whether stretching should be implemented or if utilized, how to design an appropriate program.
For the next decade, there were published a multitude of studies comparing a variety of set parameters that established poor outcomes when static stretching is done up to an hour before athletic activity requiring power or strength. (12) Yet even as the case for the negative impact of stretching persisted, new studies showing specific benefits began to surface.
One systematic review on multiple studies indicated the following positive outcomes from stretching: (13)
Since the above systematic review was published in 2012, there have been many more studies on stretching that have come out. If we discuss just those studies that are in the “high-quality category”, the choices are unfortunately few. And examples of the practical application of favorable outcomes are severely limited. The following are examples of high quality, starting with the highest: meta analyses, systematic reviews, and randomized controlled trials (RCTs).
This section is limited to discussing the relatively few high-quality studies that present research relevant to practitioners. As stated earlier, there is an abundant of lesser- quality studies available to peruse that have come out in the last 5–10 years.
An analysis of the current literature on the acute effects of dynamic stretching (DS) determined that, “there is a substantial amount of evidence pointing out the positive effects on range of motion (ROM) and subsequent performance” as determined by the measured production of force, power, sprint and jump. (14) As opposed to static stretching which commonly entails holding a position of stretch for a defined period of time, DS is performed with constant motion, into and out of the stretch position. DS in sports is commonly performed at faster tempos pre activity to aid performance and slower tempos post activity to aid recovery.
After years of debate about whether stretching was even appropriate for athletes to engage in, growing numbers of studies were finally pointing to the benefits. Despite a recent systematic review finding minimal evidence presented as to how DS actually affects the neuromuscular system,(15) DS is now considered an essential element of athletic preparation. (9)
Despite substantial amounts of evidence favoring individual and group dynamic stretching, the previously noted analysis also found numerous studies reporting no alteration or even performance impairment. Possible mitigating factors such as stretch duration, amplitude, or velocity were highlighted. However, it may be easily extrapolated that other additional factors such as stretch intensity, frequency, and tempo are also relevant.
A recent collaboration between top stretching researchers produced a systematic review summarizing the results of the high quality RCTs published to date. (15) This review produced a summary of stretching outcomes that provides one a comprehensive impression of where the science of acute, pre activity self stretching may be today.
In this review, “an overview of the literature was performed citing the effects of pre activity stretching on physical performance, injury risk, and ROM, as well as the physiological mechanisms, with the objective of investigating, analyzing, and interpreting the acute physical responses to a variety of stretching techniques to provide clarity regarding the impact on performance, ROM, and injury”. (15)
Limitations described by the authors that were encountered when reviewing the literature included, “issues related to internal validity (i.e., bias caused by expectancy effects) and external validity (i.e., stretch durations and warm up components, description detail of stretches, reporting bias against non-significant results)”.
Based on this systematic review, the authors produced the following position statement for the Canadian Society For Exercise Physiology that has been paraphrased and condensed (15):
Muscle stretching pre activity (done by solitary individuals to themselves or in a group) in some form appears to be of greater benefit than deficit (in terms of performance, ROM, and injury outcomes) but the type of stretching chosen and the make up of the stretch routine will depend on the context within which it is used.
The following contexts were enumerated in the position statement and are followed by this author’s comments:
Comment: Setting individual circumstances aside, this conclusion seems mostly useful for those engaged in rehabilitation to full function that need to make steady progress while simultaneously keeping risk low to none for reinjury. It is the author’s experience with athlete patients, and with colleagues and students working with athletes, that both SS and PNF>60s per muscle is not done at all. Instead DS is used for all pre activity preparation.
Comment: (a) This statement confirms what is commonly practiced today in sport training, i.e., pre activity self stretching with best outcomes for performance is dynamic or DS. (9) However, if an individual is engaged in rehabilitation in order to return to sport activity, the guidelines indicate that if the person has decreased ROM or is recovering from a muscle injury, then an SS and/or PNF program may be indicated while DS is avoided until fully recovered. This author has had success with programs that are often combined, i.e., they address the target tissue or involved region that is recovering with SS or PNF first, then do DS before an activity that is paced and progressed according to the healing phase and ability of the per- son. (b) It is not clear what the statement, “more than 5 min” means, i.e., there is no defined termination point at which time it can be deemed that there is no benefit to a longer duration stretch. (c) Even if multiple muscle groups are engaged in say a sport-specific manner, does it make a difference in what order those movements are produced, and if so, what are those movements for each sport, each team player, an individual with specific or unique needs?
