Fast Twitch vs Slow Twitch Muscle Fibres (Endurance or Strength)

Are you better as a Endurance Athlete or as a strength athelete, the body is already from birth better equiped to do one over the other, read on to find out why, knowing your strengths and weaknesses can be very helpful in choosing your path in Sports or Exercise Plans

Muscles have three different fibre types

• Type 1 (Slow Twitch or Slow Oxidative)

• Type 2a (Fast Twitch or Fast Oxiditave-Glycotic)

• Type 2b (Fast Twitch or Fast Glycotic)

Which Fibre type do i have?

Nobody has 100% of any type of muscle fibres, everybody consists of a combination of the three, people do generally have to some extent predominantly more of one than the others though, this is said to be primarily due to genetics and quite likely to be shared with that of your parents, though it is difficult to change which muscle fibre type you are dominant in, it is open to some degree of change through your daily activities and focus of your training or sport taken up, probably the best method we have of finding out the makeup of your muscle fibres is by a muscle biopsy, involving taking a sample of your muscle and analysing it under the microscope but this is far from practical to analyse the effect of your training on your distribution of muscle fibres, also although it may be a good indicator of your muscle fibre dominancy if a biopsy were to show that your femur muscle had predominantly more Type 1 fibres, it wouldn’t strictly mean that this was the case for all your muscles, as each muscle itself has its own ratio of the three fibre types, based on the different demands placed upon the muscle, it is suggested that muscles such as the rectus abdominus, erector spinae and all the deep core stabilising muscles, which are used frequently during any other movement as stabilisers and for general posture and maintaining upright, have a higher proportion of type 1 muscle fibres than the other muscles.

The Characteristics of the 3 fibre types

Type 1 fibres

- Contraction speed is slow

- Contraction strength is low

- Fatigue resistance is high

- Aerobic capacity is high

- Anaerobic capacity is low

- Myoglobin content is high

- Mitchondria in high amount

- Capillary density is high

- Motor unit size is small

Type 1 muscle fibres have a higher count of mitochondria which means it can process energy quicker, it receives a good blood supply since it has a high amount of capillaries, which means it has a good supply of oxygen, which helps to maintain the use of the aerobic energy system for longer, making type 1 fibres more effect for endurance events, the contraction strength and motor unit size is small in comparison to the other fibres, meaning it itself capable of quite the same exertion of force, its strong use of the aerobic system does however consequently mean its not quite as proficient at using the anaerobic energy system

Type 2a Fibres

- Contraction speed is fast

- Contraction strength is high

- Fatigue resistance is low

- Aerobic capacity is medium

- Anaerobic capacity is medium

- Myoglobin content is moderate

- Mitochondria in lesser amounts to type 1

- Capillary density is lesser than type 1

- Motor unit size is larger than type 1

Type 2a muscle fibres have a lesser count of mitochondria which means it cant process energy as quick as type 1, it receives lesser blood supply than type 1, since it has a lesser amount of capillaries, which means it has a poor supply of oxygen in comparison, however its aerobic and anaerobic capacity are both medium making it balanced at most activities, the contraction strength and motor unit size is larger in comparison to type 1 fibres, meaning its capable of exerting more strength.

Type 2b Fibres

- Contraction speed is the fastest

- Contraction strength is highest

- Fatigue resistance is lowest

- Aerobic capacity is low

- Anaerobic capacity is high

- Myoglobin content is low

- Mitochondria is low

- Capillary density is low

- Motor unit size is the largest

Type 2b muscle fibres are capable of exerting high force in their contractions, they recruit large number of motor neurons and fibres for actions and each fibre contracts at a fast rate to make the action promptly, however they contain low amounts of mitochondria so aren’t able to generate energy at the same rate at which they use it, which means they are forced to use the anaerobic energy system, consequently type 2b fibres have a high anaerobic capacity and a low aerobic capacity, capillary density is also the lowest which once again means oxygen supply isn’t as good, forcing most energy to be converted in the absence of oxygen aka anerobically.

Summary

Type 1 fibres are associated with a high level of endurance, opposed to type 2b fibres which are the polar opposite, being that they have low endurance, they are particularly suited to strength and power, type 2a fibres are the compromise of endurance and power

Their alternative names indicate how they operate

Type 1 (Slow Twitch or Slow Oxidative)

Slow twitch refers to the contraction speed of the fibre, whereas slow oxidative refers to its ability to create energy in the presence of oxygen (Oxidisation)

Type 2a (Fast Twitch or Fast Oxiditave-Glycotic)

Fast twitch refers to the fast contraction speed of the fibre, whereas oxidative-glycotic refers to the mix of energy production in the presence of oxygen and also energy produced anaerobically through the method of Glycolysis

Type 2b (Fast Twitch or Fast Glycotic)

Fast twitch refers to the fast contraction speed of the fibre, whereas glycotic refers to creating energy through breaking down glycogen in the process of glycolysis

Suitable sports based on Muscle fibre type

People with pre-dominantly type 1 fibres are best suited to events such as long distance running, power walking, long distance swimming and cycling.

People with pre-dominantly type 2a fibres are best suited for medium distance running, medium short distance swimming, hockey, basketball and football

People with pre-dominantly type 2b fibres are best suited to sprinting, boxing, rugby, American football, judo, shot-put, javelin, weight lifting, discus, relay racing, long jump and high jump

Somata Types

It is suggested that Ectomorphic bodied people have predominantly type 1 muscle fibres’, whereas mesamorphs have either Type 2a or 2b and endomorphs have type 2b muscle fibres, this once again suggest that your fibre type is pre-determined based on genetics, therefore also suggesting that you are born more suited to certain Olympic events than others, therefore perhaps it is important to pick a sport where your performance is aided by your genetic makeup and muscle fibre potential and also explain why some athletes have plateau and seemingly reached their genetic potential in their sport, since muscle fibre pre-domination is a hard thing to change

“So endurance training does not change the fibre type but will increase the muscles aerobic capacity, it is not however possible for changes to occur in the opposite direction – i.e. for Slow twitch fibres to assume the characteristics of FT Fibres” – (The complete guide to strength training, Anita Bean 2007.)

Therefore a weight lifter with predominantly Type 1 Slow twitch fibres would not be able to change their fibre type and since Type 1 fibres don’t have much contractile strength, are not suited for such an event.