Muscle Fibre Types and Fatigue in Exercise

Study Notes

Muscle Fibre Types

Slow-twitch Fibres

Also known as Type I fibres
Characteristics:
- High endurance and resistance to fatigue
- Low force production
- High myoglobin content, allowing for high oxygen storage
- High mitochondrial density, allowing for efficient aerobic energy production
Functions:
- Designed for low-intensity, long-duration activities (e.g., distance running)
- Play a crucial role in posture, balance, and stabilisation

Muscle Fibre Distribution

Human skeletal muscles consist of a mixture of fibre types
Typical distribution:
- Type I (slow-twitch): 40-60%
- Type IIA (fast-twitch): 20-40%
- Type IIB (fast-twitch): 10-30%
Distribution can vary depending on factors such as:
- Muscle group (e.g., leg muscles tend to have more Type I fibres)
- Training status (e.g., endurance-trained athletes tend to have more Type I fibres)
- Genetics

Fast-twitch Fibres

Also known as Type II fibres (subdivided into Type IIA and Type IIB)
Characteristics:
- High force production
- Low endurance and high fatigue rate
- Low myoglobin content, limiting oxygen storage
- Low mitochondrial density, relying on anaerobic energy production
Functions:
- Designed for high-intensity, short-duration activities (e.g., sprinting)
- Important for rapid, powerful movements

Muscle Fatigue

Defined as a decline in muscle force production over time
Types of fatigue:
- Peripheral fatigue: due to changes in the muscle itself (e.g., ion imbalance, metabolic byproducts)
- Central fatigue: due to changes in the nervous system (e.g., reduced motor neuron activation)
Factors contributing to muscle fatigue:
- Muscle fibre type (fast-twitch fibres are more prone to fatigue)
- Intensity and duration of exercise
- Environmental factors (e.g., temperature, humidity)
- Nutritional and hydration status

Description

Understand the characteristics, functions and distribution of slow-twitch and fast-twitch muscle fibres, and learn about muscle fatigue and its contributing factors. This quiz covers the basics of muscle physiology and exercise science.