1. MUSCULAR system Fibre Types
Learning Objectives
To be able to describe the characteristics of fast and slow twitch muscle fibre types (type I, type IIa and type Iix).
To be able to explain how their characteristics impact on their use in physical activities.
Content
1.1.10
Characteristics of fast and slow twitch muscle fibre types (type I, type IIa and type IIx) and how this impacts on their use in physical activities.
1.1.11
How the skeletal and muscular systems work together to allow participation in physical activity and sport.

2. Fibre Types Muscle Fibres can be fast twitch or slow twitch.
The proportion we have of each is genetically determined (inherited).
They both have advantages and disadvantages:
Having a high % of fast twitch fibres is advantageous in anaerobic activities, such as sprinting.
Having a high % of slow twitch fibres is advantageous in aerobic activities, such as endurance running/cycling/swimming.

3. Slow Twitch Fibres These are also known as Type I fibres.
They are efficient at using oxygen, but slower to contract so not as powerful.
They are efficient at using oxygen because they have:
Large amounts of myoglobin.
A large number of mitochondria.
A good capillary network.
These characteristics, which allow them to use oxygen efficiently, mean they are slow to fatigue.

4. Fast Twitch Fibres
Fast twitch fibres contract quickly, increasing the amount of force that can be exerted over a short time, but they are quick to fatigue.
There are 2 types of fast twitch fibres:
Type IIa
Thought to be a hybrid of type I and type IIx as they have the characteristics of both.
With appropriate training these fibre types can be adapted to become more like type I or type IIx fibres.
Type IIx
Fatigue quickly as they don’t have the myoglobin, mitochondria or capillary network of type I fibres.
They contract most quickly and produce the most power, so are particularly suited to activities requiring large amounts of force.

5. Place a range of activities / events along the spectrum according to which fibre type is best suited. In some activities you may want to place more than one at different points.

6. Questions
Explain why high numbers of capillaries in slow twitch muscle fibres is an advantage for endurance runners. (2 marks) Explain why a long distance runner would also benefit from some type IIx muscle fibres. (2 marks) Describe in detail how the skeletal and muscular system work together to perform a lay up in basketball. (6 marks)