Download VIII. Types of Skeletal Muscle Fibers

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
mitochondria
b. Split ATP at slow rate but
generate a lot by aerobic means
c. 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 quickly
4. Most muscles contain a mixture but
one unit will have only one type
5. 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