Muscle Physiology: How Muscles Lengthen

This is a slightly updated EXCERPT on
muscle physiology, and fascia too, from
Arrow pointing to e-bookmy e-book, The Simple Steps to Let-Go Yoga:
& Neuro-Structural Sciences of Physical/
Mental & Therapeutic Yoga
by David Scott Lynn

What REALLY Makes a Muscle Lengthen?
Some Muscle Physiology

SPECIAL NOTE: It has recently come to my attention that the following explanation of  the muscle physiology of how relaxation & lengthening of musculo-fascial units happens might be considered controversial. Previously, I had merely thought health care practitioners had not observed or thought about, nor understood, this phenomena of very straightforward physiology. I had not even seen it as much of an “issue” at all. I thought it had been just an oversight, and an interesting insight explaining a lot of stuff that few people seemed to have noticed. But for some, this idea apparently strikes at the heart of their beliefs. If it strikes anyone as too controversial or unreasonable, as with all of my other ideas and information, I welcome any interaction on this point-of-view. ~ Thanks, DSL

Neuro-Muscular Contraction

Simply put, muscular contraction is the Creation of Tension & Pulling Force by activation of nerve tonus from brain and central nervous system to the muscles.

Tonus is the bio-electric charge traveling down the nerve to the muscle, causing the muscle to turn ON. When it turns on, the actual generation of force & movement is created by the actin-myosin filaments within the muscle cells.

That’s the most basic aspect of muscle physiology.

Actin-Myosin-Cytoplasm & muscle physiologyThe actin-myosin molecules act a bit like ratchets crawling along each other, like a tube pulling up inside another slightly larger tube, one tube overlapping the other.

[The sliding tube & ratchet metaphor is not precisely accurate. The actin-myosin filaments don’t look much like “tubes.” Their structure is more complex, and many illustrations can be seen on Google Images. (KEYWORD: “actin myosin sliding filament theory<==or click the link.) … But I hope this gets the general idea across.]

muscle physiology & ratcheting in yoga

Inner Workings of a Ratchet

Ratcheting action with teeth in muscle physiology

Please Note the Rigid Teeth

Although not as rigid and dense as the steel in an actual ratchet wrench, the actin-myosin filaments are said to have half the tensile strength of steel wire. That means, they are NOT “elastic” as in “length-able,” and do not “stretch” like rubber bands, at all. And although the myosin or actin filaments are not actually mechanical “teeth,” they create a momentary chemical bond with each other that’s very strong.

SEE Youtube Muscle Cell Animations HERE

Without getting too scientific on you, the “teeth” are actually chemical bonds that in normal states turn ON momentarily and repeatedly, in cycles, to create contraction. Too much nerve tonus to the cells, however, or triggered too often, or for extended periods of time, causes the muscle cells to get “stuck” in the ON position, as in the case of C.E.M.&.N.T. (Chronic, Excess Muscle & Nerve Tension & Stress).

This ratcheting phenomenon of the actin-myosin cells creates all gross, and most subtle, movement in the human body, as well as animals. Rudimentary forms of the actin-myosin phenomena exist at lower levels of biological species, as well. This is truly nature’s own invention of overt physical action.

(There is some evidence that in high pathological states, excess local chemistry can cause an actin-myosin “locking” action without the nerve impulse to the muscle cells. This occurs when ATP is insufficient to participate in the metabolic processes of muscle contraction and relaxation. The extreme example is rigor mortis, where the muscle becomes rigid. That, however, is a very extreme situation and outside the scope of this publication.)

Neuro-Muscular Relaxation

Conversely, muscular relaxation — ideally the opposite of contraction — is the process of Stopping of Creation of Tension & Pulling Force by decreasing or turning OFF the flow of nerve tonus from the brain and central nervous system to the muscles, so the actin-myosin filaments stop “ratcheting,” releasing their chemical-based “grip” on each other. The filaments or “tubes,” held up inside of each other by the ratcheting action, can now slide out from each other, allowing an overall lengthening of the individual muscle unit.

