Facts about muscles

Muscle physiology

Skeletal muscle is made up of bundles of individual muscle fibers called myocytes. Each myocyte contains many myofibrils, which are strands of protein filaments (actin and myosin) that grab on to each other and pull towards one another. This shortens the muscle and causes muscle contraction. 


Muslce fibers are catagoried as type I and type ii fibers.

  • Type I = Slow twitch fibers
  • Type ii = Fast twitch fibers
  • Type ii can be further categorised into Type iia and Type iib

Human muscles contain a mix of both fast and slow twitch fibers.


Slow Twitch (Type I)
These are the fibers that will kick into action to help you run a marathon or longer endurance event. They work aerobically. Oxygen is required by the muscle to produce ATP, which fuels the muscle. 


Fast Twitch (Type II)

These are fibers which help your muscle work at a short intense rate. This could be a short burst of strength when power lifting or a rapid explosive sprint in a short race. These muscles work short and fast and fatigue far quicker than slow twitch muscles.


Type IIa Fibers

These are intermediate fast twitch fibers and are a combination of bother type I and type II muslce fibers. They can be used aerobically and anaerobically to produce energy.


Type IIb Fibers
These are fast twitch fibers that use anaerobic metabolism for energy. They are responsible for the explosive powerful bursts of rapid speed. It is the fastest of the muscle types are firing a contraction but also have the fastest rate of fatigue burn out.

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