Muscle Fibre Types

Muscle Fibre Types

A little information about the different muscle fibre types can go far in assisting with working on your gains in both size and strength.

Some people seem to be able to produce great gains in muscle mass and strength. Others see only small, slow increases despite years of hard workouts, yet may be able to keep up long periods of aerobic activity with apparent ease. This is, in part, due to differences in the mix of muscle fibre types, which have an important effect on the type of activity your body is best suited ( e.g. aerobic or anaerobic ). Your particular distribution of fibre types influences your strength and endurance.

There are three types of muscle fiber:

  • Slow-twitch muscle fibers (ST)

  • Fast-twitch a muscle fibers (FTa)

  • Fast-twitch b muscle fibers (FTb)

ST fibers have a high endurance capacity, do not tire easily, and are used mainly in low-intensity, long-duration aerobic activities such as marathon runners.

FTa muscle fibres in general are better suited to anaerobic activities than ST fibres and have relatively poor endurance. FTa muscle fibres can produce more force than ST fibres but tire more easily and are used mainly during high-intensity activities such as a 1500-meter run.

FTb muscle fibres are similar to FTa muscle fibres but have a poor blood supply. They have the highest anaerobic capacity but the lowest endurance capacity. They tire very quickly and are mainly used for explosive power activities such as sprinting and jumping.

On average, most muscles are composed roughly of 50%ST, 25%FTa, and 25%FTb fibres, although the exact percentage varies between different muscles. Generally, a person’s leg and arm muscles have similar fibre compositions, however, there are few exceptions. In most people, the soleus muscle(lower calf)is almost entirely composed of ST fibres, whereas the deltoid muscles(shoulders) are comprised of a high proportion of FT muscle fibres.

Muscle Fibre Types: Slow Vs Fast Twitch

The proportion of different fibre types in your muscle dictates whether you are naturally suited to endurance, power, or strength sports. If you have a high proportion of ST muscle fibres you will be well-suited to endurance activities. If you have a higher proportion of FT muscle fibres you are more likely to do well at sports involving power, sprints, and strength.

The distribution of the different fiber types is largely genetically determined. Whether a muscle fibre becomes fast or slow-twitch is determined before birth and in the first few years of life. After this time, there is little you can do to change the percentage of FT and ST muscle fibres.

It is possible to change the function of muscle fibre types. With aerobic training, FTa muscle fibers can learn to use more oxygen and so assume some of the characteristics of ST fibers, i.e.they become more aerobic, while FTb fibers begin to develop some of the characteristics of FTa muscle fibers and gain greater endurance. Heavy weight training can convert some FTb muscle fibers into FTa muscle fibers. So, endurance training does not change the muscle fibre type but will increase the muscle aerobic capacity. Strength training improves muscle strength and anaerobic capacity but will not change aerobic capacity. Research also suggests that, with age, muscles become smaller because of the loss of fibers, in particular FT fibers. However, the loss of muscle size is not inevitable. Endurance and resistance training can help maintain the size of the ST and FT muscle fibres respectively.

People with a high proportion of ST muscle fibres will develop strength less readily than those with more FT fibers. However, it is not necessarily a straightforward relationship since there are other variables between strength and endurance, such as quality of training. Someone with a high proportion of ST fibers can still be stronger than someone with a high proportion of FT fibers if they have plenty of motivation and follow the correct training and nutrition programme. A person’s ability to reach full potential is dependent on their mental attitude, training, and diet.

Tomas is the leading personal trainer in Leeds.

Specialising in Circuit Training, Strength and Conditioning, Kick-Box Fitness and Rapid Fat Loss, Tomas has achieved phenomenal results for clients with a huge range of goals.

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