Type 11a fast oxidative glycolytic fibers has a thick myelin shealth, this allows it to contract quicker and exert more force than the type 1 slow oxidative fibres. The amount of force produced by the type 11a fibre is greater than type 1 fibre because there are more muscle fibres in each motor unit. This fibre tpecan produce energy both aerobically and anaerobically by breaking down carbohydrate to pyruvic acid but it is much more suited to anaerobic respiration, which mean it can release energy very quickly.
This is ideal for a 100 meter sprinter who needs to be able to produce maximal muscular exertion within those 10 seconds of sprinting, however the rapid build up of lactic acid which is a by product of anaerobic respiration dramatically lowers pH and has a negative affect on enzyme action, causing the muscular fibre to fatigue quickly. This means that if the sprinter were to try and carry on sprinting past the 100 meters distance, he would not be exerting the same power from the muscle contraction and would also be beguining to tire rapidly.
Although the type 11a fibres are able to produce maximal contraction there is another fibre know as the type 11b fast glycolytic fibres which can contract even quicker, 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.
Type 1 slow oxidative fibres ar also know as slow twitch fibres becase they contract more slowly than type 11 (fast twitch) fibres. The myelin sheath of the motor neurone stimulating the muscle fibre is not as thick as that of the fast twitch unit, and this reduces the amount of insulation, slowing down the nerve impulse. Slow twitch fibres do not produce as much force as fast twitch fibres but can easily cope with prolonged bouts of exercise, this means that the 5000m runner can maintain a speed that is not quite maximal for a long period of time.
They are more suited to aerobic work as they contain more mitochondria and myoglobin and have more blood capillaries than fast twitch fibres. Slow twitch fibres have enzymes necessary for aerobic repiration and are able to break down fat and carbohydrate to carbon dioxide and water. This is a slower process than releasing energy anaerobically but it does not produce any fatiguing by products, again this enables the runner to keep going with out getting overwhelming muscle fatigue, and the muscle beguining to ‘cramp up.’Type 1 fibres are slightly useless for sprininting though. However, they are certaininly recruited during sprinting. It s just that they are incapable of generating enough force quickly enough to be used solely for sprinting. Type 1 fibres are just not quick enough to generate maximal force.
The table shows the Characteristics of the different muscle fibres
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)
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.
References From
Honeybourne J, Hill M, Moors H, (1996) Advanced Physical Education and Sport For A level Second Edition London: Nelson Thornes.
Bibliography
Baker M, Indge B and Rowland M, (2001) Further studies in Biology
London: Hodder and Stoughton
Structures of skeletal muscle (Accessed 28th November 2003)
Westerblad, H., Lee, J. A., Lännergren, J., & Allen, D. G. (1991). Cellular mechanisms of fatigue in skeletal muscle. American Journal of Physiology
