If you’ve been watching the sprinting events during the track and field section of the London 2012 Olympic Games then at some stage you probably would have overheard the commentators making reference to fast twitch muscle fibres.

Many individuals often seem confused by this terminology and end up getting fast twitch and slow twitch muscle fibres confused and mixed up. This article aims to consider both fibre types and the fundamental differences between the two.

In actuality, there are three types of muscle fibre, not two and are classified as; slow twitch (type 1), type 2a and fast twitch (type 2b). Type 2a fibres can be considered and thought of as ‘in the middle’ fibres and have the ability to adopt traits of either type 1 or type 2b fibres dependant on the training they are exposed to. So far so good? Let us know move on to the fundamental differences between the fast twitch and slow twitch fibres;

Fundamental Differences
Ability To Produce Force

Fast twitch muscle fibres are larger in diameter than their counterparts and have an enhanced ability to grow and develop. This enhanced cross sectional fibre size also offers advantages with force production, allowing for greater force development and distribution than slow twitch fibres. This makes fast twitch fibres much more suited for activities such as heavy weightlifting. Slow twitch fibres can be considered at the opposite end of the spectrum and are most suited to low force, long endurance events.

Primary Fuel Source

Fast twitch fibres utilise ATP as their preferred fuel source, which derives from glucose molecules. This is stored within the muscles themselves and allows intense contractions for up to a maximum period of 10 seconds. After this time and up to a period of 3 minutes, the fuel source switches to glycogen. In contrast, slow twitch fibres use a combination of glucose and fats for their energy supply. This is a much slower process and can be maintained with constant intensity for a continued time period.

Muscle Fibre Blood Supply

The blood supply to slow twitch fibres can be considered extremely efficient and offers a very good supply. This delivers oxygen to the working fibres, allowing them to work for extended periods of time without fatigue. Conversely, fast twitch fibres have an overall poor blood supply. As stated above, an efficient blood supply is required to deliver oxygen, so without this fast twitch fibres quickly become fatigued. Due to these differences slow twitch are also referred to as red whilst fast twitch are white.

Final Word

The fundamental differences between fast twitch and slow twitch muscle fibres are clear for all to see. Their variations can be thought of under the larger categories of chemical, structural and functional, of which there are many.

It is evident just from reading the above differences that the high force producing, quick fatiguing fast twitch fibres are required for activities such as heavy weightlifting and sprinting whilst the low force producing, slow fatiguing and rich blood supply slow twitch fibres are essential to marathon runners and tri-athletes. Which category do you predominantly fall into?