1. Muscle Fatigue

2. What causes Muscle Fatigue?
Muscle fatigue is a multiplication of factors that lead to decreased physical activity
Three things contribute to Muscle Fatigue
Phosphagen/ Lactic Acid system
Delayed On-set Muscle Soreness
Biomolecules use to supply energy

3. Phosphagen System
Body has some ATP within the body, readily available to muscles for work
Supply energy needs of working muscle at
Only for ~10 seconds
Body turns to the Phosphagen System first
Involves Creatine Phosphate and Creatine Kinase
Short bursts of activity – sprinting
Body relies on this pathway

4. Phosphagen System
To replenish the ATP levels quickly, muscle cells use Creatine Phosphate
High energy phosphate
Enzyme that removes phosphate from C.P. is Creatine Kinase
Transfers phosphate from C.P. to ADP  ATP
Reaction is reversible
re-form Creatine Phosphate to generate more ATP

5. Lactic Acid System
Phosphagen system does not depend much on glucose reserves
When activity continues for longer periods of time, body shifts to Lactic Acid Fermentation
Involves more chemical reactions than the Phosphogen system
Longer time to generate ATP
Still Rapid enough to produce ATP to last ~90 sec
Produces Lactic Acid as a by product
Cause soreness, lead to fatigue later

6. Aerobic Respiration
After ~2 min. of exercise, body shifts to Aerobic respiration
Breakdown of gluose…
Glucose can come from various places
glycogen supplies in muscle & liver, direct absorption from food in small intestine
If stores of glucose are finished, body can turn to fatty acids, then proteins
Aerobic respiration takes longer than Phosphogen or Lactic acid – but can supply energy for a longer time

7. In Order, now Start by using free ATP in cells
Lasts for less than 5 sec.
Next, Phosphagen pathway kicks in
Supplies energy for 8 to 10 seconds
Involved in rapid acceleration, short-duration exercise
If continues, lactic acid pathway starts
Builds up Lactic Acid in muscles, causes secondary effect of pain
short-distance exercises
Finally, aerobic respiration
Generate large amounts of ATP
Occur in endurance events

8. Delayed-Onset Muscle Soreness
Every time you exercise you are breaking muscle fibers
This is normal
Breaking down sites where muscle contraction occurs
Muscle rebuilds connections, stronger
If wait time is not long enough, soreness develops
Lactic acid contributes to muscle soreness as well
L.A. is what makes your muscles hurt post work-out
Lactic acid builds up in the muscle tissue
Causes the fatigue and soreness
Both result in lower muscular output

9. How do we tie the animation to what we know?

10.  Exertion Requires  in ATP
Sec. 0 – 3
ATP need comes from stores w/in cells
Sec. 3 – 10
ATP need comes from Phosphagen System
Creatine Kinase removes phosphate from Creatine Phosphate - forms ATP
< 90 – 120 s.
ATP forms from Lactic Acid Fermentation
Significantly less ATP/glucose (2/1)
Leads to fatigue and pain
Lactic Acid interferes w/ muscle contraction

11. >2 min.
ATP formed from Aerobic Respiration IF person is AEROBIC CAPACITY
Aerobic Capacity – when pyruvates are formed from glycolysis at a rate matched by O2 delivery
Aerobic Capacity can be sustained for a long time, depending on your level of conditioning.
Factors that affect Aerobic Capacity
Heart rate stroke volume
Amount of capillaries in body
Level of hemoglobin
Amount of stored glycogen
Lung capacity

12. What if we wanted to condition in order to burn body fat?
What happens when you are running at aerobic capacity and you reach a hill or are pushed by a competitor?
Push harder, more effort
Body moves over aerobic capacity
Compensate by doing more anaerobic respiration
What if we wanted to condition in order to burn body fat?
Must exercise long enough to lower glycogen stores so body turns to lipids
Body requires 4x O2 supply to metabolize fat than carbs.
Need low intensity over long periods of time AND have low heart rate

13. How can we metabolically use fats and proteins?

14. Carbohydrate Any carbohydrate digested will be converted into glucose
Very easily broken down
Matter of time needed for digestion & absorption
Polysaccharide & Disaccharides digested into monosaccharide in digestive tract
All monosaccharide are absorbed in liver – converted to glucose or glycogen

15. Fats When fats are digested Majority of energy is in the fatty acids
Broken down into glycerols and fatty acids (triglycerides)
Glycerol is converted to an intermediate & used in Glycolysis
Majority of energy is in the fatty acids
Break down fatty acid chain into 2-carbon molecule fragments
– 14 – 12…
Process named β Oxidation
2-Carbon attaches to CoA
Makes Acetyl CoA
New Acetyl CoA mol. enter Krebs Cycle
Only can be processed Aerobically
Think about working out…

16. Fats Huge amount of energy
Fat has more energy in bonds than other biomolecule
Each 2-carbon chain is converted into an Acetyl CoA
For example –
A 18-carbon fatty acid can produce 9 Acetyl Co-A
Can make 190 ATP from a 18-C Fatty Acid tail!!!!!!
Huge amount of energy

17. Proteins Then, must be Deaminated – amino groups must be removed
Proteins can also be used for fuel
First – digestive enzymes break proteins into amino acids
Amino acids can enter cycle to build biomolecules
New amino acids
Essential Amino Acids
Then, must be Deaminated – amino groups must be removed
Nitrogen is further processed as waste products – urea

18. Proteins Incoming Krebs Cycle molecules can also…
Enzymes then convert proteins into intermediates of Glycolysis and the Krebs cycle
Can make Acetyl CoA
Can make other 4-5 C structures
Pyruvate
Other structures used in Krebs Cycle
Incoming Krebs Cycle molecules can also…
Provides building blocks for biosynthesis of every other organic compounds the organism needs
Essential amino acids, vitamins, minerals, fatty acids all involved in pathway

19. When fat reserves are diminished,
Protein from body tissue will supply metabolic needs
For all cells and tissues
Body will degrade itself to maintain metabolic activity
When starving, fasting or when there is insufficient carbohydrate/lipids for energy needs…
Body uses proteins from body tissues to supply fuel molecules to the brain, nerve cells and red blood cells
These cells have the highest energy requirement of all cell types