Actin/Myosin Fiber “Ratcheting”:
The Primary Resistance to “Stretching”
According To Muscle Physiolgy

Muscle Physiology of Contraction = Ratchet Action of Actin-Myosin cClls

Resistance to Stretching

Muscle physiology appears to say that it’s total shortening of all actin/myosin units in series within a muscle cell producing significant shortening upon contraction OR, when relaxing, allowing lengthening of a muscle fiber. And until and unless those chemical bonding moments (some times very long moments) in the actin-myosin filaments are turned off sufficiently, the muscle will not lengthen. It will even resist lengthening to the point of tearing.

Given that one muscle cell has the tensile strength of half that of steel wire, put a whole bunch of them together in one muscle belly and that’s quite a bit of resistance to stretching.

The Actin-Myosin Fibers are laid in series with each other within a muscle fiber:

Actin - Myosin Cells in Series in a Cell in Muscle Physiology

Ratcheting Your Way Through Life & Sleep

Most importantly, many, if not most people have a very large number of their actin-myosin “tubes” that are “ratcheting” all day and all night long, day in, day out, never turning off. … That is, among other things, exhausting. And since the ratcheting effect is the active component of C.E.M.&.N.T. (Chronic, Excess Muscle & Nerve Tension & Stress), it’s much of what’s putting so much pressure, tension & stress on the various tissues and systems of your body all the time, as well.

Yet as described earlier, muscle cells produce all overt ACTION and most subtle movement, and are our Vehicle of Self-Expression. In the case of C.E.M.&.N.T., they are in the habit of acting, of being contracted, all the time. So it’s a paradox. Like many things in life, the very mechanism we need to move ourselves through life, taken to excess, becomes our very interference in life.

The Key Insight to the Nature
of Conscious Stretching

Therefore, the Key Insight here is the lengthening or “stretching” of a muscle does not come from any significant levels of elasticity (length-ability) within the muscles or tendons or connective tissue. It’s NOT about waiting for them to stretch out like you wait for taffy to pull or ketchup to flow. The change in the muscles does not just come about when the tissue “just finally gives” you some “flexibility” or restored “elasticity.”

The REAL Change — the Relaxation & Lengthening — comes when you learn how turn OFF nerve tonus from CNS (central nervous system) & brain to the actin-myosin filaments or “ratchets.”

Some people can do this non-consciously. But most of us have to work at it, becoming more conscious of how to do it over time. I started martial arts stretching when I was 13 years old, and yoga stretching when I was 19, and I was doing yoga 3 to 4 hours per day, 4 to 6 days per week, for many extended periods of time in my life.

(Since most children do this very easily, with no effort or thought at all, what we’re really “learning” is how UN-learn or DE-condition the accumulations of tension over-riding the natural ability built into the nervous system at birth. Learning to relax is about DE-contracting neuro-musculo-fascial units, which is the STOPPING of DOING Tension.)

And even now in my later fifties [in 2011], I STILL have to work at it. But I had extensive neuromuscular trauma and injuries from racing motocross in my early to mid-teens and working as a structural steel ironworker for several years that were debilitating to say the least. Even 12 years ago I had to do at least an hour of yoga almost every day just to stay vertical. Now, I can get away with 20 minutes most days, if need be. (I much prefer longer sessions, but logistics sometimes interfere.)

DE-Ratcheting & DE-Contracting

Significant lengthening of a muscle — what FEELS like elasticity — is in actuality the relatively smooth, mechanical change in length by the actin-myosin fibers letting go of and sliding out from each other — the UN-ratcheting and the more-or-less rigid “tubes” becoming less overlapped. In normal circumstances, you turn them on when you need them, to the precise degree(s) you need them, then fully off when you’re done with the intended action.

Muscle physiology says it’s as simple as that, although simple is not always easy. … But for many, after a few years of tension accumulation, not so easy. … Fortunately, this fundamental ability is built in by nature at birth, so it’s about recovering your already existing but inhibited ability, not learning a new one.

