004 THE VARIOUS TYPES OF MUSCLE FIBRES

Every muscle consists of different types of muscle fibres which differ enormously in function. For the principles of training it is of importance to know and understand these differences because every type of muscle fibre requires specific training.
On the one hand there are the red or slow fibres, also called type I-fibres or Slow Twitch fibres (ST-fibres)
On the other hand there are the white or fast fibres, also called type II-fibres or Fast Twitch fibres (FT-fibres).

RED MUSCLE FIBRES = TYPE I-FIBRES = SLOW TWITCH FIBRES = ST-FIBRES = THE SLOW FIBRES
The well-blooded red muscle fibres deliver a predominantly aerobic energy supply. Because of that the red muscle fibres have a great aerobic capacity and a limited anaerobic capacity. The red muscle fibres determine stamina. They function slowly and are not easily tired. Because of this quality they can supply energy for endurance exercise for a long period of time.

WHITE MUSCLE FIBRES = TYPE II-FIBRES = FAST TWITCH FIBRES = FT-FIBRES = THE FAST FIBRES
The white muscle fibres are moderately supplied with blood and deliver energy predominantly anaerobic. So white muscle fibres have a big anaerobic and a small aerobic capacity. The white fibre system determines the sprint capacity of a cyclist. The white muscle fibres work fast and they are quickly exhausted. Fast, explosive efforts which call for the white fibres can be maintained only for a short period of time. The white fibres, the type II-fibres may be subdivided in type II-A and type II-B fibres.

  • The type II-A fibres are able to supply aerobic energy beside their anaerobic energy supply and thus support the type I fibres.
  • The type II-B fibres on the other hand are purely anaerobic and they scarcely have any function for an endurance effort.

THE RED AND WHITE MUSCLE FIBRES RATIO

The greater the number of FT-fibres the better sprinting capacity is and the greater the number of ST-fibres the better endurance capacity is. The ratio between ST- and FT-fibres may vary enormously in athletes.

The muscle fibre ratio is a fixed by birth for a great part. In other words: you are born as a sprinter or a pure endurance athlete. A sprinter has an ST/FT ratio of 50/50 and a marathoner may have an ST/FT ratio of 90/10

Long distance runners and road racer cyclists develop the slow muscle fibres by training, sprinters on the other hand develop the fast fibres. Sprinters and endurance athletes have a clearly different muscle structure.

The muscle fibre ratio, which is genetically laid down, determines if the athlete is a sprinter or en endurance type. But the system is not as rigid as described above. By specific training for endurance sprinters may improve their endurance capacity. This is brought about by the fact that this type of training increases the number of red fibres and decreases the number of white fibres. The specific endurance training stimulus converts white fibres into red ones. The opposite cannot be successful. A true endurance athlete will always be a poor sprinter, even if he will follow a sprint training regime. Sprinters may develop into better endurance athletes but their improved endurance capacity will be at the expense of their pure sprint.

With growing age sprinting capacity weakens faster than endurance capacity. The older the athlete the less explosive his sprint on account of a decrease in FT-fibres. Endurance capacity may be maintained up to high age.

The contraction power of the FT-fibres is much greater than that of the ST-fibres. The opposite goes for endurance.
CHARACTERISTICS OF RED AND WHITE MUSCLE FIBRES
White or fast muscle fibres
Type II-fibres or Fast Twitch (FT) fibres
Red or slow muscle fibres
Type I-fibres or Slow Twitch (ST) fibres
Explosiveness/sprinting power Endurance
Poor blood supply Good blood supply
Great anaerobic capacity Great aerobic capacity
Poor aerobic capacity Poor anaerobic capacity
Energy supply by lactate system and phosphate battery Energy supply by the oxygen system
Specific training does not convert red fibres into white fibres Specific training converts white fibres into red fibres
Endurance capacity short Endurance capacity long
Lactate formation high Lactate formation absent
Decrease of white fibres with growing age Slow decrease of red fibres with growing age
Easily exhausted Not easily exhausted
Speed high Speed low
Contraction power great Contraction power low