Slow Twitch vs. Fast Twitch Muscle Fibers

Every living animal on this planet has muscle fibers. There are some animals who can move for long distances like birds migrating through different seasons and there are some animals that can be very fast and explosive like a lion. That’s the same with human beings, some human beings are very good at long distance sports while some are 100m speedsters. This is because there are two types of muscle fibers in our body; slow and fast twitch fibers. They serve very different purposes.


Slow twitch fibers, also known as Type I muscle fibers, are muscle fibers that contract slowly. Due to the slow contraction, they do not generate a lot of power. Slow twitch fibers are a lot more efficient at using energy and due to that, they are fatigue resistance. This is because these fibers tend to be a lot smaller and are surrounded by capillaries. Many capillaries surround them, so they support aerobic metabolism as there will be more oxygen supply. This results in muscles that can work for a longer period of time with less energy output. This type of muscle fiber is most ideal for people who do long distance or stamina based sports such as marathons and triathlons. They grow through similar types of training over a period of time.


There are two types of fast twitch muscle fibers; moderate (Type IIA) and intense (TypeIIB). Type IIB being the larger one. However, both these fibers are larger in comparison to the Type I slow twitch fibers. Due to the larger size, they are able to produce more force however they need more oxygen to sustain them. Unfortunately, these large twitch muscle fibers are not surrounded by as many capillaries as the slow twitch fiber which makes them easier to fatigue. These muscle fibers are more effective for people who often do more explosive movements such as sprinters, weight lifters and jumpers. These muscles grow through resistance training.


What’s very interesting is even though if the sport demands mostly slow twitch fibers, small amounts fast twitch fibers are also recruited. This is because in the action of each movement a small amount of explosive strength comes out. In sports that require plenty of fast twitch fiber, once the primary fiber fatigues, your body will naturally push the small twitch fiber to do carry on the job. This is why it is important to train both types of muscle fibers.


The amount of fast twitch and slow twitch fiber is predetermined by genetics and at a young age. However, it is not said that they cannot be changed. Many of this is determined by the amount and type of training done. That being said changing between the two types of fast twitch fiber and from fast twitch to slow twitch can be achieved with much more ease compared to altering from slow to fast twitch fiber. However, this does not mean it cannot be done. As long as hard work reigns supreme, and by being consistent with the type of training.


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