Module 9.14 Fast, slow, and intermediate skeletal muscle fibers differ in size, internal structure, metabolism, and resistance to fatigue.
slow fibers also contain a red pigment myoglobin,
a globular protein that is structurally related to hemoglobin, the red auction carrying pigment in blood
because slow fibers have both an excessive capillary supply and a high concentration of myoglobin, skeletal muscles dominated by slow fibers appear
darker in color
fast fibers have large diameters and contained
densely packed myofibrils, large glycogen reserves, and relatively few mitochondria
Intermediate fibers have more extensive capillary networks around them and have more resistance to fatigue than
fast fibers
most of the skeletal muscle fibers in the body are called
fast fibers because they can reach a peak twitch tension in 0.01 seconds or less after stimulation
Intermediate fibers are more closely related to
fast fibers because they contain more myoglobin and look relatively pale
the human body has three major types of skeletal muscles
fast fibers, slow fibers, an intermediate fibers
The percentage of fast versus slow fibers in each muscle is determined
genetically
There are no slow muscle fibers in the muscles of the
hands or eyes
the ratio of intermediate fibers too fast fibers can
increase as a result of athletic training. For example, if a muscle is used repeatedly for endurance events, some of the fast fibers will develop the appearance in functional capabilities as intermediate fibers
both myoglobin and hemoglobin respectively bind to
oxygen molecules
slow muscle fibers are surrounded by a more extensive network of capillaries then fast muscle tissue, so they have a dramatically higher
oxygen supply to support mitochondrial activity
slow fibers are specialized to continue contracting for extended
periods of time , long after a fast fiber word become fatigue
the tension produced by a muscle fiber is directly proportional to the number of myofibrils, so muscles dominated by fast fibers produced
powerful contractions
skeletal muscles demonstrated by fast fibers appear pale and are often called
white muscle
Fast muscle fibers and slow muscle fibers have different
sizes, densities, number of mitochondria, and amount of capillary supply.
Many back and calf muscles are dominated by
slow fibers because these muscles are continuously contracting in order to maintain upright posture
myoglobin is most abundant and slow fibers
so resting slow fibers contain substantial oxygen reserves that can be mobilized during a contraction
however, fast fibers fatigue rapidly because
their contractions use ATP in massive amounts, and they have relatively few mitochondria to generate ATP . as a result, prolonged activity is supported primarily by anaerobic metabolism
slow fibers have only about half the diameter of fast fibers and take
three times as long to reach peak tension after stimulation