Let’s now discuss muscle fiber types because
not all muscle behaves in the same way.
We have three main
muscle fiber types.
We have two that are considered white muscle
and one that’s considered red muscle.
What makes the red muscle
red is the myoglobin
that is involved in that
particular muscle fiber type.
Now when we break these into
these artificial kind of slow
oxidative, fast glycolytic,
fast oxidative glycolytic,
we are really more on a continuum
than we are in individual bins.
But it’s helpful in our minds to
be able to bin them so we can best
approach a potential problem
with the muscular system.
So let’s now discuss a
couple of different
features of each of these
skeletal muscle types.
So myosin ATP activity in slow
oxidative fibers is slower
than it is in fast glycolytic
or fast oxidative glycolytic.
component that’s different
between the fiber types
is fatigue resistance.
Slow oxidative fibers don’t fatigue as
quickly as fast glycolytic fibers do.
And then, fast oxidative glycolytic
fibers fatigue less than fast glycolytic.
So it sets up this system where you
have slow oxidative glycolytic,
to fast oxidative glycolytic,
to then fast glycolytic in terms
of their fatigue resistance.
In terms of oxidative capacity, this is the
ability to utilize oxygen to make ATP.
This is going through the glycolysis followed
by the pyruvate dehydrogenase complex,
followed by the TCA cycle or the Krebs
cycle, and then oxidative phosphorylation.
Slow oxidative fibers have a
high capacity to utilize oxygen,
followed by fast oxidative glycolytic,
and then finally, fast glycolytic.
The opposite is true for
Fast glycolytic fibers do not need oxygen
to perform high amounts of activity.
In fact, they rather go through
glycolysis and then over through the
lactate dehydrogenase reaction to
form lactate, to get energy quicker.
In terms of myoglobin content, it’s
very high in slow oxidative fibers.
In fact, that’s probably what
makes it red in appearance.
In terms of mitochondrial
size and number,
these mitochondrial components are the
kind of power house of an individual cell.
It’s where the oxygen is
going to be utilized as a
final electronic scepter in
As you can imagine in slow
oxidative fibers, that volume
is high in those fibers and
lowest in the fast glycolytic
with the fast oxidative glycolytic
being more moderate in nature.
In terms of capillaries that
are surrounding the muscle,
the density is very high
with slow oxidative fibers,
low with fast glycolytic, and with fast
oxidative glycolytic they’re in the middle.
By knowing these inherent properties of muscle fiber types,
you’ll be able to better think about
how a particular muscle will respond.
Some muscles have a predominance
of slow oxidative fibers,
others have a predominance
of fast glycolytic fibers.
But by knowing that, you’ll know
what their oxidative capacity is,
their glycolytic capacity, their
ability to resist fatigue,
all based upon the
muscle fiber types.
How do you determine
someone’s muscle fiber type?
You take a muscle biopsy
and then you would
stain for some of these
There are some individuals that have
very high fast glycolytic fibers
in certain muscle groups and that’s one
of the reasons that makes them fast.
In other individuals, they
have higher slow oxidative
fibers and that’s what makes
them a good endurance athlete.
Having this repertoire of knowing
where these muscle fiber types are
and which do what helps you to
understand the physiological function.