For a long time, our explanation of human movement was remarkably tidy. Muscles had origins and insertions, each muscle had a list of actions, bones acted as levers, and if we wanted to understand a movement we could, at least in theory, identify the muscles involved and add their individual contributions together.
That model was useful. It still is. But like most models, it simplified reality.
Over the last few decades, fascia research has helped expose some of those limitations. We now have much more reason to think of muscles as structures embedded within a larger connective-tissue network rather than independent motors operating beside one another. Fascia is mechanically active, richly innervated, adaptable to loading, and involved in interactions between structures that traditional anatomy often presents as separate. A major sports-medicine consensus described the ''fascial system'' broadly as a body-wide continuum of collagen-containing connective tissues that contributes to the integrated operation of body systems.
That shift in thinking was important. The problem is that the pendulum may now be swinging in the opposite direction.
Spend enough time around sports performance today and you will hear about fascial lines, fascial slings, biotensegrity, elastic recoil, energy storage, force transmission and “capturing energy.” None of those concepts is automatically wrong. The difficulty begins when a useful concept gradually becomes a specific explanation for what an athlete is doing, even when we have not actually measured the structure or mechanism being credited.
Fascial continuity is real. Myofascial force transmission is real. Elastic behavior is real. But a mechanism can exist without being **the dominant mechanism** behind the movement we are watching.
That distinction is the point of this article.
1. First, what do we actually mean by fascia?
Even the definition is less straightforward than it sounds.
The word ''fascia'' can refer more narrowly to identifiable anatomical sheets and layers of connective tissue. The broader term ''fascial system'', increasingly used in research and sports medicine, includes a much larger continuum of collagen-rich connective tissues. Depending on the nomenclature being used, that broader system can include superficial and deep fascia, intramuscular connective tissues, aponeuroses, tendons and other structures that mechanically connect different regions of the body.
That distinction is worth making because the fascia is not simply the white wrapping we remove from a muscle during an anatomy dissection.
Inside skeletal muscle, connective tissue is already everywhere. Individual muscle fibers are surrounded by endomysium, groups of fibers are organized by perimysium, and the muscle itself is surrounded by epimysial connective tissue. Those structures interact with aponeuroses and tendons to transmit force both along and across muscle architecture.
The boundary between “muscle” and “connective tissue” is therefore much cleaner in a textbook illustration than it is mechanically in a living human being.
Fascial tissue is also not one uniform material. A 2024 study examining samples of ''human superficial fascia ex vivo'', for example, found clear differences according to anatomical region and loading direction. The tissue demonstrated anisotropic behavior — meaning that its mechanical response depended on the direction of loading — as well as viscoelastic stress relaxation. Importantly, that study involved tissue samples from four donors, so it should not be treated as a universal description of every fascial structure in every athlete. It does, however, illustrate why talking about “the fascia” as though it had one stiffness or one mechanical behavior is problematic.
Fascia is biologically active too. A systematic review of fascial innervation found free nerve endings along with ''Ruffini and Pacini type'' structures in several fascial tissues. The distribution varied substantially between regions, and pathological fascia often showed different innervation patterns from healthy tissue. This supports a role for fascia in nociception and suggests a contribution to proprioceptive and other sensory information, but it does not tell us how large that contribution is during a specific sporting movement compared with muscle spindles, skin receptors, joints, vision or the vestibular system.
Fascial tissues can also respond biologically to mechanical loading. Mechanotransduction provides a route through which mechanical stimuli influence cellular signaling and extracellular-matrix behavior. But this area is still developing. A recent narrative review specifically noted that there is no universally established mechanotransduction framework for fascia and that we still lack reliable quantitative thresholds distinguishing adaptive from potentially pathological loading.
So fascia is neither passive packaging nor a magical elastic suit.
It is heterogeneous, mechanically relevant, innervated and adaptable.
Most importantly, it is integrated with everything around it.
2. What Thomas Myers actually proposed
Thomas Myers and ''Anatomy Trains'' had a huge influence on how therapists, movement professionals and eventually coaches began thinking about connective tissue.
