1. VCE Physical Education - Unit 3
Chapter 6
Muscular Fatigue Mechanisms
Text Sources
Nelson Physical Education VCE Units 3&4: 4th Edition – Malpeli, Horton, Davey and Telford 2006.
2. Live It Up 2: 2nd Edition – Smyth, Brown, Judge, McCallum and Pritchard 2006.
VCE Physical Education - Unit 3

2. Types of fatigue Fatigue Description Example Local
Fatigue in specific muscle group
Biceps during bicep curls
Quads in snowboarding
General
Fatigue in all muscles groups
After completing full weights session
Playing a full game of football etc.
Chronic
Unhealthy level of fatigue, caused by breakdown of body’s defences.
Chronic fatigue syndrome
Overtraining
Reoccurring illness or injuries
VCE Physical Education - Unit 3

3. Muscular Fatigue Mechanisms
What is Fatigue?
Muscular Fatigue Mechanisms

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What is Fatigue?
Fatigue occurs when the body is unable to function at its optimal level. The muscles are unable to exert maximal force levels as a result of exercise.
Fatigue occurs through everyday physical activity.
Exercise increases the physiological effects of fatigue.
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5. Muscular Fatigue Mechanisms
Causes of Fatigue
Muscular Fatigue Mechanisms

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Causes of Fatigue
Our response to fatigue depends on;
1. The muscle fibre being used
2. Types of muscular contraction occurring
3. Depleted fuel stores (Glycogen / PC and other phosphate compounds)
4. Energy Systems used and the ability to extract energy
5. The amount of metabolic by products being produced
6. Changes in blood flow and increased body temperature
7. The athlete’s hydration levels
A number of underlying processes that also determine the level of muscular fatigue include;
The type, intensity and duration of the activity
The fitness level and mental state of the performer.
VCE Physical Education - Unit 3

7. Causes of Fatigue Body Temperature
Metabolic By-products (LA, H+, Pi, Creatine)
Energy pathways
Fuel stores (PC and glycogen)
Hydration levels
Blood flow & redistribution

8. VCE Physical Education - Unit 3
Checkpoints
Complete questions 1-4 page 134 of Nelson Physical Education VCE Units 3 & 4.
VCE Physical Education - Unit 3

9. Muscular Fatigue Mechanisms
1. Muscle Fibre Types
Muscular Fatigue Mechanisms

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Muscle Fibres
Muscle fibre types can be broken down into two main types:
Slow twitch (Type I) muscle fibres and
Fast twitch (Type II) muscle fibres [Contains Type II a and b]
Human muscles contain a genetically determined mixture of both slow and fast fibre types.
On average, we have about 50% slow and 50% fast fibres in most of the muscles used for movement.
Slow Twitch (Type I) The slow muscles contain more mitochondria and myoglobin which make them more efficient at using oxygen to generate more fuel (ATP) for continuous, extended muscle contractions over a long time.
Fast Twitch (Type II) Because fast twitch fibres use anaerobic metabolism to create fuel, they are much better at generating short bursts of strength or speed but fatigue more quickly.
Fast twitch fibres are able to fire more rapidly than slow twitch, hence their name.
The slow twitch fibres, on the other hand, fire more slowly, but can go for a long time before they fatigue.
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11. VCE Physical Education - Unit 3
Muscle Fibre Type Summary
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13. 2. Muscle Contraction Types
Muscular Fatigue Mechanisms

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Contraction Types
Isotonic Isometric Isokinetic
Muscle Lengthens No change in length Contraction through full range of motion
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15. Muscular Fatigue Mechanisms
3. Depletion of Fuels
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Fuel Depletion
Most commonly exhausted energy stores are PC and glycogen.
Stores of glycogen in the muscle and liver can fuel continuous exercise for over 90 mins.
Muscle glycogen is generally the first fuel source used during aerobic exercise; then liver glycogen and eventually blood-borne and stored fat.
Fat conversion to energy is far less efficient than that for glycogen, resulting in a reduced intensity.
As energy stores are continually depleted, fatigue occurs and therefore the quality of performance decreases
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17. VCE Physical Education - Unit 3

