Fast twitch fibres

Understanding the 2 different forms of fast twitch and how they function is key to getting the most of these muscles.

There are actually two different types of fast twitch muscle fibres, and though both share some commonalities, there are also clear differences between them.

The two types of fast twitch muscle fibres are:

  • Type 2A also known as fast oxidative-glycolytic
  • Type 2B or fast glycolytic

Type 2A, or fast oxidative-glycolytic,

They have a quick contraction speed. They are progressively recruited when we require an additional effort, but are nonetheless very resistant to fatigue.

Type 2A are used for aerobic metabolism, and are able to use either glucose or fats as a source of energy. Although they are general purpose muscle types, they have a higher energy cost than Type 1.

Type 2B, or fast glycolytic,

They have a quick contraction speed and are only recruited for brief maximal efforts they are easily fatigued. Because they have a poor surface to volume ratio, the delivery of oxygen and removal of waste products is limited they have a high energy cost, and are very quickly depleted.

They are what most people would think of as sprinters muscle fibres, and are therefore of no use for sustained performance.

Research shows that systematic training will change the balance of these different types within our bodies, allowing athletes to train themselves for the specific demands of their chosen event.

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