His idea was developed in the 1990s and organized anatomical continuities into a series of ''myofascial meridians''. Today, Anatomy Trains describes twelve principal meridians and presents them as an “anatomy of connection”: a way of thinking beyond isolated muscles when assessing posture and movement.
The illustrations became enormously influential.
Most performance coaches have probably seen the Superficial Back Line, Spiral Line, Functional Lines and other recognizable pathways drawn across the body. They are visually intuitive, easy to remember and far more appealing than looking at dozens of individual muscles in isolation.
But something important gets lost when we separate the images from Myers’ explanation of them.
They are ''myofascial'' meridians. Not simply “fascial lines.”
Anatomy Trains itself explains ''myofascia'' in terms of the bundled, inseparable relationship between muscle and its accompanying connective-tissue network. The meridians are presented as a practical framework for clinicians to think about connectivity, palpation and movement.
That is quite different from imagining a fascial cable running from one end of the body to another independently of the muscles along the route.
Myers also does not appear to be moving toward a more isolated fascia-based explanation of movement as his thinking develops. If anything, he has moved further toward systems language. Anatomy Trains describes a global ''neuromyofascial web'', and in a May 2026 public commentary Myers explicitly framed the “fascial idea” primarily as a systems concept concerned with relationships and interaction rather than isolated anatomical objects. That article is Myers’ philosophical commentary, not a scientific consensus statement, but it is useful for understanding how he currently frames his own work.
And that makes what happened next particularly interesting. ''Anatomy Trains gave us a map of connections.'' Somewhere along the way, parts of the performance world began treating the map more like a wiring diagram.
3. Did science validate the lines?
This is where any serious discussion has to resist the temptation to choose a team.
Saying “fascial lines are nonsense” would be just as careless as saying that every line drawn in Anatomy Trains is a proven functional pathway during athletic movement.
There is anatomical evidence supporting several proposed myofascial continuities. Research examining these chains has found stronger support for some routes than for others, and a 2025 narrative review concluded that anatomical support is strongest for the Superficial Back Line and the Front and Back Functional Lines, more moderate for some others, while the Superficial Front Line has not received equivalent validation. The same review described functional evidence as emerging but emphasized that human evidence quantifying epimuscular myofascial force transmission remains limited.
Specific dissections are also instructive. Wilke and colleagues, for example, demonstrated morphological continuity between the iliotibial tract, crural fascia and fascia associated with the fibularis longus. When tension was applied during dissection, local tissue movement could be observed across the connection. But the authors were careful about the next step: they called for biomechanical studies capable of quantifying the amount of tensile transmission before its importance to locomotion could be established.
That is exactly the distinction we need to preserve. An anatomical study can answer: ''- Are these structures connected?''
It may provide evidence that tension ''can'' cross that connection. But it does not automatically answer:
''- How much force travels through it in vivo?''
''- How much does that contribution matter during a particular task?''
''- Is that pathway more important than the many other routes through which forces are being transmitted?''
And certainly not: ''Is this the dominant mechanism behind a baseball swing?''
Those are different research questions.
4. How a useful idea becomes a narrative
This is where I think the performance world occasionally gets ahead of the evidence. Imagine that research identifies an anatomical continuity between structures represented in a proposed myofascial line. That is the first observation. From there, the conversation can quietly evolve:
- There is anatomical continuity.
- So the line transmits force.
- The athlete therefore loads the line.
- The athlete stores energy in the line.
- The athlete then recoils through the line.
Eventually, we arrive at the idea that we should specifically train the athlete’s “fascial sling.”
Nothing in that progression sounds ridiculous. In fact, that is precisely why these narratives are so persuasive. The problem is that every step adds a little more functional specificity than the one before it. By the time we reach the end, we may be claiming something far more precise than the original evidence established.
Elastic recoil is a good example. Humans unquestionably store and return elastic energy during movement, but describing that process as primarily “fascial” creates an attribution problem. Tendons behave elastically. Aponeuroses deform. Intramuscular connective tissue contributes to force transmission. Muscle fibers change length and produce active force. Joint position changes the mechanical environment, while neural control determines the timing and magnitude of muscular force.
