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Muscle fibres used in sprinting and endurance races.

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Introduction

Muscle fibres used in sprinting and endurance races. Most skeletal muscles of the body are a mixture of all three types of skeletal muscle fibres, but their proportion varies depending on the usual action of the muscle. For example, postural muscles of the neck, back, and leg have a higher proportion of type I fibres. Muscles of the shoulders and arms are not constantly active but are used intermittently, usually for short periods of time, to produce large amounts of tension such as in lifting and throwing. These muscles have a higher proportion of type I and type II B fibres. Even though most skeletal muscle are a mixture of all three types of skeletal, all the skeletal muscle fibres of any one motor unit are all the same. In addition, the different skeletal muscle fibres in a muscle may be used in various ways, depending on need. For example, if only a weak contraction is needed to perform a task, only type I fibres are activated by their motor units. If a stronger contraction is needed, the motor units of type II A fibres are activated. ...read more.

Middle

creating even more power and speed, a sprinter will use these fibres at the start of the race to power out of the blocks. Type 11b muscle fibres are very quick to contract and can exert a large amont of force. They rely heavily on anaerobic repiration for releasing energy as they have very few mitochondria. This means energy is rapidly released but also that the muscle fibre type are large and this increases the contractile speed. The neurone also activates a greater number of muscle fibres meaning that each motor unit can produce much more force than slow oxidative motor units. Although because of there rapid fatiguing characteristics they are not able to be used for the full 100 meters distance and the type 11a fibres take over. The 5000m run. Just like in the one hundred meter sprint, the athlete taking part in the 5km run will use the type 11b and 11a muscle fibres right at the start of the race to get a quick start and try and get away from the pack of other competing athletes and also to put in a sprint finish for the line, however as was said above these fibres fatigue quickly so the runner will need to use the type 1 slow oxidative fibres for the majority of the race. ...read more.

Conclusion

anaerobic Force production Low High Very High Mitochondrial density High High Low Capillary density High Intermediate Low Oxidative capacity High High Low Glycolytic capacity Low High High Major storage fuel Triglycerides CP, Glycogen A person who has more type 11 B and type 11 A fibres can simply run faster than someone with less 11 A and B fibres. Wilmore and Costill state that whn looking at a sprinter and a distance runner there is a noticible difference in slow twitch (Type 1 fibres) and fast twitch (Type 11 A and B fibres) Athlete Gender Muscle Percentage of Slow Twitch Percentage of Fast Twitch Sprint Runner Male Gastrocnemius 24 76 Distance Runner Male Gastrocnemius 79 21 Honeybourne J, Hill M, Moors H, (1996) Advanced Physical Education and Sport For A level Second Edition London: Nelson Thornes. Comparing sprint runners to distance runners, if you ran someone with 70% Type I fibers versus someone who had 70% Type II fibers in a sprint, the Type II predominant person would always win because the Type I person could not generate enough force quickly enough to stand a chance, however over a longer distance the person with 70% Type 11 would fatigue and slow dramatically. ...read more.

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