VIII. Types of Skeletal Muscle Fibers

A. Categories

1. Color varies according the content of myoglobin, and oxygen storing, reddish pigment

a. Red muscles- high myoglobin

b. White muscle- low myoglobin

2. Fiber diameter varies as do the cell’s allocations of mitochondria, blood capillaries, and sarcoplasmic reticulum

3. Contraction velocity and resistance to fatigue also differ between fibers

B. Classes of skeletal muscle fibers

1. Slow oxidative (type I) AKA slow twitch or fatigue resistance

a. Have high myoglobin and mitochondriab. Split ATP at slow rate but generate a lot by aerobic meansc. Tire slowly so used in postural muscles

2. Fast oxidative (Type II A) AKA fast twitch A or fatigue resistant

a. High mitochondria and myoglobin

b. Generate high ATP but split fast as well

c. Contract fast and tire slightly sooner than slow twitch

3. Fast glycolytic (type IIB) AKA fast twitch B or fatigable fibers

a. Low myoglobin and mitochondria

b. Make ATP by glycolysis and use it fast

c. Fatigue quickly4. Most muscles contain a mixture

but one unit will have only one type5. Can alter characteristics through exercise but will not change the

number of fibers

C. Anabolic steroids

1. Use can increase size strength and endurance of muscles

2. Have serious and life threatening results though