Recent work on aponeuroses makes the problem particularly clear. Aponeuroses are collagen-rich connective tissues linking muscle fascicles to tendons, but their mechanical behavior is anything but simple. A 2026 review describes them as experiencing multidirectional and spatially heterogeneous loading, with deformation changing according to muscle force, length and activation. The authors also emphasize how much remains unresolved about their function *in vivo*.
If we cannot fully describe what is happening mechanically even inside the muscle–aponeurosis–tendon unit during contraction, we should probably be cautious about watching a high-speed swing and announcing that the recoil we see is coming from a particular fascial line.
The athlete may absolutely be storing and returning energy. The question is whether we know ''where'', ''how much'', and ''through which structures''. Usually, observation alone cannot answer that.
5. Force transmission is real. The magnitude is the harder question.
One of the most compelling reasons to move beyond an isolated-muscle model is that evidence of mechanical interaction between neighboring muscles exists in humans.
Yoshitake and colleagues manipulated the length of the biceps brachii while measuring the shear modulus of the adjacent, resting brachialis. Because those muscles have distinct distal tendons, changes detected in the brachialis as biceps length changed were interpreted as evidence of epimuscular myofascial force transmission. The response also varied regionally and appeared stronger under certain muscle-length conditions.
That is important evidence. But it is not the whole story.
A different human experiment examining the flexor pollicis longus and the index-finger portion of flexor digitorum profundus found evidence consistent with intermuscular force transmission, yet concluded that the amount attributable to passive stretching of the adjacent muscle was probably small enough to ignore under those experimental conditions.
Those studies are not contradictory. Together, they illustrate exactly why this subject needs nuance.
Force transmission can exist without necessarily being large enough to dominate function.
Its magnitude and relevance appear to depend on anatomy, muscle length, loading conditions, region and the task being studied. Human evidence is growing, but it remains far from allowing us to draw a colored line over an athlete and assign a known percentage of force transmission to it.
So when someone says, “force is traveling through this fascial sling,” the appropriate scientific response is not necessarily “no.” It is:
- How much?
- Under what conditions?
- Compared with what?
- And how was it measured?
Those questions are not semantics. They determine whether we are discussing a plausible mechanism or a demonstrated contributor to performance.
6. The more we understand fascia, the harder it becomes to separate it from muscle
There is an interesting paradox in fascia research. The more seriously we take connective tissue, the less useful it becomes to talk about “muscle versus fascia.”
A muscle fiber produces active force through actin–myosin interactions, but that fiber is surrounded by connective tissue. Force is transferred into structures around it, through aponeuroses and eventually into tendons, while neighboring structures can also interact mechanically. This does not mean muscle physiology has somehow become obsolete.
- Motor units still matter.
- Muscle architecture still matters.
- Tendons still matter.
- Joint mechanics still matter.
- Neural recruitment and timing still matter.
What changes is our understanding of the boundaries.
The old reductionist model could make it appear as though individual muscles were independent motors pulling on bones. A newer fascia narrative can make the opposite error by imagining fascial slings as independent elastic cables transmitting energy around those muscles.
Both models isolate something that operates as part of a larger system.
Even Myers’ terminology points toward that conclusion. The *myo* cannot conveniently be removed from the *fascia*. Anatomy Trains’ own description stresses their inseparability, while its broader language refers to a neuromyofascial web rather than a fascia-only mechanism.
Perhaps the most accurate question is therefore not: “Is this muscle or fascia?” but:
“What is the behavior of the integrated muscle–connective-tissue system under this particular task and loading condition?”
That question is less marketable. It is also much closer to the biology.
7. Fascia does more than transmit force
Another limitation of the performance discussion is that fascia is often reduced to some form of elastic force-transfer system. That misses much of what makes it interesting.
Fascial tissues are innervated, and the available histological evidence supports roles in nociception and sensory signaling. Again, the contribution is not identical across every fascia, and identifying receptors in a tissue is not the same as demonstrating that fascia is the primary proprioceptive organ controlling a sporting movement. But it is clearly more than passive wrapping.
Fascial structures also need to move relative to neighboring tissues. Hyaluronan-rich loose connective tissue is found at interfaces between deep fascia and muscle and between fascial layers. Research from the Stecco group has described cells they termed ''fasciacytes'', associated with production of this hyaluronan-rich extracellular matrix and potentially with regulation of fascial gliding.
