Laura Cwiklinski                                                                   January 2002

                                     Portfolio Piece

                                 Muscle Fibre Types

   There are three different types of muscle fibre found within the body. Each has a specific set of characteristics that determine the type of activity that a person will be much more able and capable of performing.


   The three types of muscle found within the body are:

                 -Slow oxidative fibres (SO)

            -Fast oxidative glycolytic fibres (FOG)

            -Fast glycolytic fibres (FG)

   Every muscle contains all three types but not in equal proportions. You will only find one fibre in any one given motor unit.

Type 1: Slow Oxidative Fibres

     The nerve impulse travels slowly to the muscle fibre because the myelin sheath is thin. Slow twitch fibres do not produce as much force as fast twitch fibres. They can however, have high levels of endurance. Slow twitch fibres are far more suited to aerobic work. They contain mitochondria and myoglobin, and have lots of blood capillaries. They have necessary enzymes to help break down fat and carbohydrate to carbon dioxide and water. It is a slower process than releasing energy anaerobically but it doesn’t produce any fatiguing by-products.

Type 2: Fast Oxidative Glycolytic Fibres.  

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     The motor neurone stimulating this fibre has a thicker myelin sheath than the slow twitch fibre, so it can contract more quickly and exert more force. There are lots of muscle fibres in each motor unit. This fibre type can produce energy both aerobically and anaerobically by the breakdown of carbohydrates to pyruvic acid, but it is more suited to anaerobic respiration, which means that energy can be released very quickly. There is a rapid build up of Lactic acid, which lowers the pH, and has a negative effect on enzyme action, causing the muscle fibre to fatigue ...

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