Protein ACTN3 in fast twitch muscle

Muscle Composition and ACTN3

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When I got my DNA test results back from 23andMe, one of the things it said made me laugh. It said I had muscle composition common in elite power athletes.

Here, let me show you:

Muscle Composition - from 23andme dna body type

When I first saw this result I thought it had to do with what types of muscles I had. We all have two types of muscles, fast twitch and slow twitch. Not surprisingly, fast twitch muscles are the ones we use when we are using bursts of energy, like in sprinting. Slow twitch muscles are the ones that we use when we do slower continuous movements, like long distance running. Makes sense, right? Now, we all have both. But, depending on your genetics and how you exercise you can have more of one kind or another. So, might be born with more slow twitch muscle fibers, but if all you practice is 200-meter sprints, you will develop more fast twitch muscles.

So, when I read this report I thought it was saying I was predisposed to having fast twitch muscles. That seemed ridiculous to me! For one thing, as I have mentioned, I am a “back-of-the-packer” when it comes to running. This is not only true in long runs, it is true in short ones too. I’m just slow. From my long distance running experience, my body starts feeling good about running somewhere around mile 6. (Yeah, this means 5Ks pretty much suck.) That leads me to believe that I am more of an endurance athlete. Hey, who says those DNA tests are perfect, right?

But then I started reading a chapter on aerobic and anaerobic metabolism in my Precision Nutrition Sports and Exercise Nutrition textbook and I found something interesting. It also talked about fast twitch and slow twitch muscle fiber types, and how different exercise types affect our bodies. The example they gave for fast twitch muscles and anaerobic exercise was CrossFit and Weightlifting, specifically in engaging your muscles quickly to do those quick movements or get under the bar. And hey, those are two things I do! I lift with The West Michigan Barbell Club and workout at CrossFit 616. Now, I am not going to say I am at the top of my class or anything, but every once and awhile my Coach or someone in class will compliment me for my speed on getting under that bar. It makes me wonder if it isn’t my body that is holding me back from being fast… it’s my brain.

Protein ACTN3 in fast twitch muscle
I love these illustrations of proteins on Wikipedia, they are just so cool! This one of ACTN3 is by Emw

So, I went back to 23andMe to learn more. I dug into it a little further and found this:

This report is based on a genetic marker in the ACTN3 gene. This marker controls whether muscle cells produce a protein (called alpha-actinin-3) that’s found in fast-twitch muscle fibers. 

(They didn’t link to the Wikipedia article, by the way, that was me because it has a ton of cool resource links on the bottom.) Anyway –

So, what is really happening here is that ACTN3 is a protein that is only generated by fast twitch muscles. And not everyone can do it, even with fast twitch muscles. It’s genetic. While it isn’t known for sure that this protein enhances performance, what they have found is that elite athletes all seem to have the ability to create this protein or one of its mutations. So basically, if I had become an athlete in my youth, it might have helped. My guess is that it isn’t the kind of thing that matters at all to regular folks but for a performance athlete, that tiny extra bit might gain them a tenth of a second and that is all they need.

So for me, it doesn’t mean much, but it’s still so fascinating to learn about. I am so interested in how the body works, how genetics and other factors affect it. We are such complex and extraordinary creatures!



Wikipedia – Actin alpha 3


Precision Nutrition

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