1. Muscle Stimulation & Exercise
4-5 November 2014

2. Response to Stimulation
Muscles have graded responses – they contract to different degrees, depending upon the frequency and strength of stimulation

3. 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)

4. 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)

5. 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.

6. Quick Review
What vocab word describes the fact that muscles may contract to different degrees? What two factors determine the extent to which a muscle contracts?
Graded response
Frequency of stimulation and number of cells stimulated

7. 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.

8. Muscle Metabolism
Pathway 1: Direct phosphorylation by creatine phosphate
Fast!
No O2 required
Quickly used up
Only in muscle
cells

9. Muscle Metabolism
Pathway 2: Anaerobic glycolysis and lactic acid formation
Medium speed
No O2 required
Less efficient
Produces
lactic acid
Only in muscle
cells

10. 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).

11. 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)

12. Muscle Metabolism Pathway 3: Aerobic respiration Slow Long-lasting
All cells
Requires O2

13. 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

14. 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

15. Muscle Metabolism
Sports & Energy Systems

16. 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.
These processes all require oxygen

17. 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
These processes all require oxygen

18. Critical Thinking 1
The graph below indicates the amount of lactic acid produced by muscle cells as a function of power (energy / time).
Describe how lactic acid production varies with power.
Explain
the shape of the
graph using
your knowledge
of energy
systems
These processes all require oxygen

19. Critical Thinking 1
Lactic acid increases very slowly from 150 W to 250 W but begins to increase dramatically at about 275 W.
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.
These processes all require oxygen

20. 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.)
These processes all require oxygen

21. 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
These processes all require oxygen

22. 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
These processes all require oxygen

23. Exercise & Muscles
Exercise recommendations for healthy adults age from CDC
These processes all require oxygen

24. 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
These processes all require oxygen

25. Think, Pair, Share
Compare and contrast isotonic and isometric exercises, and provide an example of each
Compare and contrast resistance and aerobic exercise, and provide an example of each
Why is exercise necessary for our muscles?
How does exercise help our body function?
These processes all require oxygen

26. Closure
What were our objectives today? What did you learn about these objectives? How does what we learned today tie to our unit question?
These processes all require oxygen

27. Critical Thinking 2 – Exit Ticket
The graph below indicates the amount of lactic acid produced by muscle cells as a function running pace.
Describe the data.
Explain
the data using
your
knowledge
of energy
systems and
exercise
These processes all require oxygen