You’ve seen this talked about fast-twitch, slow-twitch, muscle fibers, mitochondria; what the heck are we talking about? Well, I’m Jesse Funk and on today’s episode of Runner’s High, we’re gonna figure out what the difference between fast-twitch and slow-twitch muscle fibers actually is.

Whether you watch running or you have just been a runner for a long time, somebody somewhere has certainly said fast-twitch, slow-twitch, oh, you need more of those slow-twitch muscle fibers. Those guys just have fast-twitch, all that kind of stuff. But what the heck are they actually talking about? Well, when we’re talking about muscle fibers, they come in these two basic forms; fast-twitch and slow-twitch.

As endurance athletes, runners, triathletes, whatever it is that you do, generally we want to rely on slow-twitch which is what you’ve probably heard. Those sprinters, they have all those fast-twitch, they go fast they go, you know, they’re really powerful.

Those generalizations really give us the basics of what the differences are. Fast-twitch are going to be the muscle fibers in our bodies that allow those explosive fast movements. They also fatigue quicker than slow-twitch. Those slow-twitch muscle fibers allow us to do those aerobic activities for a much, much longer period of time, and activate at those kind of levels. Now another important difference between fast-twitch and slow-twitch is that slow-twitch muscle fibers have a larger amount of mitochondria.

Now you’re like what the heck is mitochondria? Mitochondria are the powerhouse of the cell. That’s what produces energy. Now, I won’t go take you back to high school biology, we can talk about ATP and the Krebs cycle and all those kinds of things. But we can save that for another video. The important part to remember is that slow-twitch has more mitochondria, meaning it produces more energy and fatigues slower like I mentioned in the beginning.

The thing is that when the fast-twitch have less mitochondria, they fatigue faster, but they have a very useful, important purpose and that is high power.

If you see very, very large people, and I’m talking about bodybuilders, often not runners, they really worked on developing fast-twitch muscle fibers. Because if you want to gain bulk, you want to gain weight, you have to train fast-twitch. That’s another difference between them is that fast-twitch are larger and bulkier because they’re made for those forceful power functions. But what about the mix of these muscle fibers in our bodies?

Now, there is going to be some genetic components at play, obviously, because not all of us can be Olympians. But when we’re talking about somebody who’s say, non-athletic, which is probably not you because you’re here on this channel.

And if you are, subscribe, stick around for more running videos. But the non-athletic individuals typically could have a rough 50/50 spread of these fast-twitch versus slow-twitch muscle fibers. But when we begin to specialize like we do as runners or somebody who is a sprinter, or like a powerlifter or somebody like that, then you can see as high as 70 to 80% in one direction or the other.

With the powerlifters, that’s going to be the fast-twitch, for us as runners, that’s going to be the slow-twitch. It’s that specialization and working on a particular muscle type because of your activity, running or power lifting that helps those things develop and kind of skew in one direction or the other. The other thing is that age affects us as well as we get older, we get leaner, and we lose more of those fast-twitch muscle fibers, they become less prominent.

But we can also gain more of these slow-twitch muscle fibers which, and this is conjecture on my part. I don’t have enough research but thinking about that idea, it makes some sense, right? We know that endurance athletes typically peak, mid 30s give or take five years could be early 30s, late 30s.

But with that aging process if you’re able to gain slow-twitch muscle fibers, and runners and endurance athletes need those to be at the peak of their game, then it makes sense that aging is beneficial for them versus say a sprinter or a football player or a power athlete who are typically going to be younger.

It’s also in endurance sports when you see milers, even 5K, they’re going to be younger athletes most of the time when you’re talking about the best of the field. Versus marathoners, half marathon, half Ironman, Ironman, those kinds of events, obviously going to be those older athletes more typically.

So, if you’re coming to running, and you’re wondering, do I have enough slow-twitch muscle fibers to be good? Do I need to get rid of my fast-twitch? Do I need to do this or that? Really, the thing is, don’t worry about it. We talked about the differences, and know that training can help you specialize in running if that’s what you want to do. Now, your genetic potential is something entirely different. It is affected by those muscle fibers but also by other factors.

So, if you enjoy running, don’t worry about it. Let it go. Forget about it. You don’t really need to know about all the information we just talked about, even though you know it now because running is something you enjoy, right? And if you enjoy it, subscribe and hit that button. Stick around with me for more episodes, and I’ll see you next time on the next episode of Runner’s High.