The Pain in the Gain: Delayed Onset Muscle Soreness

August 5, 2009

The sarcomere is the function unit of skeletal muscles (credit: Wikimedia)

The sarcomere is the functional unit of skeletal muscles (credit: Wikimedia)

I was out chopping wood yesterday (which, let me tell you, is incredibly good exercise) and today have distinct muscle soreness in my lower back. I’m sure most of you have experienced this post-exercise soreness at some point or another and so decided to learn what I could about what’s called Delayed Onset Muscle Soreness (DOMS). (Most of my information came from the this solid review of DOMS by Priscilla Clarkson.)

The functional unit of your skeletal muscle (as opposed to smooth muscle) is the sarcomere. Much of the damage that results with DOMS involves injury parts of the sarcomere. Specifically, the Z-lines and the protein that holds them together, desmin, are disrupted. As these individual muscle fibers are strained, the extracellular matrix (which is a scaffold for your cells and other proteins outside the cell, including muscle fibers) is pulled apart from the fibers. Furthermore, there’s evidence that small capillaries are broken in this process as well which also help to trigger an inflammation response by your body.

One of the hallmarks of muscle injury and its subsequent DOMS is a loss of strength in that muscle. The most prevalent explanation for this loss is what’s know as the “popping sarcomere hypothesis,” which posits that the irregular lengthening of individual sarcomeres (that is, some get stretched out a lot, others not as much, rather than all of them an equal amount) causes the muscle fiber to be weaker (since the overlap between the thick myosin and thin actin filaments is less in a stretched-out sarcomere).

Finally, what causes that thing we care most about: the soreness? It comes in part from the tissue swelling and and fluid pressure in the muscle. (For those of you who doubt swelling hurts, I can tell that my forearm, which is the size of Popeye’s thanks to a wasp sting yesterday, hurts a good deal even though the pain of the sting is gone.) It’s also suspected (although not distinctly proven) that the pain also comes from the release of molecules (histamines, bradykinins, and postagladins) from damaged cells that active the type III and IV afferent nerves, which basically carry pain signals to the brain.

So the next time you feel that soreness the day after some hard working out, think of your out of wack Z-links and painful histamines but know that your body’s smart enough to replace that damaged muscle with more so you won’t have the same reaction a second time (unless, of course, you damage it more).

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