Behind the scenes, this is, when it comes to so-called “stretching,” what physical/mental yoga is all about. It’s about developing the skill of intentionally DE-Contracting your muscles with your mind. This, in turn, is a result of learning how to turn off the nerve tonus to the muscle cells — the actin-myosin molecules — so they stop all that darn ratcheting, except when you need them.

“Regular Old Stretching” versus
“Technical Stretching”versus
Yogic DE-Contraction

There are various techniques — Tension Reduction Strategies — developed to discover and recover this skill, many with varying degrees of success. Many of them are little more than technical methods by which to “trick” the nervous system into letting go of at least some of the tonus charge to the muscles. (I call them neuro- tricks, like PNF stretching.)

The primary difference between Regular Old Stretching (hoping and waiting for more “elasticity” or discovering better neuro-tricks) and Yogic or Conscious Stretching is what you do with your mind and nervous system, in at least a somewhat meditative process.

Moving Mind Into Muscles
with Muscle Physiology

It’s about your mind investing itself into the neuro-muscular system, discovering ways to consciously turn off the nerve tonus to the actin-myosin molecules — the muscle cells. It’s important to note this investment of mind into muscles is at least as much a physiological and neurological process as it is a mental one, although the mind, of course, has a lot to do with it.

Not a very romantic way of stating it, but THAT is, I believe, much, most or all of what creates truly deep relaxation from a yogic point-of- view. (There are potential metabolic, nutritional and toxicity issues that can interfere with this body-mind ability, however.) … At the juncture between and including both mind and body, the above described process is at least one primary element of what hatha (physical) yoga combined with jnana (mental) yoga, is all about.

“Moving Your Mind into Your Musculature,
so the Distinction between them Dissolves,
is the Essence of Physical/Mental & Let-Go Yoga”

David Scott Lynn

Hatha (Physical) Yoga and Jnana (Jnana) Yoga are among the few Sanskrit words I use, in that there are no really great English translations of the concepts.

To Summarize: One of the many things The DSL Method of Physical/ Mental Yoga, Let-Go Yoga, Yoga-based, Hands-on Structural Bodywork as well as Tai Chi/ Chi Kung Movement Exercise & Therapy is most overtly about:

Learning the art of reducing nerve tonus to the actin-myosin molecules and overall muscle cells. That is, in many ways, an important NEXUS between the inner and outer world of the human being.

muscle as body-mind nexus & muscle physiology

CLICK HERE to Open New Page with Full Size Image of the Muscle NEXUS

The idea here is to use the above principles, including the muscle physiology, and apply them to any yoga asana or “stretch” you can. There are many books available with many ideas of stretches you can do. Or, there’s a set of stretches in Chapter Four of this book you can use. They are geared for Structural DE-Compression & Postural Balancing.

(An extensive e-Course on how to do yoga and details on a wide range of specific yoga asana will soon be available on the website.)

It’s NOT About “Stretching”
or “Restoring Elasticity”

Actin-myosin molecules have very high tensile strength, meaning they’re very resistant to “stretching” as in true and full elasticity. They have a tremendous capacity to bend or flex, which technically is elasticity according to physics.

Yet as you can see above, the actin-myosin cells are more like mechanical teeth engaging and disengaging, rather than rubber bands shrinking or stretching. Yet because there are so many of these microscopic ratchets operating in a bath of water with a high degree of tissue flexibility (which is very different from extensibility* or elasticity [please see explanation a few paragraphs down] in the sense of stretching a rubber band), they have the functional capacity of smooth, fluid movement. It is literally the water (fluid) within that absorbs and cushions any erratic movement of the actin-myosin cells. In both muscle and fascia, it is the high volume of water, resiliency and flexibility producing the feeling of elasticity, fluidity and the “shock absorber” effect.

The Harmony of Muscle Cells & Fascia

Collectively, as integrated units, muscle cells can lengthen up to 150% of their resting length when they relax, let-go and UN-ratchet. And connective tissue (AKA fascia) — the casings of all the muscle fibers, also converging to become the tendons and attachments to the bones — have a maximum 4 to 7% elasticity before tearing (depending on who you read or talk to). So fascia doesn’t “stretch” much either. Its minimal elasticity is mostly for a shock absorber effect.

But in fact, just using the word “stretch” can be misleading to your own mind. If you are not careful, you can fall into waiting for that “elusive elasticity.” Yes, your muscles might somehow figure out how to “relax” on their own without your investing mental power. But I wouldn’t bank on it.

* Extensibility, Elasticity & Flexibility

Extensibility means the tissue can lengthen then return to original length without permanently distorting it’s structure. … Spandex or rubber bands are examples.

Flexibility means tissue can bend and return to normal without distorting it’s structure. A leather or cloth belt is very flexible, but not extensible. Meaning that your belt will not lengthen when you pull on the ends. Yet you can tie it into knots due to its flexibility.

Elasticity has a wider range of meaning than just extensibility, but in the case of muscles and fascia, the more descriptive terms are plasticity, bend-ability and resilience, with very little extensibility. The actin and myosin fibers have LOTS of bend-ability or flexibility, but themselves are not much extensible. Meaning the actin fibers are not extensible, and the myosin fibers are not extensible. It is their interactions with each other ‚ the ratcheting effect — producing the sense or feeling of extensibility of a muscle cell.

More On Fascia

Fascia is only a little more extensible or elastic than actin OR myosin fibers, but are also very flexible. (Remember the apparent “extensibility” of a muscle cell is due to the ratcheting interaction of the actin & myosin cells, NOT due to extensibility of individual actin fibers or myosin fibers.)

Fascia is also much tougher than muscle cells, and serves to support and protect the paradoxically delicate actin-myosin molecules. More importantly for our purposes here, fascia becomes tendon, and tendon attaches to bone. It is the strength and minimal extensibility of tendons allowing them to transfer most of the force generated by the actin-myosin units to the bones.

“Stretchy” Fascia Would Be VERY Inefficient

If tendons and fascia were very extensible (“stretchy”), the actin-myosin cells would have to contract much more to create movement. Nature, in its wisdom, created the division of labor, giving the two kinds of tissue very different jobs in life.This is basic muscle physiology & structure.

(The paradox is actin-myosin muscle molecules are extremely fragile compared to fascia, yet actin-myosin cells are what generate almost all the pulling power & force. They have a very distinct differentiation and division of labor producing a phenomenal diversity of movement and protection of the human body.)

Muscles Are Not Rubber Bands

My main intent here is to not use words giving you any impression that musculo-fascial units are in any way like rubber bands, taffy, spandex or other kinds of “stretchy” phenomena.

It’s not exactly an illusion, but if you treat your muscles as if they were like rubber bands or taffy waiting to stretch out (meaning not working directly with the fact that it is the nervous system keeping the actin-myosin cells engaged and reduced ability to lengthen), you’ll get little or no results at best, or you can damage your self at worst.

You do NOT want to forcefully tug on the ends of your muscles thinking or hoping that that force is what’s making them “stretch out.” Because forceful stretching actually (usually) triggers a stretch reflex, such actions actually make the muscle cells contract even more.

(The science says stretch reflexes can e overridden by higher brain center activity. This probably takes some time and training, however.)

NOTE on TITIN: The only significantly elastic portion, as in extensibility, of a muscle unit — called titin — is only fully accessed as to “elastic stretchiness” when tonus in neuro-muscular units are turned nearly or completely off, a very rare event for most people in modern society, including many very flexible gymnasts, ballet dancers & top-rate yoga teachers. This is because of their increased Resting Tonus, discussed above in Premise #3, Chapter One of Simple Steps to Let-Go Yoga (his e-book.)

Fascia Does NOT “Relax”

You cannot truly relax, in the psycho-neuro-muscular sense, anything but your muscles. You cannot, for example, “relax” your fascia in the neurological sense because in the fascia, there are very few if any motor (on/off) control nerves, nor any significant numbers of neuro-contractile fibers, communicating with the fascia. Fascia has a tremendous amount of sensory nerve embedded in it, sending vast amounts of important data to the central nervous system.

But fascia can only relax as would a rope “relax” if you stopped pulling on the ends of it, as fascia “relaxes” in that sense when the muscle cells stop generating contractile force. (The word “relax” has multiple meanings, and can lead to confusion.)

“Hardening” versus “Contracting”

One theoretical possibility of muscle physiology applied to fascia is yet to be substantially proven. It is sad that fascia has a piezo-electric aspect. According to modern research, it is possible that in certain conditions, when a piezo-electric stimulation arrives to the fascial tissues, that charge will cause fascia to “tense” or harden a slight amount. This would make sense in that this momentary tensing might provide more support or added protection to the functions of the actin-myosin units and other organs wrapped in fascia.

Yet this is only theoretical at this point.

“Stretching the Fascia”

So, when people say they are “stretching the fascia” or “stretching the connective tissue” independently of the muscles, well, you don’t have to say anything, but that is, most likely, an illusion.

This includes some manual therapies, such as various and so-called Fascial Release Techniques. In reality, they are stretching the fully integrated and inseparable, structural units of function called the musculo-fascial system, which just happens to be a critical part of the bigger system the psycho- neuro-musculo-fascial-skeletal system.


If information and insight like the above are of interest to you, such as extensive muscle physiology, as well as structure & function of nerves and fascia, and much, much more, please check out my e-book:

Simple Steps To Let-Go Yoga …

It’s a Technical Manual of principles & practices of modern postural yoga and the sciences behind them.

Front cover for Simple Steps to Let-Go Yoga e-book


CLICK HERE (or on the image to the Left)
to Read About DSL’s New e-Book:
The Simple Steps to Let-Go Yoga
And the Neuro-Structural Sciences
of Physical / Mental and
Therapeutic Yoga

 “I read David Scott Lynn’s book which I highly recommend for every massage therapist. I was amazed at how intricately he delves into and emphasizes, over and over from various angles, how our work mostly works to affect the nervous system in a variety of ways.
He explains ‘nervous system to myofascial relationships’ brilliantly!”

Dr. Michael A Koplen, DC
Santa Cruz Area, California

==>OR, You Can Go Directly To The Purchase Page HERE<==

SPECIAL NOTICE: I am currently running a SPECIAL BONUS OFFER where you can get FIVE more of my yoga-related e-books still in Pre-Publication state. They are in need of editing, formatting and updating. But the basic info is there, and you’ll get the newer versions when done for no extra charge. … I’ll send the Bonus e-Books to your e-mail address within 24 hours of your purchasing The Simple Steps To Let-Go Yoga. ~ Thanks, DSL

CONTACT David Scott Lynn

Many Thanks for Reading,
David Scott Lynn (DSL*)
* DSL: Your Hi-Touch Up-Link to the Inner-Net
Inner-Net: Your Psycho-Neuro-Musculo-Fascial System

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David Scott Lynn (DSL)

DSL the Yogi at Whole Life Perspectives
Beginning at 13 years of age, DSL's been involved with alternative philosophies & practices most of his life. Becoming a yoga teacher in 1976, then a hands-on bodyworker in 1981, he developed a unique & highly effective form of Yoga / Bodywork / Whole Health Fitness & Therapeutics. … David wrote the chapters on a wholistic philosophy & physiology of bodywork & stretching for the textbook Structural Balancing, published by McGraw-Hill, Inc. in 2010. … He is the author of Simple Steps to Let-Go Yoga, available at: … Several other e-books and e-courses are soon forthcoming at … David consults with Kyle C. Wright on massage school development at the Schools of Advanced Bodywork at .
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