Effect on Slow and Fast Twitch Muscle Fibres
There are two types of muscle fibre:
Fast-twitch fibres contract quickly and release energy rapidly however, they fatigue rapidly due to anaerobic metabolism providing the energy. They use the alactic system (ATP-PC) and the lactic acid system for energy to perform explosive movements that aren't going to be continuous. The body preferentially uses fast-twitch fibres to perform explosive type activities such as weight-lifting, field athletics and sprint track athletics e.g. 100m and 200m sprint.
The effect of training on fast and slow twitch muscle fibres directly affects muscle hypertrophy. When the different muscle fibres are trained they will change according to their type and the type of training. Fast twitch muscle fibres, trained with explosive movements, will increase in size and slow twitch muscle fibres will benefit from endurance training and also undergo hypertrophy.
Training causes structural changes in muscle fibres, leading to hypertrophy. The growth and cross sectional size increase of the muscle is due to increases in:
The individual's ratio of fast-twitch to slow-twitch muscle fibre is genetically determined, making them more suited to certain sports or activities. The ratio of both types of muscle fibre varies in each individual and each muscle. In summary:
Refer to the digram at the bottom of the page for a diagrammatic representation:
Sport specific training encourages the development and adaptation of each type of muscle fibre. Fast-twitch muscle fibres benefit most by anaerobic training, such as sprint or interval training and resistance training. Slow-twitch muscle fibres benefit most from endurance type activities that engage the aerobic system, such as running, cycling and swimming.
The adaptations that can occur in slow twitch muscles in response to aerobic training are:
The adaptations that can occur in fast twitch muscles in response to aerobic training are:
- slow-twitch muscle fibres
- fast-twitch muscle fibres.
Fast-twitch fibres contract quickly and release energy rapidly however, they fatigue rapidly due to anaerobic metabolism providing the energy. They use the alactic system (ATP-PC) and the lactic acid system for energy to perform explosive movements that aren't going to be continuous. The body preferentially uses fast-twitch fibres to perform explosive type activities such as weight-lifting, field athletics and sprint track athletics e.g. 100m and 200m sprint.
The effect of training on fast and slow twitch muscle fibres directly affects muscle hypertrophy. When the different muscle fibres are trained they will change according to their type and the type of training. Fast twitch muscle fibres, trained with explosive movements, will increase in size and slow twitch muscle fibres will benefit from endurance training and also undergo hypertrophy.
Training causes structural changes in muscle fibres, leading to hypertrophy. The growth and cross sectional size increase of the muscle is due to increases in:
- Actin and myosin filament- protein filaments that help produce muscle actions
- Myofibrils- contractile elements of skeletal muscle
- Connective tissue- tissue that surrounds and supports muscle
The individual's ratio of fast-twitch to slow-twitch muscle fibre is genetically determined, making them more suited to certain sports or activities. The ratio of both types of muscle fibre varies in each individual and each muscle. In summary:
- Ratio of fast to slow-twitch fibres is thought to be genetically determined.
- The metabolic capabilities of both types of fibres can improve through specific strength and endurance training.
- Sprinters and weight lifters have a large percentage of fast-twitch fibres.
- Marathon runners generally have a higher percentage of slow twitch fibres.
- Muscles that primarily maintain posture against gravity (core strength) require more endurance and generally have a higher percentage of slow-twitch fibres.
- Muscles that produce powerful, rapid, explosive strength movements tend to have a greater percentage of fast-twitch fibres e.g. muscles in the legs.
Refer to the digram at the bottom of the page for a diagrammatic representation:
Sport specific training encourages the development and adaptation of each type of muscle fibre. Fast-twitch muscle fibres benefit most by anaerobic training, such as sprint or interval training and resistance training. Slow-twitch muscle fibres benefit most from endurance type activities that engage the aerobic system, such as running, cycling and swimming.
The adaptations that can occur in slow twitch muscles in response to aerobic training are:
- hypertrophy of slow-twitch muscle fibres
- increased capillary supply to muscle fibres, improving gaseous exchange & movement of nutrients and waste products
- increased number and size of mitochondria (energy factory of cells) enabling more efficient energy production
- significant increase in myoglobin content (transports oxygen from the cell membrane to mitochondria)
The adaptations that can occur in fast twitch muscles in response to aerobic training are:
- increase and efficiency of ATP/PC supply
- increased glycolytic enzymes which improve functioning of the cell
- hypertrophy of red-twitch muscle fibres
- increased tolerance of lactic acid, allowing performance to be sustained for longer periods
- muscle contractions can be made more forcefully and quickly as there are a greater volume of fast-twitch fibre
A diagrammatic representation of the fast twitch muscle fibres and sow twitch muscle fibres. Genetics determines the ratio and if this person was more suited to powerful sports they would have more light coloured or fast twitch muscle fibres. If the individual was more suited to endurance aerobic activities then there would be a majority of dark or slow twitch muscle fibres.