18. Muscular Fatigue Mechanisms
4. Energy Systems
Muscular Fatigue Mechanisms

19. 4. Aerobic Pathway & Fatigue
Aerobic Exercise
Less than 20 minutes;
No major fatigue and carbo’s and fats used as energy (Very little lactic acid).
Extended activities (Several hours of constant exercise);
Fats used as fuel therefore body must slow down (More oxygen required).
Fatigue caused by depleted fuel stores, dehydration, increased body temp, physical and mental stress.
Anaerobic Exercise
Energy supplied by ATP-PC (1-15 sec) and anaerobic glycolysis (15sec-2min).
Energy Stores
Athletes should follow strict diets when preparing for events so that fatigue is minimised or delayed.
Elite athletes have nutritional programs to aid their performance and recovery.
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20. VCE Physical Education - Unit 3
Summary Table
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21. 5. Metabolic By-Products
Muscular Fatigue Mechanisms

22. Metabolic by-products
Metabolic by-products are compounds made as a result of chemical reactions within the body. They are the ‘left-overs’ as such.
Eg. When making ATP using phosphocreatine, the by-product is creatine:
ADP + PC ATP + creatine
By-products can prove harmful to the body by causing it to function in a less efficient way, such as through the effect of hydrogen ions during physical activity.
These by-products effect the functioning of the working muscle
eg. Ability to break down glycogen, ability to send signals to the muscle and the changing concentration of minerals in and around the muscle.
Summary See fig 6.7 p.136 for ATP production
during muscular activity.
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23. Current Investigations
The role of intracellular metabolites in controlling membrane excitability and the release of intracellular calcium during fatiguing exercise are now hotly being investigated - Pi, Ca2+, Na+ and K+.
The hydrogen ion theory as a major fatiguing product is hotly debated at present.
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24. Lactic Acid – The Myths Busted
Lactic acid has a bad reputation. Many people blame it for fatigue, sore muscles, and cramps.
Scientists have discovered that lactic acid plays a critical role in generating energy during exercise.
When your body makes lactic acid, it splits into lactate ion (lactate) and hydrogen ion.
The lactate ion provides fuels for many tissues, helps use dietary carbohydrates, and serves as fuel for liver production of glucose and glycogen.
However, lactic acid does have a dark side.
The Hydrogen ion is the acid in lactic acid.
It interferes with electrical signals in your muscles and nerves, slows energy reactions, and impairs muscle contractions.
The burn you feel in intense exercise is caused by hydrogen ion build-up.
Inorganic phosphate (Pi) can also have a similar fatiguing effect on the body.
So, when you fatigue, don't blame it on lactic acid. Rather, place the blame where it belongs- on hydrogen ion.
Lactic Acid
VCE Physical Education - Unit 3

25. Lactate Inflection Point (LIP)
The relationship between blood lactate levels and anaerobic metabolism is still unclear. The term anaerobic threshold (AT) is therefore no longer used in the field exercise physiology and this area of study due to its conflicting meaning.
The preferred term, lactate inflection point (LIP), is the point where blood lactate levels increase, as a direct result of increasing exercise intensity.
Exercise intensities beyond the LIP causes fatigue due to a reliance on anaerobic pathways to supply ATP and the build up of the metabolic by-products.
LIP can be measured in the laboratory using blood analysis or ventilation measurements. It is a good measure of an athletes speed and power of an athlete over a prolonged period. It can also distinguish between middle and long distance runners during a VO2 max test.
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26. VCE Physical Education - Unit 3
L.I.P
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27. VCE Physical Education - Unit 3
Checkpoints
Complete questions 1-5 page 137 of Nelson Physical Education VCE Units 3 & 4.
VCE Physical Education - Unit 3

