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Eccentric Contraction

A weird bit of muscle physiology

updated (first published 2007)
by Paul Ingraham, Vancouver, Canadabio
I am a science writer and a former Registered Massage Therapist with a decade of experience treating tough pain cases. I was the Assistant Editor of ScienceBasedMedicine.org for several years. I’ve written hundreds of articles and several books, and I’m known for readable but heavily referenced analysis, with a touch of sass. I am a runner and ultimate player. • more about memore about PainScience.com

SUMMARY

An eccentric or braking contraction is an interesting but routine type of muscular contraction that seems like a paradox: the muscle is contracting even as it is lengthening! Eccentric contraction is a bit physiologically mysterious, and is known to be harder on muscle, causing more soreness (quadriceps after hiking down a mountain is the classic example) — a good stimulus to adaptation, in tendon as well as muscle.

full article 1700 words

When you think of a muscle contraction, you usually think of a muscle getting shorter, which is called “concentric” contraction — but that’s not always what happens. We can also do “isometric” contractions, in which there’s no change in length, AKA “clenching.” And then there’s the weird one, a mysterious but routine bit of muscle trickery known as “eccentric” contraction, and it is odd indeed: contraction while lengthening, also sometimes called a braking contraction.

How is this possible? How can that even be called a “contraction”?1 Good question! This is one of the classic examples of a small but persistent mystery of biology. In this age of science fiction body scans and custom-built medicinal molecules, no one really knows quite how eccentric contraction works. The theory of muscle contraction — the sarcomere model, more on this below — is impressive but inadequate.

concentric contraction = contraction while shortening
isometric contraction = contraction without changing length (“clenching”)
eccentric contraction = contraction while lengthening (“braking”)

What is an eccentric contraction used for?

Even if no one knows how it works, it’s easy to understand why you need eccentric contraction: we regularly need to control, slow-down the lengthening of a muscle, a “braking” contraction.

The simplest example of an eccentric contraction is lowering a barbell in a biceps curl. Obviously the biceps muscle contracts to lift the barbell up. But it’s also contracting as you lower the weight — if it weren’t, you would drop it pretty fast! The contraction is not quite strong enough to stop the lengthening of the muscle. The contraction is just strong enough to put the brakes on the lengthening of the muscle.

Here are three sneakier, less obvious examples:

Notice that all three of these examples correspond to body parts that tend to get sore after exercising. Your shins hurt after your first hard-surface run in a while, your quadriceps hurt after climbing down a mountain, and the back of your forearm hurts after your first couple tennis games of the year.

A giant protein probably explains eccentric contraction

A muscle is made of microscopic contractile units arranged in series and bundles: the sarcomeres, tiny packages of proteins (actin and myosin, very famous molecules). Muscles contract because sarcomeres contract. Sarcomeres are little microscopic muscles-within-muscles. Micro muscles. These molecular machines are the best example of how life is chemistry. Although proteins have many impressive properties and do many dazzling things, none is more defining of living things than this ability to generate movement.2

It’s possible that eccentric contractions are a kind of hack, a software solution, a clever way of using the same protein hardware that all contractions use. Or a car metaphor: same motor, different way of driving.

But never bet against molecular machines. It’s always been clear that sarcomeres couldn’t explain everything about muscle behaviour with the actin and myosin proteins alone, and that muscle might well make use of other proteins with other properties. And indeed there is now much more evidence that another big organic molecule, titin, can explain the most puzzling properties of eccentric contraction.3

Basically, muscle behaves as if it’s elastic, and that is hard to explain if you only know about actin and myosin. But titin stiffens in proportion to the strength of muscle contraction, which fits the bill: titin is “loose” and allows lengthening when the muscle is relaxed, but as you power-up the muscle, it stiffens and resists elongation more and more as you clench. Clever.

Eccentric exercise (EE) contraction hurts!

Other than intellectual interest, this is why you should care about eccentric contractions: because they hurt more! Which is both good and bad news. The pain is the cost of an interesting benefit: eccentric contractions are a more efficient way to exercise muscles than concentric. That can make EE useful for rehab,45 but also means that it's easy to overdo it.

Anyone who has ever exercised knows about that nasty soreness that comes on a few hours later. The muscle is weak and sensitive to contraction until you recover after two or three days. This phenomenon is called delayed-onset muscle soreness … and it’s much worse in muscles that have been worked hard eccentrically. That’s why your shins are sore after running hard on concrete, why your quadriceps are sore after climbing down a mountain, and why your forearms are sore after your first tennis match in a year.

Any kind of contraction can cause DOMS, but eccentric contractions will get you there quicker. And there’s no cure for it except to get it over with! Because no one really understands DOMS … although that may finally be starting to change, just in the last few years.6 For more information, see Post-Exercise, Delayed-Onset Muscle Soreness: The biology & treatment of “muscle fever,” the deep muscle soreness that surges 24-48 hours after an unfamiliar workout intensity

Related: two ways to clench?

