Muscle Stimulation &
Exercise
4-5 November 2014
Response to Stimulation
 Muscles have graded responses – they contract to different
degrees, depending upon the frequency and strength of
stimulation
Response to Stimulation
 If a nerve fires once
(unusual), the
muscle contracts and
relaxes in a twitch
 If the nerve fires
rapidly in succession,
then the muscle does
not relax fully in
between impulses –
resulting in tetany
(a smooth, prolonged
contraction)
Response to Stimulation
Note:
tetanus ≠ tetanus
Tetanus (the type of
muscle contraction)
is different than
tetanus the disease
caused by a bacteria
(commonly called
lockjaw)
Response to Stimulation
The strength of
contraction also depends
on how many muscle
fibers are stimulated.
The more muscle fibers
stimulated, the greater
the contraction of the
muscle.
Quick Review
What vocab word describes the fact that
muscles may contract to different degrees?
Graded response
What two factors determine the extent to
which a muscle contracts?
Frequency of stimulation and
number of cells stimulated
Muscle Metabolism
Muscle contraction requires
enormous amounts of
energy in the form of ATP.
The amount of ATP stored
in the cell only lasts for ~5
seconds!
The rest of the ATP must be
regenerated, using one of
three pathways.
Muscle Metabolism
Pathway 1: Direct phosphorylation by creatine phosphate
 Fast!
 No O2 required
 Quickly used up
 Only in muscle
cells
Muscle Metabolism
Pathway 2: Anaerobic glycolysis and lactic acid formation




Medium speed
No O2 required
Less efficient
Produces
lactic acid
 Only in muscle
cells
Muscle Metabolism
Pathway 2: Anaerobic glycolysis and lactic acid formation
Misconception alert!
Lactic acid build-up
is not responsible for
muscle soreness the
day after exercise
(that’s due to cell
damage).
Muscle Metabolism
Pathway 2: Anaerobic glycolysis and lactic acid formation
Lactic acid build-up
is responsible for the
burning feeling
during exercise.
Also, lactic acid
build-up increases
muscle fatigue
(inability of muscle to
contract when
stimulated)
Muscle Metabolism
Pathway 3: Aerobic respiration




Slow
Long-lasting
All cells
Requires O2
Muscle Metabolism
Which energy pathway is better?
CP and anaerobic supply
energy at a fast rate (for
maximum performance)
but for a short term only.
Examples:
 Sprinting
 Any sport with bursts of
energy & quick changes
(e.g. Volleyball, b-ball)
 Start of exercise
Muscle Metabolism
Which energy pathway is better?
Aerobic can provide
energy for hours without
fatigue
But, muscles are not
working at peak levels
Examples: cycling, marathon
Muscle Metabolism
Sports & Energy Systems
Muscle Metabolism
Oxygen Debt
All non-aerobic energy use causes changes in the muscle
that need to be reversed after the exercise is over
 O2, ATP, creatine phosphate, and glycogen reserves
need to be replenished
 Lactic acid needs be broken down
Oxygen debt is the extra amount of oxygen that must be
taken in for these restorative processes.
This is why you breathe deeply for a while after intense
exercise.
Think, Pair, Share
Scholar with shorter hair:
Name the reactants and products of each energy
system.
Which two energy systems are only used in muscles?
Scholar with longer hair:
Which two energy systems lead to oxygen debt?
Which energy system(s) predominate in the following
activities: running for your life, hiking, lifting heavy
furniture
Critical Thinking 1
The graph below indicates the amount of lactic acid
produced by muscle cells as a function of power (energy /
time).
1) Describe how lactic acid production varies with power.
2) Explain
the shape of the
graph using
your knowledge
of energy
systems
Critical Thinking 1
1) Lactic acid increases very slowly from 150 W to 250
W but begins to increase dramatically at about 275
W.
2) At around 275 W, the rate of energy required by the
muscle cells is too high, so the body switches from
aerobic metabolism
to anaerobic
metabolism. This
point is known as
aerobic threshold.
Exercise & Muscles
Isotonic vs Isometric Contractions
Isotonic contractions occur whenever the muscles
shorten, causing movement
(e.g. weight lifting, running, swimming, jumping, etc.)
Isometric contractions occur whenever the muscle’s
tension increases without actually shortening. This
happens when you try to move an immovable object.
(e.g. pushing against a wall; many yoga exercises, etc.)
Exercise & Muscles
Aerobic vs Resistance Exercise
Aerobic exercise (aka endurance or cardiovascular) –
builds the aerobic endurance of muscles
 Examples: jogging, biking
 Increases blood supply to muscles; # of mitochondria, &
amount of stored oxygen
 Benefits






Greater resistance to fatigue
Better heart and lung function
Improved digestion
Improved bone density
Reduced risk of metabolic disorder
Increased immune system function
Exercise & Muscles
Aerobic vs Resistance Exercise
Resistance exercise (aka weight training) – focuses on
isometric contractions & forcing muscle to contract with
as much force as possible
 Examples: weights, some yoga exercises, pushups, situps,
 Increases the number of actin and myosin fibers, resulting in
larger muscles
 Benefits
 Greater strength
 Greater muscle mass = greater metabolism
 Increased bone density
Exercise & Muscles
Exercise
recommendations
for healthy adults
age 18-65 from CDC
Exercise & Muscles
Muscle tone and muscle wasting
 Muscles quickly deteriorate when not used
 Lose 5-10% muscle mass per week with bed rest
 Lose 20% muscle strength in one week of bed rest
 Muscle strength plateaus at ~30% original strength after ~6
weeks of bed rest
 Our body maintains muscle tone by systematically
stimulating and partially contracting muscles around
the body
 Electrical muscle stimulators can also help prevent
muscle atrophy following a stroke, injury, or surgery
Think, Pair, Share
1. Compare and contrast isotonic and isometric
exercises, and provide an example of each
2. Compare and contrast resistance and aerobic
exercise, and provide an example of each
3. Why is exercise necessary for our muscles?
4. How does exercise help our body function?
Closure
What were our objectives today?
What did you learn about these objectives?
How does what we learned today tie to our unit
question?
Critical Thinking 2 – Exit Ticket
The graph below indicates the amount of lactic acid
produced by muscle cells as a function running pace.
1) Describe the data.
1) Explain
the data using
your
knowledge
of energy
systems and
exercise