Then there is the cellular response to mechanical loading. Mechanotransduction gives us a plausible biological route through which repeated mechanical environments can influence connective-tissue remodeling over time. What it does ''not'' give us is permission to claim that a few minutes of pressure, stretching or one particular exercise immediately “reorganizes the fascia.” The molecular literature is interesting, but the dose-response relationships and tissue-specific thresholds required for many practical claims are still unresolved.
So fascia participates in mechanical interaction, sensory signaling, gliding and tissue adaptation. But once again, ''participation is not the same as dominance''.
8. What we know, and what we are inferring
This may be the simplest way to keep the discussion honest.
What the evidence supports:
- Anatomical continuity exists between many myofascial structures.
- Epimuscular myofascial force transmission has been demonstrated in humans under controlled conditions.
- Fascial tissues are innervated.
- Tendons, aponeuroses and some fascial structures deform under load and can contribute to elastic mechanical behavior.
- Fascial tissues can adapt and remodel in response to repeated mechanical environments.
What those findings do not automatically tell us:
- They do not tell us which tissue dominates a swing or a throw.
- They do not tell us how much force travels through one proposed fascial line during a pitch.
- They do not allow us to determine from video whether the recoil we observe came mainly from fascia, tendon, aponeurosis, muscle or the interaction between them.
- They do not establish that one athlete “uses more fascia” than another.
- And if an athlete moves differently after an intervention, the change itself does not tell us which tissue was primarily responsible.
That is the difference between ''measurement and inference''. And it is where much of the current narrative becomes vulnerable.
9. What can we actually measure?
Modern sports science gives us a remarkable amount of information about athletes. We can measure ground-reaction forces and segmental kinematics. We can calculate joint kinetics and model joint power. We can record muscle electrical activity with EMG. Ultrasound can track muscle fascicles and tendon deformation. Elastography can estimate local tissue mechanical properties under controlled conditions.
All of those tools are useful. None of them gives us a tissue-by-tissue accounting statement during a baseball swing. We cannot watch a hitter rotate and determine that the movement was 40% muscle, 25% tendon, 20% aponeurosis and 15% fascia.
More importantly, we cannot look at an efficient movement pattern and infer those percentages from its appearance.
Even studies investigating epimuscular myofascial interactions in humans require carefully controlled joint manipulations and indirect measures such as shear modulus.
That leads to a principle that applies far beyond fascia:
- Observable behavior is not the same thing as an identified biological mechanism.
If we measure stiffness, we have measured stiffness. If we see rapid recoil, we have observed recoil. If a kinetic model suggests energy is being absorbed and generated between segments, that tells us something about segmental mechanics. The biological explanation comes next. And it requires evidence of its own.
10. What does this mean for baseball and softball coaches?
None of this is an argument for ignoring fascia. Quite the opposite.
A better understanding of connective tissue should make us more curious about how the athlete organizes movement, not more certain that one structure explains everything.
During a swing or throw, muscle fibers are producing force while surrounding connective tissues are deforming. Aponeuroses and tendons are changing shape and tension. Joint positions alter the mechanical conditions of those tissues. Neural control determines when muscles become active and how force develops. Sensory information continuously modifies the solution.
There is no moment where the muscle finishes its job and “the fascia takes over.” It is happening together.
That changes the questions we should ask.
Instead of asking, “Which fascial sling is this hitter using?”, perhaps the more useful question is, “How is this athlete organizing rotation, stiffness, timing and force production to solve the task?”
Instead of asking, “How do we train this fascial line?”, ask, “What mechanical behavior are we trying to influence, and what evidence tells us this athlete needs it?”
Instead of deciding that an athlete lacks “fascial recoil,” ask where energy appears to be absorbed, redirected or lost and whether we have a measurable variable that supports the observation.
These questions are admittedly less exciting than a colored anatomical line running from one foot to the opposite shoulder. But they give the athlete room to be an athlete instead of forcing the athlete to behave like the diagram.
11. The map is useful. It just isn't the territory.
Thomas Myers deserves credit for helping move the conversation beyond isolated muscles.
