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 influence your strength and endurance.
There are three types of muscle fibre:
Slow twitch fibres (ST)
Fast twitch a fibres (FTa)
Fast twitch b fibres (FTb)
ST fibres contract relatively slowly. They have a high endurance capacity, do not tire easily and are used mainly in low-intensity, long-duration aerobic activities such as jogging.
FTa fibres in general are better suited to anaerobic activities than ST fibres and have relatively poor endurance. FTa fibres can produce more force than ST fibres but tire more easily. They have a lower endurance capacity and are used mainly during high-intensity activities such as a 1500-metre run.
FTb fibres are similar to FTa fibres but have a poor blood supply. They tire very quickly and are mainly used for explosive power activities such as sprinting and jumping. FTb fibres have the highest anaerobic capacity but the lowest endurance capacity.
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 one or two exceptions. In most people, for example, 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 fibres.
The proportion of different fibre types in your muscles dictates whether you are naturally suited to endurance, power or strength sports. If you have a high proportion of ST fibres (particularly in your leg muscles) you will be well-suited to endurance activities. If you have a higher proportion of FT fibres you are more likely to do well at sports involving power, sprints and strength.
Studies of elite athletes have revealed that distance runners have a significantly higher percentage of ST fibres(69-79%) in the gastrocnemius(calf muscle) compared with sprinters(24-27%),world-class marathon runners have been reported to posses up to 99% ST fibres in their gastrocnemius. Weightlifters have a higher percentage of FT fibres (56%) in the gastrocnemius compared with distance runners (21-31%)
Can you train the different muscle fibres?
Studies show that the distribution of the different fibre types is largely genetically determined. In fact, 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 percentage of FT and ST fibres, although as you age you tend to lose FT fibres.
It is possible to change the function of the muscle fibre types, however, through specific kinds of training. With aerobic training, FTa fibres can learn to use more oxygen and so assume some of the characteristics of ST fibres, i.e.they become more aerobic, while FTb fibres begin to assume some of the characteristics of FTa fibres and gain greater endurance. So, endurance training does not change the fibre type but will increase the muscles aerobic capacity. Strength training improves muscle strength and anaerobic capacity but will not change aerobic capacity.
There is evidence that heavy weight training can convert some FTb fibres into FTa fibres. Research also suggests that, with age, muscles become smaller because of loss of fibres, in particular FT fibres. However, loss of muscle size is not inevitable. Endurance and resistance training can help maintain the size of the ST and FT fibres respectively.
People with a high proportion of ST fibres will develop strength less readily than those with more FT fibres. 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 fibres can still be stronger than someone with a high proportion of FT fibres if they have plenty of motivation and follow the correct training and nutrition program. Your ability to reach your full potential is dependent on your mental attitude, training and diet.
There are three types of muscle fibre:
Slow twitch fibres (ST)
Fast twitch a fibres (FTa)
Fast twitch b fibres (FTb)
ST fibres contract relatively slowly. They have a high endurance capacity, do not tire easily and are used mainly in low-intensity, long-duration aerobic activities such as jogging.
FTa fibres in general are better suited to anaerobic activities than ST fibres and have relatively poor endurance. FTa fibres can produce more force than ST fibres but tire more easily. They have a lower endurance capacity and are used mainly during high-intensity activities such as a 1500-metre run.
FTb fibres are similar to FTa fibres but have a poor blood supply. They tire very quickly and are mainly used for explosive power activities such as sprinting and jumping. FTb fibres have the highest anaerobic capacity but the lowest endurance capacity.
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 one or two exceptions. In most people, for example, 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 fibres.
The proportion of different fibre types in your muscles dictates whether you are naturally suited to endurance, power or strength sports. If you have a high proportion of ST fibres (particularly in your leg muscles) you will be well-suited to endurance activities. If you have a higher proportion of FT fibres you are more likely to do well at sports involving power, sprints and strength.
Studies of elite athletes have revealed that distance runners have a significantly higher percentage of ST fibres(69-79%) in the gastrocnemius(calf muscle) compared with sprinters(24-27%),world-class marathon runners have been reported to posses up to 99% ST fibres in their gastrocnemius. Weightlifters have a higher percentage of FT fibres (56%) in the gastrocnemius compared with distance runners (21-31%)
Can you train the different muscle fibres?
Studies show that the distribution of the different fibre types is largely genetically determined. In fact, 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 percentage of FT and ST fibres, although as you age you tend to lose FT fibres.
It is possible to change the function of the muscle fibre types, however, through specific kinds of training. With aerobic training, FTa fibres can learn to use more oxygen and so assume some of the characteristics of ST fibres, i.e.they become more aerobic, while FTb fibres begin to assume some of the characteristics of FTa fibres and gain greater endurance. So, endurance training does not change the fibre type but will increase the muscles aerobic capacity. Strength training improves muscle strength and anaerobic capacity but will not change aerobic capacity.
There is evidence that heavy weight training can convert some FTb fibres into FTa fibres. Research also suggests that, with age, muscles become smaller because of loss of fibres, in particular FT fibres. However, loss of muscle size is not inevitable. Endurance and resistance training can help maintain the size of the ST and FT fibres respectively.
People with a high proportion of ST fibres will develop strength less readily than those with more FT fibres. 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 fibres can still be stronger than someone with a high proportion of FT fibres if they have plenty of motivation and follow the correct training and nutrition program. Your ability to reach your full potential is dependent on your mental attitude, training and diet.