If you’re a 10k runner you rely on more explosive muscle fiber and therefore have predominantly fast twitch muscle fiber.

Let’s dive into the first of the 2 basic principles of endurance sports in general and ultra running in particular. The different types of muscle fiber.

Our body has 2 different types of muscle fiber

and 3 different energy systems. These are linked, but more on the linkage in the next post, now it’s time to fiber things up in the muscles.

The types of muscle fiber are slow twitch muscle fiber and fast twitch muscle fiber.

Fast twitch muscle fiber

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If you’re a 10k runner you rely on more explosive muscle fiber and therefore have predominantly fast twitch muscle fiber. Shorter high intensity efforts builds this type of muscle fiber. It’s fast and explosive but tires quickly.

Slow twitch muscle fiber

If you do longer distance races like marathon and beyond chances are you have predominantly slow twitch muscle fiber. Slow twitch muscle fiber are not that explosive but have much better endurance and does not tire so quickly as fast twitch muscle fiber.

So what does this mean for my ultra running carrer?

This means that you need to do training that will train you proper muscle fiber to be able to go long.

Now on to the energy systems in the next part.