full article 700 words
When you think of a muscle contraction, you think of a muscle getting shorter, which is called “concentric” contraction — but that’s not always what happens. In fact, your muscles routinely have to pull off a trick known as “eccentric” contraction, and it is odd: contraction while lengthening, also sometimes called a braking contraction.
|concentric contraction||=||contraction while shortening|
|eccentric contraction||=||contraction while lengthening?!|
How is this possible? How can that even be called a “contraction”?
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 dominant theory of muscle contraction — the sarcomere model — cannot quite explain it.
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.
Other than intellectual interest, this is why you should care about eccentric contractions: because they hurt more!
Anyone who has ever exercised knows about that nasty feeling you can get in your muscles. Usually it’s worst the day after, sometimes two days after. It feels like your muscles have been bruised inside and out. If it’s bad enough, it’s like you can feel individual molecules of air bashing into your skin. The muscle is weak and incredibly sensitive to contraction until you recover.If it’s bad enough, it’s like you can feel individual molecules of air bashing into your skin.
This phenomenon is called delayed onset muscle soreness (DOMS) … 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.
Although concentric contraction can also cause DOMS, eccentric contractions are much worse. And — again — no one knows why. In fact, no one really understands DOMS, either. There’s no cure for it except to get it over with! See Delayed Onset Muscle Soreness (DOMS): The biological mysteries of “muscle fever,” nature’s little tax on exercise
How’s that for “biological literacy”? Now you can amaze your friends, team-mates, and running buddies with your knowledge of eccentric contractions! At least until they ask how it works, that is…
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.
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