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Types of muscle fibres
Thursday, 21 October 2021
Look at the images
on the right.
Are all skeletal
muscles the same –
discuss with a
Key words: slow twitch, fast twitch, myoglobin
Learning outcomes:
Describe and explain the structural
differences between fast and slow twitch
muscle fibres
Determine the types of fibres mainly
present in certain animal muscle tissue.
Predict the type of sports a person
would be good at based on a muscle biopsy
Lets recap – what do we already
Types of fibres
• Skeletal muscles are made up of two
types of muscle fibres – slow twitch and
fast twitch.
• Different muscles have different
proportions of these fibres.
Task 1 (12 minutes): determining
characteristics of the fibres
• Using the information in the worksheets
around the room, produce a table
comparing fast and slow twitch muscle
• Extension: give one reason why fast
twitch are likely to tire quickly
Energy source
Type of activity
suited to
Found in
Fast twitch
Slow twitch
• What can you tell
me about these
athletes and their
muscles now?
Task 2: fast or slow twitch quiz?
• You will be given information about certain
animal muscles. Working with a partner,
determine whether the majority of the meat
would contain fast or slow twitch muscle.
Hint: different parts may have a different ratio
Justify your
• Chickens spend a lot of time roaming around or
standing. Their thigh and leg muscles are used
constantly. They rarely fly, and then only for
very short distances so their breast and wing
muscles aren´t used often. In contrast, wild
birds such as ducks fly a lot.
• Cattle spend a lot of time standing, and so
their muscles are constantly being used.
Therefore, beef has a fairly high concentration
of myoglobin.
• Pigs also can spend quite a bit of time standing
and roaming around. However, the animals used
for pork are young and small, their muscles are
less developed and do less work.
• Fish float in water and don't need constant
muscle energy to support their skeletons. They
do use fins and tail constantly for swimming.
“Give me a muscle biopsy and I´ll tell you
whether you should be a sprinter or a
marathon runner”
Use your knowledge of fast and slow
twitch muscles to explain this diagram
Exam Question
• Give three structural differences between
slow (Type I) and fast (Type IIb) muscle fibres.
• Suggest why successful sprinters have a
relatively high percentage of fast fibres in their
Check your answer!
• slow / red / tonic / type I, fibres
• a smaller diameter ;
• wider Z lines ;
• lower glycogen content ;
• more capillaries ;
• higher myoglobin content ;
• more mitochondria ;
• less sarcoplasmic reticulum ;
• [accept converse for fast /
white / twitch / type II, fibres]
• sprinters need fast muscle
contraction ;
fast fibres produce more
power at fast contraction
speeds ;
fast fibres produce more
force than slow fibres ;
fast fibres have higher
ATPase activity ;
fast fibres have large store of
creatine phosphate ;
as immediate energy source
/ for ATP production ;
even when oxygen is
insufficient for aerobic
respiration ;
Resources to print
Speed of contraction
• Fast twitch muscles contract very quickly,
producing rapid, intense contractions.
• Slow twitch muscles are specialised for a
slower, sustained contraction.
Where do you find them?
• Slow twitch muscles are used for
posture e.g. in the back
• Fast twitch muscles are for fast
movement such as in the eyes and legs.
Types of activities
• Fast twitch muscles are good for short bursts
of speed and power e.g. sprinting and weight
lifting. They tire quickly
• Slow twitch muscles are good for endurance
sports such as running long distances. They
are slow to tire.
• Energy is released slowly through aerobic
respiration in slow twitch. They have many
mitochondria and blood vessels supplying
• Fast twitch rely on anaerobic respiration using
glycogen. There are few mitochondria and
blood vessels.
Colour of fibres
• Slow twitch fibres are reddish in colour
because they are rich in myoglobin ( a red
coloured protein that stores oxygen).
• Fast twitch fibres are whitish in colour
because they don´t have much myoglobin.
They respire anaerobically.
Glycogen and Creatine phosphate
• Slow twitch have low glycogen content and
low levels of creatine phosphate, (an
organic compound that provides a quick
source of energy for muscle fibers to
• Fast twitch muscle fibres have high levels
of both.