Are Muscle Fibre Types Genetically Determined Or Determined By Training?

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Introduction

Are Muscle Fibre Types Genetically Determined Or Determined By Training? The type of muscle fibres an athlete possesses will prove to be a limiting, or promoting factor in the sport an athlete chooses to participate in. There are two main types of muscle fibre, slow twitch and fast twitch. Slow twitch fibres enable an athlete to perform under aerobic conditions whilst fast twitch fibres enable an athlete to perform under anaerobic conditions. Therefore the percentage an athlete possesses of each can be a predictor of how well an athlete will do in a given sport. The percentage of each type of fibre an athlete possesses is genetically determined. That is it is inherent from parents and other ancestors. This could be shown by a muscle biopsy taken, for example (although not practical in real life), at birth and then again at a later stage in the athletes life. The percentage of muscle fibre types would still be the same.

Middle

They have a greater resistance to fatigue and higher aerobic capacity than type IIb. These muscle fibres can be utilised through training to give an enhanced performance. They can be changed through training. Although this does not change the percentage of genetically determined muscle fibre types in the body, it does show that training plays a part in our muscle fibre make up, and also shows that a person with high percentage of fast twitch fibres could still compete in a marathon against athletes with higher percentages of slow twitch fibres. Training is obviously an important factor to consider. Training causes changes to the body as a whole. For endurance training one of the main adaptations is increased VO2 max. This means more oxygen can reach the muscles and so they can work harder and longer. Endurance training also increases the number of capillaries around type I muscle fibres meaning they can get more oxygen to them.

Conclusion

After looking at both sides of the argument it is clear to see that neither is completely right. Our fibre types are indeed determined genetically and we will be stuck with what we were born with but it is not the only factor that needs to be considered. It has been shown here that through training of either type of muscle fibre it is possible to exploit our existing fibres to a better degree and that also with motivation to do well our genetically determined fibre types do not have to be a limiting factor. Unfortunately, so far, there has not been any 100% conclusive scientific evidence that can prove that muscle fibres do or do not change with training, as studies have not been conducted over long enough time periods. It is appropriate to say that the evidence so far shows that type I cannot be changed but type IIa can modify to being like type IIb and also more like type I fibres. Thus meaning we can always train to be what we wish to be. Elliott Owen: N0036961 Word Count: 841

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