Muscle Fibres
Learning Outcomes
 All are able to apply
knowledge of the fibres to
sporting events
 Most are able to explain the
role of the motor unit in
contraction.
 Some are able to apply
knowledge to a range of
sporting activities.
Homework
 Write up a neat copy of your extended
question to be marked
 Prepare for Mock exam – Tues 7th
October
 Bring in file with all Muscle Notes
Starter Activity
Question chain activity to recap muscle
fibres.
Complete exam question
 The motor unit is the basic functional unit of skeletal
muscle.
 The motor unit is the motor nerve (neurone) and the group
of muscle fibres that it controls.
Motor unit
 Stimulation of one motor neuron causes all the muscle
fibres in that motor unit to contract simultaneously.
 Each muscle is made up of a number of units. The number
recruited varies depending on strength required.
 Number of fibres within a motor unit is dependent on
control required.
 Small muscle for fine motor skill may only require one
fibre per motor unit e.g. eye to focus
 Large muscle for gross skill may need 500 or more
fibres e.g. kicking a football
Motor unit
 Motor units are usually made up of the
same muscle fibre.
 So we see both fast and slow twitch
motor units in a muscle.
All or none law
 The innervation (stimulation) of a muscle occurs
when a motor neuron transmits a nerve impulse
to the muscle fibre.
 The all or none law states that if a motor impulse
is of sufficient intensity, the motor unit is
stimulated and all the muscle fibres within it will
contract to their maximum potential.
 Either the neurone will fire a response or it won't.
There is no partial response.
Graduation of contraction
 Give handout – diagrams
 The force exerted by a muscle is dependent on:
 Recruitment: the more motor units recruited, the more
muscle fibres that contract, thus increasing the force
produced.
 Frequency: decreasing the time between impulses so
that the muscle fibres do not have time to relax,
resulting in a continuous wave of contractions known as
wave summation.
Graduation of contraction
 Timing: spatial summation – To create a greater force of
contraction the brain recruits more and larger motor units.
 Use bigger/larger motor units
 More motor units
 More and larger units leads to increased strength/more force in
muscles
 FT units produce more force than ST units.
Effect of training
 Resistance training will result in some long term
physiological responses to the neuromuscular system:
 Recruitment of more motor units (trained to act
together)
 Muscle hypertrophy (due to increases in size of fibres or
hyperplasia – splitting of fibres)
 Conversion of type 2b to type 2a (delays fatigue in
prolonged training).
Plenary Activity
 Individually explain how the strength of muscle
contraction can be varied in relation to a high jumper
and a distance runner.
 Share this information with a partner between you
come up with an agreed answer.
 Be prepared to share this information
Plenary activity
The strength of a muscle contraction can be increased
 Use bigger/larger motor units
 More motor units
 More and larger units leads to increased strength/more force
in muscles
 FT units produce more force than ST units.
 All or none law
 If all motor units are stimulated at same time then max force can be
applied
 High jumper – predominantly FT muscle fibres
 Marathon runner – predominantly ST muscle fibres
Exam Q
 Complete this question in pairs:
 How can a performer vary the strength of muscular
contractions to ensure that a skill is completed
correctly? (4 marks)
A. (Greater the force needed) larger motor units recruited
B. More units recruited
C. Need fast twitch fibres rather than slow twitch fibres
D. Multiple unit summation/spatial summation
E. All or none law/All or nothing law/or explanation
F. Wave summation/frequency of impulse/innervations
G. Motor unit unable to relax/increase the force
H. Tetanus/titanic for powerful contraction
I. Muscle spindles detect changes in muscle length/speed of contraction
J. Send information to brain/CNS
K. Compares information to long term memory to ensure correct force applied/past
experiences
L. Spatial summation – rotating the frequency of the impulse to motor units to delay
fatigue
Extended question
 In pairs use your notes to complete a draft version of
the extended question.