Isometric contraction is not as exotic as eccentric, but it has its mysteries as well. A 2017 study suggests that there are probably two ways to clench.7

Is there a difference between preventing an object from moving and pressing on a fixed object with the same force? You wouldn’t think so, if the amount of force required is truly the same, but apparently there is. The experiment clearly shows that a “holding” contraction is more exhausting than pushing equally hard on a stable object, demonstrating that “there are probably two forms of isometric muscle action.” Isometric contraction is contraction without movement. Both of these contractions are isometric — there’s no movement, and the forces are the same — but one of them is more tiring than the other.

It’s the difference between pushing on a wall versus trying to stop a moving wall… which sounds like a silly analogy, but the Star Wars trash compactor scene is a perfect example: “The walls are moving!”

Schaefer et al suggest some possible reasons for the difference, such as “complexity of neural control strategies” — in other words, adjusting your force to match an externally applied force may be more of a neuromuscular juggling act than applying a steady force to a stable object.

Interesting as this is, despit the measurable differences I think it might be overstating it to declare that there are two different “types” of contraction. This seems more like evidence that the same kind of contraction is simply more exhausting in one context than another.


About Paul Ingraham

Headshot of Paul Ingraham, short hair, neat beard, suit jacket.

I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.

Related Reading

This article is part of the Biological Literacy series — fun explorations of how the human body works, what I think of as “owner’s manual stuff.” Here are ten of the most popular articles on this theme:

What’s new in this article?

MayTwo new sections, about titin and isometric contractions, and numerous other minor improvements.

Notes

  1. It is an oxymoron if you only use the conventional sense of “contraction,” but there is a technical meaning of “contraction” that is well established and makes more sense. BACK TO TEXT
  2. Hoffmann PM. Life's Ratchet: How molecular machines extract order from chaos. New York: Basic Books; 2012. A wonderful but difficult read about the dazzlingly complicated chemistry and nanoscale “machines” that are the most basic explanation for how living things work. As books go, it doesn’t get much more difficult or rewarding. Although the history of science will bore many readers, it’s impossible to appreciate what we know about know today without hearing the story of how we got here. It is amazing how much we figured out by inference decades, centuries, even millenia before we had the tools to actually examine these things. And, now that we can, they are still among the hardest things to understand that humans have ever grappled with. Chapter 7, “Twist and Route,” is about the molecular machinery of movement and muscle: the motor proteins kinesin, myosin, and dynein. “There is not one type of kinesin, myosin, or dynein doing one type of job. Instead, like a fleet of customizable trucks, there are superfamilies of molecular motors, with eighteen known classes of myosins, ten classes of kinesins, and two classes of dyneins.” This rabbit hole goes deep. BACK TO TEXT
  3. Hessel AL, Lindstedt SL, Nishikawa KC. Physiological Mechanisms of Eccentric Contraction and Its Applications: A Role for the Giant Titin Protein. Front Physiol. 2017;8:70. PubMed #28232805. PainSci #53120.

    Shortly after the sliding filament theory of muscle contraction was introduced, there was a reluctant recognition that muscle behaved as if it contained an elastic filament. … This additional filament, the giant titin protein, was identified several decades later, and its roles in muscle contraction are still being discovered. Recent research has demonstrated that, like activation of thin filaments by calcium, titin is also activated in muscle sarcomeres by mechanisms only now being elucidated. … Titin stiffness appears to increase with muscle force production, providing a mechanism that explains two fundamental properties of eccentric contractions: their high force and low energetic cost.

    BACK TO TEXT
  4. Hessel et al: “The high force and low energy cost of eccentric contractions makes them particularly well suited for athletic training and rehabilitation. Eccentric exercise is commonly prescribed for treatment of a variety of conditions including sarcopenia, osteoporosis, and tendinosis.” BACK TO TEXT
  5. Frizziero A, Vittadini F, Fusco A, Giombini A, Masiero S. Efficacy of eccentric exercise in lower limb tendinopathies in athletes. J Sports Med Phys Fitness. 2016 Nov;56(11):1352–1358. PubMed #26609968. “Eccentric exercise (EE) is considered a fundamental therapeutic resource, especially for the treatment of Achilles and patellar tendinopathies.” BACK TO TEXT
  6. Mizumura K, Taguchi T. Delayed onset muscle soreness: Involvement of neurotrophic factors. J Physiol Sci. 2016 Jan;66(1):43–52. PubMed #26467448.

    A series of Japanese studies since 2010 have showed that the pain may be related to neurotrophic factors: substances secreted by muscles cells that goose nerve growth. A simpler way to say this would just be nerve growing pains. Exercise develops our nerves, and that’s uncomfortable.

    BACK TO TEXT
  7. Schaefer LV, Bittmann FN. Are there two forms of isometric muscle action? Results of the experimental study support a distinction between a holding and a pushing isometric muscle function. BMC Sports Sci Med Rehabil. 2017;9:11. PubMed #28503309. PainSci #52864. BACK TO TEXT