The idea that connective tissue creates meaningful relationships between structures has held up far better than a purely reductionist view of movement. Some proposed myofascial continuities have anatomical support, human evidence of epimuscular force transmission exists, and our understanding of fascia as a mechanical, biological and sensory tissue continues to grow.
But a map is valuable partly because it simplifies something that would otherwise be impossible to visualize. That simplification becomes dangerous only when we forget that it is a simplification.
Think of a subway map. It tells you that two stations are connected and gives you a useful representation of possible routes through a city. It does not tell you how many passengers traveled between those stations today, how much traffic took another route, why a passenger chose that particular line, or which route was most important to the functioning of the city.
A myofascial map has a similar limitation. It can show or hypothesize continuity. It can help us think globally. It can generate useful questions. But the drawing itself cannot tell us how much force passed through that pathway during a 95-mph fastball or a high-velocity softball swing. That requires another level of evidence.
''Anatomical continuity does not automatically establish mechanical force transmission. Mechanical force transmission does not automatically establish functional relevance during a task. And functional relevance does not automatically establish a dominant performance mechanism.'' That progression is probably the most important thing for coaches to understand.
Conclusion: Fascia Doesn't Need Magic to Matter
Fascia has earned its place in the conversation about human movement.
It connects structures, deforms under load, participates in force transmission, contains sensory innervation, facilitates relationships between tissue layers and adapts biologically to its mechanical environment.
None of that needs to be exaggerated to be interesting. The mistake of the old muscle-centered model was often to treat muscles as isolated components. We should be careful not to repeat exactly the same mistake with fascia.
Human movement is not produced by a collection of anatomical structures taking turns. It emerges from the interaction of nervous, muscular and connective-tissue systems responding to the individual, the environment and the task.
So the goal should not be to replace the muscle story with a fascia story. The goal should be to tell a better story about the SYSTEM.
For coaches, that starts with a simple discipline: observe what the athlete actually does, measure what we can measure, separate evidence from interpretation, and resist the temptation to give every interesting movement an anatomical explanation that we cannot actually demonstrate.
A mechanism can be real without being THE MECHANISM. And if we cannot isolate the tissue, we should be very careful about isolating the explanation.
Refs:
[1]: https://pubmed.ncbi.nlm.nih.gov/30072398/ "Fascial tissue research in sports medicine: from molecules to tissue adaptation, injury and diagnostics: consensus statement - PubMed"
[2]: https://pubmed.ncbi.nlm.nih.gov/38914036/?utm_source=chatgpt.com "Biomechanical properties of the human superficial fascia: Site-specific variability and anisotropy of abdominal and thoracic regions"
[3]: https://pubmed.ncbi.nlm.nih.gov/35628484/ "Fascial Innervation: A Systematic Review of the Literature - PubMed"
[4]: https://pubmed.ncbi.nlm.nih.gov/41516037/ "Understanding Fascial Tissue on the Molecular Level-How Its Unique Properties Enable Adaptation or Dysfunction"
[5]: https://www.anatomytrains.com/about-us/ "Whole-Body Fascial and Myofascial Linkage - About Anatomy Trains"
[6]: https://watch.anatomytrains.com/myofascial-meridians "Myofascial Meridians - Anatomy Trains Video Subscription"
[7]: https://pubmed.ncbi.nlm.nih.gov/41316622/ "Myofascial continuity: Review of anatomical and functional evidence"
[8]: https://pubmed.ncbi.nlm.nih.gov/26522465/Anatomical study of the morphological continuity between iliotibial tract and the fibularis longus fascia"
[9]: https://pubmed.ncbi.nlm.nih.gov/42341705/ "Mechanics of aponeurosis and its role in muscle contraction: current insights and future directions"
[10]: https://pubmed.ncbi.nlm.nih.gov/29776820/ "Mechanical interaction between neighboring muscles in human upper limb: Evidence for epimuscular myofascial force transmission in humans"
[11]: https://pubmed.ncbi.nlm.nih.gov/30768639/ "Minimal force transmission between human thumb and index finger muscles under passive conditions"
[12]: https://pubmed.ncbi.nlm.nih.gov/29575206/ "The fasciacytes: A new cell devoted to fascial gliding regulation - PubMed"