Muscle Fibers Explained: Type 1 and Type 2

Most people aren’t aware that the muscle fibers in their body aren’t all the same, but are very different from one another in that they are evolved to work in very different ways. Commonly they are separated into two groups – aptly named Type 1 fibers and Type 2 fibers.

Let me explain to you a little about each.

Type 1 fibers:

These are red fibers, and are sometimes known as oxidative fibers due to the fact they produce ATP (muscle energy) through intake of oxygen. Type 1 fibers are slow twitch fibers, which are built for slow but enduring movement because they are able to refuel by taking in oxygen when a person draws breath.

A person running a marathon, for instance, will be using Type 1 fibers.

Type 2 fibers:

Now, the article title may have misled you a little – because Type 2 fibers actually contain 2 subgroups: Type 2a and Type 2b.

Type 2a fibers:

Type 2a fibers are what you might call the middle ground between Type 1 and Type 2b fibers (which is a hint to what they are). They are red fibers, and can also generate ATP from a person breathing oxygen. These fibers are able to ‘burn energy’ at a higher more explosive rate, and while this makes these muscles more explosive, it also makes them quicker to fatigue than Type 1 fibers.

Someone running an 800 – 12000 metre race would for instance be using Type 2a fibers.

Type 2b fibers:

Type 2b fibers are the complete antithesis of Type 1 fibers. They are white fibers, and hold very little capacity for endurance. They are the most explosive muscle fibers in the body, and are used for events such as sprinting, long jump, high jump, shot put, hammer throwing, power lifting, and Olympic weight lifting… basically any event that requires a massive one-off or very unsustainable effort. The force generated is huge, and as such, the energy burned and muscle fibers fatigued quickly.


The muscles of the body therefore are evolved to allow the maximum recruitment of the specific types of fibers to match the effort needed. That’s why training with weights in the manner needed to target the specific types of fibers will only work to strengthen and build the muscle types being targeted. For instance, hitting Type 2b fibers will do nothing for Type 1 endurance fibers, and vice versa.

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