Download Types of Muscle Fibre

A muscle fibre is a long
cylindrical muscle cell held
together in bundles to make up
an individual skeletal muscle
 Human skeletal muscles consist of a mixture of each
type of muscle fibre
 The relative proportion of each fibre type varies in the
same muscles of different people e.g. Elite marathon
runners have a greater proportion of slow twitch fibres
and elite sprinters have more fast twitch fibres.
 The two main types can be distinguished on the basis
of their speed of contractions
Slow Twitch Fibres (Type I)
 Slow twitch fibres are designed for aerobic exercise,
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using oxygen to produce a small amount of tension
over a long period of time
They are very resistant to fatigue as the speed of the
contraction is slow
They have a higher capacity for aerobic respiration
They are red in colour because of more myoglobin
Performers in endurance events tend to have a higher
percentage of slow twitch muscle fibres
Slow twitch muscle fibre composition of various athletes
Athletic group
Shoulder (Deltoid)
Long distance
runners
Calf
(Gastrocnemius)
79% (m), 69% (f)
Canoeists
71% (m)
Triathletes
60% (m)
Swimmers
67% (m), 69% (f)
Sprinters
59% (m)
Shot Putters
63% (m)
24% (m), 27% (f)
Cyclists
Weight Lifters
Thigh (Vastus
lateralis)
57% (m), 51% (f)
53% (m)
44% (m)
38% (m)
Fast Twitch Fibres – Type 2a and 2b
 Subdivided in to two types; Fast Oxidative Glycolytic
fibres (F.O.G.) and Fast Twitch Glycolytic (F.T.G.)
 They are both designed for anaerobic capacity,
producing high contractions in a short period of time
 This however means that they have a low resistance to
fatigue
 They are white in colour because of low levels of
myoglobin
Relative percentages of fast and slow twitch
fibres in a range of sporting activities
90
80
70
60
50
Type I Fibres
40
Type II Fibres
30
20
10
0
Fast Oxidative Glycolytic Fibres
(F.O.G.) – Type 2a
 These anaerobic fibres are more resistant to fatigue that
type 2b
 FOG fibres generate less force than type 2b fibres though
 Activities such as a 200m swim or 800m race will rely on
type 2a fibres.
Fast Twitch Gylcolytic (F.T.G) – Type 2b
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Type 2b fibres have the greatest anaerobic capacity
Generate largest amount of force of contraction
Very poor resistance to fatigue
Expect a Sprinter or Shot Putter to have large amounts of
FTG fibres
Summary of muscle fibre types
Characteristics
Slow Twitch (Type I)
Fast Oxidative
Glycolytic (Type
2a)
Fast Glycolytic
(Type 2b)
Fibre Size
Small
Large
Large
Mitochondria
density
High
Low
Lowest
No of capillaries
Large
Moderate
Small
Myoglobin content
High
Moderate
Low
PC stores
Low
High
High
Glycogen stores
Low
High
High
Triglyceride stores
High
Moderate
Low
Speed of contraction Slow (110)
(ms)
Fast (50)
Fastest (<50)
Force of contraction
Low
High
Highest
Resistance to fatigue
High
Low
Lowest
Aerobic capacity
High
Low
Lowest
Anaerobic capacity
Low
High
Highest
Activity suited to
Marathon
1500m
110m Hurdler
Past exam question
Anatomy and Physiology
Question 1
In terms of fibre type, the composition of muscle is largely
genetically determined and can influence the activities in
which people participate.
a.
Identify two structural and two functional characteristics of a
slow oxidative muscle fibre.
b. If a person has a high percentage of slow oxidative fibres
what type of physical activity are they more likely to participate
in? [5]