What's the difference
between type 1 muscle fibers and the equally descript
type 2 muscle fibers? And I hate it when
they give things names like type 1 and type 2. That's not really descriptive. That doesn't tell me
a lot of information about these types
of muscle fibers. So what I do is I
get back at them. I come up with one golden rule. And this one golden rule will
help me go through a table, like we're about to do
right here, to differentiate between type 1 and
type 2 muscle fibers. So the golden rule I'm going
to have for this table here is that mitochondria--
whoops, look how I wrote that "i" there. Mitochondria are present in
greater quantities in your type 1 muscle fibers, type 1. So mitochondria are more
prevalent in type 1 muscle fibers than in type 2. And just based on
that knowledge alone, we should be able to go through
and fill out this table. All right, so let's
start from the top. I may have alluded to it here
through the way I wrote this out, but the color type 1 muscle
fibers are often noted as? Red. And why do you think that is? Well, what are
mitochondria used for? Mitochondria are used
in biochemical processes that help us make energy. And the main process
they function in that I'm going to
reference a couple of times is called oxidative
phosphorylation. Now, what is that
term mean to you? What does that suggest? What are the two things
that are probably involved in oxidative
phosphorylation? So just as the name suggests,
oxidative means oxygen is going to be involved here. And then phosphorylation
means that something is going to receive
a phosphate group. Phosphoryl- -ation, something
will receive a phosphate group. So the oxidative
part applies here to red, the same way that
the color red shows up in our arteries. Think about it. Why are arteries red,
and why are veins blue? Well, arteries have more
oxygen than veins do. And because of that, the color
of our type 1 muscle fibers will be red because they
produce more energy from oxygen than type 2 muscle fibers do. More oxygen is present in
type 1, so they're red. And so we could say then
that our type 2 muscle fibers will be white. All right, what about
the speed of contraction that we see here? How fast do type 1
muscle fibers contract? Well, let's think about the
process of making energy with mitochondria. If type 1 muscle fibers rely
on mitochondria for energy, think about all
the processes that have to go into
making energy through oxidative phosphorylation. You can't just do
this right away. You have to have
glycolysis happen. You have to have the
Krebs cycle occur. You need to make NADH and
FADH2, all of these cofactors that have to go into this
electron transport chain. There's a lot of things
that have to be done. So mitochondria take a
while to make energy. So that means that the
contraction speed here is also going to be slow
because it takes a while to make that energy. And so on the flip
side, that means that the contraction speed of
type 2, or white muscle fibers, is going to be fast. What about the
conduction velocity? How quickly are we going
to be able to receive a neuronal impulse or a nerve
signal to type 1 muscle fibers to contract? This is also going to be slow. And the term here is
called "slow twitch." And I remember that the same way
I remember that the contraction speed is slow in
type 1 muscle fibers. On the flip side, we call
type 2 muscle fibers fast twitch muscle fibers. All right, now, what
types of activities do you think type
1 muscle fibers are going to be involved in? Well, oxidative phosphorylation
has another name. The mitochondria is used for a
specific type of respiration. That's a cue term right there. That's something that should
cue another word in your mind. If mitochondria is involved for
a type of cellular respiration, that type of
[INAUDIBLE]-- aerobic. Aerobic respiration requires
mitochondria to be present. And so because there's more
mitochondria in type 1 muscle fibers, type 1
muscle fibers will undergo aerobic respiration. What about type 2? Well, because they don't
have as much mitochondria, they're going to have to
undergo anaerobic respiration, or respiration in the
absence of oxygen. That's what a aerobic
means-- "by using oxygen." Anaerobic means
"without oxygen." OK, how long will these
muscle fibers be contracting? Well, let's think about
how much energy we're making if we have
mitochondria versus if we don't have mitochondria. We make a lot more energy
if we have mitochondria. And so the duration of
contraction then will be long. You're going to have longer
contractions when you're able to make a lot
more energy or ATP, because you've got mitochondria
present in greater quantities. If you lack mitochondria or you
undergo anaerobic respiration because you can't undergo
oxidative phosphorylation as much, you're going to have a lot
of short-duration contractions. What's the difference
between these two? Well, if I'm having a
long-duration contraction, that's something like
the muscles in my back that I use for standing
or in my legs so that way I can walk at a certain pace. Short-duration muscle fibers,
those that contract really quickly and that's
it, are things like the ones in our arms
when we shake somebody's hand or if we flick something
with our finger. If we do that for a
long period of time, we're going to get really tired. So these muscle
fibers are not meant to be working for
the entire day. If we're in line
at Disneyland, we want to be using our
long-duration muscle fibers, the ones in our back,
in our glutes, in our legs. So that way, we can stand
for a long period of time. We don't want to be standing
on our hands or our fingers because we won't be able to last
by using type 2 muscle fibers. All right. So which of these
types of muscle fibers are most likely to fatigue? Well, if type 1
muscle fibers are able to contract for
a long period of time, we say then that they
are fatigue resistant. They are fatigue resistant
because we have enough energy for type 1 muscle
fibers to contract for a long period of time. But type 2 muscle fibers
do not have as much energy, because they don't have
as much mitochondria. And so as such,
they easily fatigue. So I'll write easily right here. They are not resistant. What about the
power of contraction that's associated with
type 1 muscle fibers? Well, I talked about some
pretty heavy muscles just now, the ones in your
glutes, your back. And if we're having long
durations of contraction, these are going to be some
pretty big, powerful muscle groups. And so I'll write strong here. Because again, noting back
to the mitochondria analogy, if we have a lot more
mitochondria present in type 1 muscle fibers, they're going
to have a lot more energy to contract and more
muscles contracting. More muscle cells
contracting at the same time elicits a stronger, more
powerful contraction overall. On the flip side,
type 2 muscle fibers-- not enough mitochondria,
not enough energy, not enough power-- so these are
going to be weak contractions. And lastly, how do we store our
energy in type 1 versus type 2? This might be a
little bit of a trick, but you can figure this out. With mitochondria, we
make a lot of energy. And if we have a
lot of energy, are we going to leave that
sitting around as ATP? No, ATP is a really labile,
or a really reactive molecule. If we have it there,
we're anticipating it to be used right away. And so what type
1 muscle fibers do is they store their
energy in triglycerides, these fatty substances. And so that's why we
put energy into fat. So that way, we can use it
later on for the stronger, longer-duration contractions. If we want it to contract right
away we'll just use raw ATP. And so the ATP that's
just sitting around is used in type 2 muscle fibers. Also, we'll use something
called creatine phosphate, which is very similar to
ATP in the sense that it has a phosphate
group that it'll be able to donate
to produce energy. And so this phosphate group
is very reactive, very labile. If it's sitting
around, that means it's going to be
used any second now for a quick,
short-duration contraction. So by using this
one golden rule here that mitochondria are more
prevalent in type 1 muscle fibers, we can figure out
this whole table here. And that's the
difference between type 1 and type 2 muscle fibers.