Comment: Because the totality of functional movement in sports entails patterns characteristic of combining concentric shortening with eccentric lengthening, and sometime isometric positioning, a 10% loss in strength in a shortened position seems hardly a reasonable trade-off for a 2% gain in a lengthened position. However, if an athlete is engaged in a sport or in specific training that requires more eccentric strength, it may be deter- mined that SS may be indicated at longer muscle lengths functional for that activity.
Comment: This statement indicates that it is still not known what precise type or manner of stretching may increase or decrease risk of injury. Therefore, more studies are needed.
Comment: This author has clinical experience and testimonials from many students that has confirmed repeatedly that at least one specific type of assisted stretching does reduce and eliminate muscle soreness depending on many factors, including but not limited to sleep deprivation, dehydration, malnutrition, and chronic low-level systemic inflammation. It may be considered that the positive results noted may be from various combinations of parameters peculiar to the specific assisted stretching cited. (12) Further research is warranted to verify.
From reviewing this systematic study as well as the author’s position statement on guidelines for the Canadian Society for Exercise Physiology, this author concludes that there is still insufficient tangible, concrete, or practical information from evidence-based research alone, to design a comprehensive sport or athlete-specific acute self stretch program.
Another opinion offered by a contemporary author who also recently reviewed much of the literature on stretching science has come to a similar, though differently worded conclusion: “There is still much we do not understand and, for now, the conclusions lie somewhere in the middle—stretching is sometimes good, but not that good, and when good, only under certain conditions”. (16)
Coming around full circle from the beginning of this chapter when the controversy of whether fascia could be stretched or not was posited, a high-quality systematic literature review of randomized controlled trials was conducted that looked at the effectiveness of myofascial release, a form of direct and indirect stretching of restricted fasciae. (17) It was concluded that, “MFR is emerging as a strategy with a solid evidence base for the future trials”.
While studies about macro stretching, that is, those that focus on whole body and muscle groups are voluminous, they are of mostly poor quality in terms of research design. Unfortunately, the few that are high quality do not currently offer precise enough guidelines for practitioners to plan complete valid and reliable assisted stretch therapy or self stretch programs for their patients and clients.
While not currently offering practical guidelines either, studies on micro and nano stretching of cells, tissues, and mammals (much of it about fascial tissues) are gathering specific data that will eventually evolve future design of high-quality macro stretch studies.
The burgeoning field of mechanobiology provides a logical reason for this prediction given that it examines fundamental questions of how living cells physically organize themselves from individual molecules to whole organisms and, as some researchers state, “that this provides a mechanism to channel forces from the macroscale to the nanoscale, and to facilitate mechanochemical conversion in living organisms”. (7)
Mechanobiologists have determined that the design principles of tensegrity structure is inherently a tension (or stretch)-based system with functions that govern life- sustaining principles in various organic structures such as polypeptides in proteins; microfilaments, microtubules, and intermediate filaments in the cytoskeleton; cells and ECM in tissues; and bones and muscles. As the authors state, "The shape stability and immediate mechanical responsiveness of all these structures depends on the prestress that is transmitted across their structural elements. Because cells use tensegrity to structure themselves, mechanical forces and physical cues applied at the macroscale can be channeled over stiffened structural elements, and concentrated on individual structures (e.g., focal adhesions) and molecules at the micrometer and nanometer scales. Specifically, the use of structural hierarchies (systems within systems) that span several size scales and are composed of a tensed network of muscles, bones, ECMs, cells, and cytoskeletal filaments that focus stresses in specific mechanotransducer molecules is key to how living cells carry out mechanochemical transduction, which is critical for their growth and function." (7)
Based on the findings and conclusions of researcher Ingber and many others who have worked for decades investigating and applying tensegrity principles in mechanobiology, it can be stated that the human tensional network is a force transmission, mechanotransducive dependent system in which stretching plays a large and crucial role along with other forces to drive most of the physiological processes of life, much less to drive physical movement of the entire body.
Hopefully, this is the kind of science that will enable researchers to comprehensively study stretching from systemic, whole-body effects of the fascial system, to specific fascial tissues, down to cells and molecules that drive those processes of life.
ANN AND CHRIS FREDERICK ON THE SCIENCE OF STRETCHING: