Artist’s depiction of muscles cells and the sarcomeres insides them, the potent little bundles of protein that power muscle tissue.
Dance of the Sarcomeres
A mental picture of muscle knot physiology explains four familiar features of muscle pain
by Paul Ingraham, Vancouver, Canada (qualifications)
EXCERPT This page is an excerpt from a much more detailed tutorial about myofascial trigger points (muscle knots), which creatively explores many other aspects of the science of trigger points.
… many of the flaws in our ‘design’ have a common theme: They arise primarily from evolutionary compromises ...
Downside of Upright, by Jennifer Ackerman, pp126–145
What’s in a knot? An unholy clump of contracted sarcomeres living in a swamp of garbage molecules, waste metabolites. Sarcomeres are the thing: understand sarcomeres and you can make sense of muscles knots. This is absolutely essential for any patient determined to really understand his or her own trigger points, and any therapist who is serious about providing skilful and rational trigger point therapy.
Sarcomeres are the microscopic engines that power muscle tissue, and misbehaving sarcomeres are at the heart of every trigger point. If you understand “sarcomeres,” four important characteristics of trigger points in particular will become clearer and easier to understand:
- why trigger points can be so stubborn
- why applying pressure to them generally tends to help
- why stretching feels good, but does not work any miracles
- why they make your muscles weak
All of these classic trigger point qualities are due to the nature of sarcomeres and their complex interactions. So, what’s a sarcomere, and what does it do?
What’s a sarcomere?
Sarcomeres are the smallest functional unit of muscle physiology, a molecular-scale structure almost like a microscopic muscle itself. Muscles contract because sarcomeres contract.
A trigger point is a patch of tightly contracted sarcomeres. The dysfunctional sarcomeres contract so strongly that they begin to choke off their own blood supply. This causes a build up of waste products that aggravates sensory nerve endings and causes yet more clenching — a vicious cycle called “metabolic crisis.”
Compared to a muscle cell — which is already mind-bogglingly small, you understand, about 10,000 of them across the width of a fingernail — a single sarcomere is like a grain of wheat in a silo.1 On the other hand, sarcomeres are pretty large as molecular-scale structures go. Every sarcomere is a tidy little package of well-organized proteins, and proteins are massive molecules generally, and sarcomere proteins are big even for proteins. If you were the size of a water molecule, you could wander around inside a sarcomere like a mouse in Grand Central Station.2
If you were the size of a water molecule, you could wander around inside a sarcomere like a mouse in Grand Central Station
We do not have a good understanding of how sarcomeres do what they do. People who make a living studying these things face the possibility of never really understanding their subject, of never even seeing a live specimen doing it’s thing — live sarcomeres cannot be directly observed.3
Fortunately, we do know what they do. We know they make the world go round. More accurately, they make us go around the world. And they also make us hurt.
How sarcomeres work
Sarcomeres are long and thin. Wrap a few hundred of them together like a bundle of firewood, and then line that bundle up end to end with a few thousand other sarcomere bundles, and you’ve got yourself a single muscle cell or fibre. Every muscle consists of many muscle fibres, and therefore of many millions of sarcomeres.
The overall structure of a sarcomere is easy to describe: overlapping chains of proteins, like the tines of two forks meshed together. To contract the sarcomere, the proteins grab onto each other and pull, increasing the overlap of the tines. To relax, the proteins “just” let go.4
Sometimes isolated patches of sarcomeres go into spasm independently of the rest of the muscle. We know the general physiological conditions that provoke this change — cold, overstretch, stress, trauma, pain, fatigue — but exactly why these things cause some sarcomeres to hypercontract basically remains a mystery. For whatever reason, the proteins grab onto each other, start to pull … and will not let go. The tines of the fork jam tightly together, completely overlapping and even overshooting each other partially, like interlaced fingers.
This tutorial isn’t a sarcomere tutorial. There are many, many descriptions of sarcomeres out there. This is a primer for beginners, and a refresher course for professionals. I do want you to appreciate just how weird and wonderful sarcomeres are, but what we’re really interested in is how sarcomeres have a starring role in your muscle knots.
Trigger points are like pimples — everyone has at least a few, and everyone gets a bad one every now and then. Knowing what makes them tick is great “owner’s manual” knowledge!
That’s the end of the free excerpt. To read more about the science of sarcomeres, see the full trigger points tutorial, Save Yourself from Trigger Points & Myofascial Pain Syndrome! In the full version, you’ll learn about why pressing on patches of stuck sarcomeres “hurts like hell but feels like heaven” and why it tends to make people say funny things. You’ll learn about how scientists have just recently (2008) confirmed the existence of lots of toxic molecules floating around inside trigger points: “… not just 1 noxious stimulant but 11 of them.” And why is contracting muscles with trigger points like trying to pull away from an intersection in third gear? It’s all in the complete tutorial, plus a great deal more! Buy it now ($19.95) or read the first few sections for free.
Notes
- This was a tough image to come up with. Sarcomeres are about 2.5 microns long, give or take, depending on whether they are contracted or not. That means you can put about 20,000 of them end-to-end in a 5cm long muscle cell, which is pretty much equivalent to grains of wheat stacked about 15,000 deep into a fifty-foot silo. But the comparison gets confusing when comparing diameters. Muscle cells are only about 40–100 microns wide, which makes them about a thousand times longer than they are wide. A fifty foot grain silo with matching proportions would only be about a half inch wide! More like a grain pipe. Still, sarcomeres are also extremely skinny, just like cells. Laid end-to-end, you won’t fit all that many — about 40 — across the diameter of a muscle cell. But sarcomeres are so skinny that the number you can fit side to side across a muscle cell skyrockets and becomes, once again, comparable to the number of grains across the width of a silo. So you really can think of a sarcomere as being the size of a “grain” in a muscle cell “silo”. Return to text.
- Water molecules are ridiculously small. They are measured on the scale of angstroms, which are 10,000 times smaller than microns. So if you’ve got yourself a sarcomere 2.5 microns long, you could line up about 25,000 1-angstrom water molecules in there. Now, how does that compare to a mouse in the Empire State Building? Well, a mouse is about 2cm tall, and the Empire State Building is 381 metres tall. So if you were going to bury the building in mice — assuming, of course, that the mice wouldn’t compress (ew!) — you’d need to bury it about 19,000 mice deep. So the analogy is pretty strong: molecules in sarcomeres are like mice in a skyscraper! Return to text.
- The only way to “see” them in any detail at all is to use an electron microscope, which requires a dead specimen, and even if you could watch the overall shape of a single sarcomere contracting, it still wouldn’t be enough: all the detailed action happens at the atomic scale. It would be like trying to make sense of football game from orbit. In 2001, “the smallest consistent biomechanical event ever demonstrated” — not actually “seen,” just demonstrated — was a 2.3-nanometer long step in the length of a sarcomere (see Blyakhman). That is an impressive one thousandth the size of the sarcomere, but still ten to one hundred times larger than the scale of the smallest units involved, the ions and other smaller non-protein molecules that mediate all of this. And again, this distance was inferred from cryptic and extremely complex data … not “observed.” Return to text.
- Actually, there is nothing “just” about it: how sarcomeres control muscle elongation — what we call an eccentric contraction, which occurs in the biceps when lowering a barbell, for instance — is one of the biggest mysteries of muscle physiology. There is no known mechanism for how a sarcomere’s overlapping proteins can partly hang on to each other, yet still allow themselves to pull apart. See Eccentric Contraction. Return to text.
