Muscle Fiber Type: Did You Choose Your Sport or Did Your Sport Choose You?

Hey guys and welcome back! Or I suppose you should be welcoming me considering it has been nearly a YEAR since my previous (and first) blog post. Anyway, I’ve been thinking about more and more topics lately that I’d LOVE to spread some knowledge on so here goes..

Today’s topic of choice… MUSCLE FIBER TYPES. While performing power cleans this morning, I was reminded of how difficult they are for me. While I absolutely hate the “excuse” of genetics, many people don’t realize how much their genetic make up really DOES play a role in the type of athlete they are. While you can’t change your true fiber type, you CAN train to become more efficient at whatever it is you are trying to achieve.

Let’s start with some background info. Skeletal muscle has three fiber types; type I, type IIa, and type IIb. Each one has different properties that affect how they perform and how quickly they fatigue.

Type I Fibers are also known as “slow twitch” fibers. They have large amounts of myoglobin, oxygen, and mitochondria. Because of their oxygen rich quality, they are rather resistant to fatigue and therefore can perform “low level” loads for a more extended period of time. Thus, our postural muscles like the neck and spine are mostly comprised of type I fibers. On an athletic spectrum, marathon/distance runners have a great amount of type I fibers. Athletes that train and perform for endurance events like running, biking, and swimming are usually type I dominant.

Then we have Type IIa Fibers, which are known as “fast oxidative" fibers. While we haven’t reached Type IIb just yet, know that type IIa’s are a hybrid of type I and type II fibers. They do contain a large number of myoglobin and mitochondria like type I’s but they use BOTH aerobic and anaerobic metabolic cycles to manufacture ATP at a faster rate. Type I’s on the other hand, only use an aerobic metabolic cycle. Am I getting to “wordy” yet? Let me put it this way. Type IIa fibers (the hybrid) are able to produce strong and fast muscle contractions BUT are more prone to fatigue than the long lasting type I fibers.

Lastly, Type IIb Fibers are known as “fast glycolytic" fibers. These fibers contain much fewer mitochondria and lower levels of myoglobin, thus resulting in less oxygen. These fibers produce ATP slowly but break it down rather quickly. (WHAT DOES THAT EVEN MEAN JOELLE?) It means these fibers make for very short but fast bursts of power. Think of a sprinter for example. Quick bursts of power, but it results in rapid fatigue. A sprinter can exert immense power, but they could not hold that pace for an extended period of time. A large amount of type IIb fibers are found in the arms and legs.

NOTE: Most skeletal muscles contain a combination of all THREE types of muscle fibers. However, the proportions of the different fiber types that form specific muscles will vary based on ho the muscle is used and what you were genetically born with.

This leads me to my next question… did you choose your sport…or did your sport choose you? For example, I have always wanted to play and engage in power/strength-based sports. I did gymnastics, soccer, dance, and played lacrosse growing up. I’ve lifted weights, I’ve done power lifting, bodybuilding, etc. Yet, what am I best at? RUNNING. Yes, that’s right. I’m one of those sick people that running comes fairly easy to. Once I discovered this (rather my PE teachers), I quit my other power/contact sports (in middle school and high school) and became a cross-country runner. It came so naturally to me and was the only sport I was ever truly “skilled” at without trying much.

Now years later, I no longer identify myself as a runner. I used to enjoy it because I was good at it but I certainly don’t enjoy it the way I enjoy lifting weights now. Don’t get me wrong, I love me some good ol’ cardio now and again, but my training these passed few years has consisted of strength and hypertrophy based work, rather than endurance.

So, are you an athlete based on what you train or based on you proportion of muscle fibers? I suppose technically I’m an endurance athlete (genetically) however I train like a strength athlete because that’s what I prefer.

Strength and power athletes (sprinters, Olympic lifters, etc) tend to display a larger proportion of type IIa fibers while endurance athletes tend to display a larger proportion of type I muscle fibers.

While your training may play a role in causing your fiber types to shift (mixed evidence), there is a large genetic component in the determination of your fiber type. For instance, the lower body tends to display more type I muscle fibers than the upper body (think about how long our legs can carry us around for without getting tired).

While there is no easy way to know your fiber type breakdown, think about what kinds of sports or activities always came naturally to you. Do you gain strength easily? Do you have a lot of power or speed? Or do you do better exercising at lower intensities for longer periods of time? Now, according to several studies out there, its fairly unclear whether type I and type II fibers respond better or worse to different types of training. While there isn’t much conclusive evidence on planning your training around your muscle fiber types, you WILL get better at exercises and sports that your consistently practice. While power cleans are by no means easy for me, the more I do them, the stronger I get. Always remember that your fitness levels are exercise and sport specific, regardless of fiber type. In other words, if I want to get better at pull-ups, I need to actually DO pull-ups. You CAN improve your sprinting or other explosive movements (even if you are type I dominant), just know it's not necessarily because you are converting your muscle fiber types, rather, you’re training your body to become BETTER at that activity.

And, here’s a chart I made to sum it all up! *Note there are many other factors here; capillary density, oxidative capacity, size of the motor neuron, major storage fuel, etc, however I’m trying to keep this post somewhat easy to follow. If you have more questions or want to learn about this topic more in depth, I can point you to some references!

I hope you enjoyed the post! Please let me know your thoughts and feel free to make blog post requests! You can leave a comment on the main "blog" tab!! Thanks for reading!!!

Stay healthy,

Be happy,

Joelle Samantha

​© 2016 by Joelle Samantha Fitness, Inc.

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