Background:
Did you know you have more than 600 muscles in your body? They do everything from pumping
blood throughout your body to helping you lift your heavy backpack. You control some of your
muscles, while others — like your heart — do their jobs without you thinking about them at all.
Muscle cells need to produce energy so they can work. Muscle cells rely on aerobic
[​ai-​ROH​-bik​] respiration for their energy needs. ​Aerobic​ means “with oxygen” so ​aerobic
respiration​ is the process of respiration using oxygen. You’ve learned about this before; we
called it ​cellular respiration​! Because it uses oxygen, cellular respiration is also called aerobic
respiration. Remember that cellular respiration is the process of using oxygen to breakdown
glucose (food) into energy that cells need to function. The waste products of cellular respiration
are carbon dioxide and water.
But what happens when there’s no oxygen handy? Like when you’re exercising really hard, and
your lungs can’t supply your muscle cells with all the oxygen they need? In that case, the cells
go with a backup plan called fermentation, where glucose is combined with carbon dioxide,
instead of oxygen. It doesn’t make as much energy as aerobic respiration. But it works for a
short time.
This kind of respiration, in which something other than oxygen is used to release the energy
from glucose, is called anaerobic respiration (anaerobic means “without oxygen”). In anaerobic
respiration (fermentation) the waste product is lactic acid. Too much anaerobic respiration and
your body builds up lactic acid causing your muscles to experience fatigue. Lactic acid also
causes a burning sensation in your muscles. This reduces your muscle’s ability to function and
your body desires rest to build up its oxygen supplies once again. Following a period of the rest
the muscle cells regain their normal condition and can function normally once again.
Source1​, ​source2​, ​source3
Questions:
1. What causes muscles to fatigue? ​Hint: this is
also what causes the burning sensation in your
muscles​.
2. Why do your muscle cells switch from aerobic
(​with oxygen​) to anaerobic (​without oxygen​)
respiration?
image source
One of the objectives of this unit is:
The student will be able to describe the structure, function, and interdependence of human body
systems.
3. Predict: What other body system(s) work together with the muscular system? Explain
why. ​Hint: think about the cellular respiration equation
Background Info:
Your muscles need oxygen and glucose in order to function. When there is no
oxygen available the cells go with a backup plan called fermentation, where
glucose is combined with carbon dioxide, instead of oxygen. A waste product
called lactic acid is produced. A buildup of lactic acid decreases the muscle's’
ability to contract and muscle fatigue sets in.
Do this:
1. Hold a textbook in each hand.
2. Raise one arm straight out
parallel to the ground and the
other arm down at your side.
Answer these:
1. How long did you hold the book before fatigue got the better of you?
________ minutes ________ seconds
2. Which arm felt the fatigue the most?
3. Which muscles experienced the most fatigue? ​Click here for a hint​.
a. biceps
b. triceps
c. deltoids
d. pectoralis major
Source
Background Info:
Your muscles need oxygen
and glucose in order to
function. When there is no
oxygen available the cells go
with a backup plan called
fermentation, where glucose
is combined with carbon
dioxide, instead of oxygen. A
waste product called lactic
acid is produced. A buildup of
lactic acid decreases the
muscle's’ ability to contract
and muscle fatigue sets in.
Do this:
1. Sit against the wall with your knees bent at a 90​o​ angle. Hold this position for
as long as it takes to feel muscle fatigue.
2. If it’s been more than 4 minutes you ain’t doin’ it right!
Answer these:
1. How long did you sit before your legs started to burn like crazy?
__________ minutes __________ seconds
2. How did it feel to try to walk right after sitting against the wall?
3. The funny feeling in your legs is called muscle fatigue. Fatigue is caused by
a buildup of __________ __________ in the muscle.
Source
Background Info:
Your heart is made up of a very special type of muscle called Cardiac Muscle. It
keeps working hard from before the day you are born until the moment of your
death. It never gets to stop and rest like your skeletal muscles do. Cardiac muscle
does not experience muscle fatigue but skeletal muscles do. Here we will compare
cardiac and skeletal muscles with the help of your strong arm and a “tennis ball
heart”.
Do this:
1. Extend your arm out in
front of you and using
your hand, squeeze
the tennis ball hard
one time each second.
This is how hard your
heart works…and it
doesn’t complain!
Answer these:
1. How is your heart (cardiac) muscle different from your arm (skeletal)
muscle? ​just compare how tired your arm got doing the work of the heart
2. One reason cardiac muscle doesn’t experience fatigue is that it has more
mitochondria. What would be another reason? ​Hint: what do cells need?
3. Does skeletal muscle experience fatigue? So about how long did you “live”?
_____ minutes
Source
Background Info:
After just 7 seconds of use the muscle begins producing lactic acid as glucose &
carbon dioxide is broken down to provide energy. To help delay muscle fatigue,
the muscle fibers are constantly switching on and off to allow individual fibers a
moment to rest. This activity will demonstrate the effects of action of muscle fibers.
Do this:
1. Hold a popsicle stick in front of you,
parallel to the table top.
2. Place a bent paper clip on the stick.
3. Raise the stick until the legs of the
paper clip just touch the table. The top of
the paper clip should rest on the stick.
4. Hold the stick as steady as you can
for about 30 seconds and observe.
5. Grip the stick tighter and repeat
step 4.
Answer these:
1. What happened to the paper clip
even when you kept your hand steady?
2. What caused this?​ Hint: Read the introduction
Source
Background Info:
Your muscles need oxygen and glucose in order to function. When there is no
oxygen available the cells go with a backup plan called fermentation, where
glucose is combined with carbon dioxide, instead of oxygen. A waste product
called lactic acid is produced. A buildup of lactic acid decreases the muscle's’
ability to contract and muscle fatigue sets in.
Do this:
1. Hold a clothespin between
your thumb and index finger and
count how many times you can
squeeze it in one minute. Record
2. Now, without resting, squeeze
it as fast as you can for a second
minute. Record how many times you
can squeeze it.
Answer these:
1. How many times did you squeeze the clothespin the first minute? _______
2. How many times did you squeeze the clothespin the 2​nd​ minute? ______
3. The soreness in your and arm is called muscle fatigue. Fatigue is caused by
a buildup of ________ _________ in your muscles. ​Hint: read the intro
4. Why did you feel fatigue in your forearm rather than your fingers?
Source