Fast twitch muscle fibre contractions are very quick and they provide speed and strength to an athlete, however, they do fatigue a lot faster compared to slow twitch fibres meaning they are more common in sprinters like Usain Bolt and other sports that require quick actions. Usain Bolt’s muscles need to have short, intense bursts of energy to enable him to be as quick as he can, therefore, fast twitch fibres will be more efficient than slow twitch fibres in his sport. These muscle fibres don’t have many mitochondria or myoglobin, therefore, not much oxygen or energy reaching the muscles. However, they aren’t really needed anyway as sprinters don’t needed a lot of oxygen/energy to go to their muscles as their sport only last for around 10 seconds, compared to long distances runners that could go on for hours meaning a lot of oxygen would be needed. The way sprinters get their energy for when they run is ATP and glycogen, they are their main energy stores. However, ATP sources can rapidly deplete, lactic acid is a byproduct of the breaking down of glycogen, therefore, fast-twitch fibres can only be active for a short space of time. The problem with fast twitch muscle fibres is that they become fatigued very easily, however, this isn’t much of a disadvantage as sprinters aren’t running for long so they don’t feel it. Finally, fast twitch fibres have a low amount of capillaries, this would be a disadvantage for marathon runners but not for sprinters. That is why these muscle fibres are more suited to fast paced sports.Fast twitch fibres are subdivided into two types:Type 2aType 2a fibres are fast-contracting and able to produce a great force, but are also resistant to fatigue. These fibres have many myoglobin, a lot of mitochondria and a high density of capillaries. Type 2a fibres are red, they are able to generate a lot of ATP by processes called oxidative metabolic processes. ATP can be split at a high rate, they have very fast contractions and are resistant to becoming fatigued. These fibres are suited to middle-distance events. Type 2b Type 2b fibres contract rapidly and have the capacity to produce large amounts of force, but they fatigue faster, making them better suited to anaerobic activities. These fibres don’t have a lot of myoglobin, mitochondria or capillaries compared to type 2b. Type 2b fibres are white, they aren’t able to continuously supply skeletal muscle fibres with the needed amounts of ATP, they fatigue easily, split ATP at a rapid rate and have fast contractions. They depend on anaerobic metabolism and are recruited for short, intense sports.