MUSCLE FIBRE TYPES (DOC)

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					MUSCLE FIBRE TYPES and Their Properties

Without getting into the physiology behind muscle contraction just yet,
we will look at the muscle fibre types and their properties.

Basically if a stimulus is received by muscle cells (fibres) and it is great
enough to cause a response – the fibres respond by contracting &
relaxing (1st glimpse at “All or None principle”).

All muscle fibre types can operate at the same metabolic capabilities,
but some are better biochemically equipped to work anaerobically or
aerobically (without or with oxygen).

Anaerobic – activity of a high intensity that does not allow oxygen to be
used in the metabolic process of ATP breakdown (e.g. maximal effort
sprint 50m); if duration of activity of such an intensity continues, lactic
acid is produced and build-up leads to fatigue (e.g. maximal effort
200m sprint)

Aerobic – activity of a lower intensity in which oxygen is used in the
process of breaking down carbohydrates & fats for fuel source (e.g. 5
min + jogging)

We will discuss these energy systems in greater detail in the next unit,
however, it is important to recognize that different muscle fibre types
are related to each of these.

Slow-twitch fibres (ST)
 AEROBIC (with O2)

 Red in colour

 Type I (slow-oxidative)

 E.g. leg muscles



Fast-twitch (FT)
 ANAEROBIC (Without O2)

 White in colour

 Type IIa & IIb

 E.g. arm muscles
                    PROPERTIES OF MUSCLE FIBRES
                       TYPE I        TYPE IIa           TYPE IIb
    Speed of            Slow           Fast               Fast
   contraction
 Primary source
      of ATP
 Rate of fatigue
       # of
   mitochondria
Capillary density
     Glycogen
     capacity
 Fibre diameter
  Size of Motor
      Neuron
Force Production
    Oxidative
     Capacity
Activity used for

During the teen years, the number of ST and FT fibres become “fixed”;
training can elicit some change, but for the most part, # of specific
fibres & arrangement is pre-determined by genetics.
Complete the chart of fibre charateristics
www.brianmac.demon.co.uk/energy.htm
Characteristics and Properties of Muscle Fibres (Skeletal)
Compare the differences between muscle fibres. Which fibres would be
most dominant in which type of athletic activity.
                   PROPERTIES OF MUSCLE FIBRES
                       TYPE I            TYPE IIa          TYPE IIb
    Speed of
   contraction
 Primary source
     of ATP
 Rate of fatigue

       # of
  mitochondria
Capillary density

    Glycogen
    capacity
 Fibre diameter

 Size of Motor
    Neuron
Force Production

   Oxidative
    Capacity
Activity used for

   Conduction
     velocity
www.brianmac.demon.co.uk/energy.htm
Exercise Science: An Introduction to Health and Physical Education

				
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posted:11/22/2011
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