Transcript Types of Muscle Fibre

Types of Muscle Fibre
Learning Objectives:
1. To know the structural and functional differences
between different types of muscle fibre.
2. To know how muscle fibre type affects sporting
performance.
3. To understand the function of motor units in
muscle contraction.
Muscle Fibre Revision
Team 1 – Gary, Luke, Alex.
Team 2 – Callum, Matty.
Team 3 – Michael, Archie, Rich.
Team 4 - James, Dan.
Give two structural and two functional characteristics of slow
twitch fibres.
2. Fast twitch fibres are able to contract more quickly. Explain why
this is.
3. Fast twitch fibres are able to contract more powerfully. Explain
why this is.
4. Explain why slow twitch fibres do not fatigue as easily as fast
twitch fibres.




1.
Characteristics of
Muscle Fibres
Slow twitch fibres
Fast oxidative
glycotic fibres
Fast glycotic fibres
Fibres per motor
neurone
10-180
300-800
300-800
Motor neurone size
small
large
large
Type of Myosin
ATPase
slow
fast
fast
Sarcoplasmic
reticulum
development
low
high
high
Aerobic capacity
high
moderate
low
Anaerobic capacity
low
high
very high
Contractile speed
slow
fast
fast
Fatigue resistance
high
moderate
low
Motor unit strength
low
high
high
Structural
Functional
Muscle Fibre Percentages
Athlete
Muscle
% Slow twitch
% Fast twitch
Sprinter
Gastrocnemius
25
75
Marathon runner
Gastrocnemius
75
25
Swimmer
Deltoid
67
33
Shot-Putter
Gastrocnemius
38
62
Non-athlete
Quadriceps
47
53
Sporting Performance
- Slow twitch fibres suit endurance athletes.
- Fast twitch fibres suit sprint activities.
- An individual with a high percentage of fast twitch fibres
therefore has a natural advantage.
- However, other factors play a key role, as the table below
shows.
Range of % slow twitch
fibres
Average % slow twitch
fibres
Marathon Runners
50-95
85
800m Runners
50-80
55
Sprinters
20-55
35
Responses to Training
 % of fast/slow twitch muscle fibres is genetically

•
•
•
•
determined.
endurance training results in type IIb being converted to type
IIa.
explains why long steady training results in loss of speed.
endurance training increases the aerobic capacity of ST
fibres.
high intensity anaerobic training causes increase in size of FT
fibres (hypertrophy), and number of FT fibres (hyperplasia).
lack of training causes atrophy.
Motor Units
 A motor unit consists of a motor neurone and all of the fibres that are supplied by that






motor unit
A neurone does not activate a single muscle fibre, but a group of muscle fibres (the ‘all
or none law’)
All the muscle fibres in a motor unit will be the same type (Type IIa)
Therefore it is more accurate to talk of fast and slow twitch motor units rather than
muscle fibres
The number of muscle fibres supplied by a neurone in a motor unit dependent on the
degree of control required by the muscle.
In muscles that require a high degree of fine control there may be as few as 5 muscle
fibres supplied by the neurone e.g. eyelids
In large muscles that do not require a high degree of control there may be 1000 muscle
fibres supplied by a motor nerve in a motor unit e.g. the hamstrings
Spatial Summation
 The response of a motor unit follows the ‘all or nothing law’
 However, the strength of the response of the whole muscle is
determined by the number of motor units involved.
 For greater force the brain recruits more motor units.
 This is called spatial summation.
Muscle Fibre Exam Questions
1.
2.
3.
4.
5.
During a race, a swimmer has to dive off the starting
blocks as quickly as possible. Identify the ‘muscle fibre
type’ used to complete this action and justify your answer.
(3)
What are the main characteristics of the main type of
motor unit used in marathon running? (4)
How are motor units involved in spatial summation? (3)
What do you understand by the term motor units? (3)
The table below shows the percentage of slow twitch fibres
in elite sprinters. Discuss whether the sampling of muscle
is a good indicator of sprinting performance. (3)
Male Sprinters
Range of % of ST fibres
Avg % of ST fibres
20-55
35
During a race, a swimmer has to dive off the
starting blocks as quickly as possible. Identify the
‘muscle fibre type’ used to complete this action
and justify your answer. (3)
 Fast twitch fibres / type 2 fibres.
 Fast speed of contraction.
 High force of contraction / powerful contraction.
What are the main characteristics of the main type
of motor unit used in marathon running? (4)
 Slow twitch fibres.
 Contract less powerfully.
 Contract slowly.
 High fatigue resistance.
How are motor units involved in spatial summation? (3)
 Motor units follow the all or nothing law – all fibres within a
motor unit either contract or do not contract.
 The strength of contraction is determined by the number of
motor units recruited.
 To produce greater force of contraction more motor units
are recruited.
 For movements that require more fine control fewer motor
units are involved.
What do you understand by the term motor units?
(3)
 A motor unit consists of a motor neurone and all of the
fibres that are supplied by that motor unit
 A neurone does not activate a single muscle fibre, but a
group of muscle fibres (the ‘all or none law’)
 All the muscle fibres in a motor unit will be the same
type (Type IIa)
 The number of muscle fibres supplied by a neurone in a
motor unit dependent on the degree of control required
by the muscle.
The table below shows the percentage of slow twitch
fibres in elite sprinters. Discuss whether the sampling of
muscle is a good indicator of sprinting performance. (3)
Male Sprinters
Range of % of ST
fibres
Avg % of ST fibres
20-55
35
 A higher percentage of fast twitch fibres gives a natural
advantage for sprint events.
 However, this does not mean that an individual with a high
percentage of FT fibres will show good sprinting
performance.
 Other factors such as motivation, lever length, physique, VO2
max also play an important role.