Muscle Fibre Types and Movement Efficiency
Muscle fibre type plays a key role in determining how efficiently the body produces movement. In IB Sports, Exercise and Health Science (SEHS), muscle fibre types are used to explain differences in endurance, speed, strength, and fatigue between individuals and activities.
Understanding muscle fibre types helps students analyse why some athletes excel in endurance sports while others perform better in explosive or power-based events.
Overview of Muscle Fibre Types
Skeletal muscles are made up of different muscle fibre types, each with unique structural and functional characteristics. The two main fibre types studied in IB SEHS are:
- Slow-twitch fibres (Type I)
- Fast-twitch fibres (Type II)
The proportion of these fibres varies between individuals and influences movement efficiency and performance potential.
Slow-Twitch Muscle Fibres (Type I)
Slow-twitch fibres are specialised for endurance and efficiency over long durations.
Key characteristics include:
- High resistance to fatigue
- High aerobic capacity
- Lower force production
- Slower contraction speed
These fibres rely heavily on aerobic metabolism, making them efficient at producing energy over long periods. They are well suited to activities such as long-distance running or cycling.
In IB SEHS, slow-twitch fibres are linked to efficient, sustained movement rather than explosive power.
Fast-Twitch Muscle Fibres (Type II)
Fast-twitch fibres are adapted for high-force, high-speed movements.
Key characteristics include:
- Rapid contraction speed
- High force production
- Greater reliance on anaerobic metabolism
- Faster fatigue
Fast-twitch fibres are essential for activities requiring power and speed, such as sprinting, jumping, or throwing. However, they are less efficient over long durations due to rapid fatigue.
Muscle Fibre Types and Movement Efficiency
Movement efficiency depends on matching fibre type recruitment to activity demands. Endurance activities rely more on slow-twitch fibres, which use energy efficiently. Power-based movements rely more on fast-twitch fibres, which produce greater force but fatigue quickly.
Efficient performance occurs when the appropriate fibre types are recruited for the task being performed.
Training and Muscle Fibre Function
While fibre type distribution is largely genetic, training can improve the efficiency and performance of existing fibres. Endurance training enhances aerobic capacity, while resistance and sprint training improve fast-twitch fibre performance.
In IB SEHS, students should avoid claiming that fibre types can fully change, as this is a common misconception.
Exam Relevance for IB SEHS
Muscle fibre questions often require comparison and application. High-mark answers clearly describe characteristics of each fibre type and link them to specific movements or sports.
Avoid listing features without explaining how they affect performance or efficiency.
RevisionDojo Call to Action
If muscle fibre topics feel repetitive or confusing, RevisionDojo helps IB SEHS students master biomechanics with clear explanations and exam-style practice. It is the most effective way to build confidence in movement efficiency topics.
Frequently Asked Questions (FAQs)
What is the main difference between slow-twitch and fast-twitch fibres?
Slow-twitch fibres are fatigue-resistant and efficient for endurance, while fast-twitch fibres produce high force but fatigue quickly.
Can training change muscle fibre types?
Training improves fibre performance but does not completely change fibre type distribution.
How are muscle fibre types tested in IB SEHS exams?
Students are often asked to compare fibre types and apply them to sporting or movement scenarios.