28. 6. The Redistribution of Blood Flow
Muscular Fatigue Mechanisms

29. Blood Flow and Body Temperature
During exercise;
Increased demand for oxygen
Increased waste products
Increased blood volume to working muscles
Increased cardiac output
Less blood flow to vital organs and more to the working muscles
This can cause an increase in core body temperature.
The body therefore needs to monitor its balance between cooling and muscle supply (Thermoregulation)
Body Temperature Increase
Due to blood being brought to the surface (vasodilation of veins) of the skin (cooling mechanism), less blood is supplied to the working muscles. This lessens the ability to produce ATP and lactic may be produced.
See fig 6.2 p.138 and 6.8 p.139
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30. Redistribution of Blood Flow
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31. VCE Physical Education - Unit 3
Checkpoints
Complete questions 1-2 page 138 of Nelson Physical Education VCE Units 3 & 4.
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32. Muscular Fatigue Mechanisms
7. Dehydration
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Dehydration
Sweating causes;
A loss of salt, electrolytes and water.
This can cause;
Impaired coordination, decision making and endurance levels.
An impact on the cardiovascular system
A rise in body temperature
Levels of dehydration are affected by;
Duration and intensity of session
Environmental conditions and acclimatisation.
The individual physiological characteristics
Fluid intake
Athletes can become dehydrated due to;
Not having access to fluids during competition
Not tolerating drinking while exercising
Inability to match intake with loss of fluids
If dehydrated, athletes are more prone to; Cramp, heat stress and heat stroke, poor performances and increase the risk of injury.
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34. VCE Physical Education - Unit 3
Dehydration
Signs of dehydration;
Mild to severe thirst
Rapid loss in weight (1 kg of weight lost = 1L of sweat lost).
Dry lips and tongue, confusion
Decreased urine volume
Dark urine
Increased breathing rate
Light headedness nausea and headache
Confusion, nausea, headache
faster breathing rate than normal
Combination of dehydration and electrolyte loss can make the athlete more susceptible to cramp, heat stress and heat stroke.
A loss of 2% of body weight (just 1 kg for a 50-kg person) causes an increase in perceived effort and could reduce performance by %.
Loss exceeding 3-5% of body weight reduces aerobic exercise performance noticeably and impairs reaction time, judgment, concentration, cognitive abilities and decision making.
Complete hydration is vital for achieving optimal performance and minimising the negative effects of fatigue.
VCE Physical Education - Unit 3

35. Guidelines for Reducing Dehydration
Do not wait until you are thirsty - thirst is a poor indicator of hydration levels.
Drink cool water - absorbed more rapidly
Use a sports drink if exercise is 1 hour +.
Avoid starting exercise dehydrated.
500 mL of water mins prior to the game.
Drink at least 200 mL of water every 15mins during
Weighing yourself before and after sport is a good way to assess fluid levels.
One kilogram of weight lost = one litre of fluid lost.
After participating, aim to replace more than the fluid lost as sweating and fluid loss continues after exercise.
VCE Physical Education - Unit 3

36. VCE Physical Education - Unit 3
Coursework 6.1 and 6.2
Complete the written report task on page 140 of Nelson Physical Education VCE Units 3 & 4.
Complete the case study on page 141 of Nelson Physical Education VCE Units 3 & 4.
VCE Physical Education - Unit 3

37. VCE Physical Education - Unit 3
Checkpoints
Complete questions 1-9 page 141 of Nelson Physical Education VCE Units 3 & 4.
VCE Physical Education - Unit 3

38. Fatigue and Energy Systems
Predominant
energy system
Likely causes of fatigue
Types of recovery
ATP/PC
Fuel Depletion:
ATP & PC
Rest recovery
Lactic Acid
Accumulation of metabolic by-products:
H+ (hydrogen ions)
Pi (inorganic phosphates)
NB – Lactic Acid is no longer thought to contribute to fatigue. In fact, it is being regarded more as a positive performance enhancer rather than a negative
Non-dietary
Active Recovery
Massage
Hydro/water based therapies
e.g. contrasting via hot/cold baths
Aerobic
Glycogen stores, then fats
Elevated body temperature leading to:
Dehydration
Blood flow away from muscles
Dietary
High GI foods
Rehydration via sports drinks:
Hypertonic to replace glycogen
Hypotonic to replace lost fluids
VCE Physical Education - Unit 3

39. VCE Physical Education - Unit 3
Test Your Knowledge
Complete the review questions 1-4 page of Nelson Physical Education VCE Units 3 & 4.
VCE Physical Education - Unit 3

40. VCE Physical Education - Unit 3
Peak Performance
Complete the chapter questions on page of Nelson Peak Performance Physical Education VCE Units 3 & 4.
VCE Physical Education - Unit 3

41. VCE Physical Education - Unit 3
PHYS ED Notes
Read the summarised information of pages of PHYS ED Notes and complete the revision questions.
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42. VCE Physical Education - Unit 3
Web Links – Chapter 6
Nicholas Institute of Sports Medicine and Athletic Trauma – exercise physiology:
Information on skeletal muscles in the human body:
Sport science (site for sports research):
Anaerobic management (training and recovery):
Biophysical journal online:
PubMed (includes links to full text articles and other related resources):
Article – Unravelling the Process of Muscle Fatigue:
Physiology online magazine (American Physiological Society):
Science-a-go-go (science news, research and discussion):
University of Western Australia, physiology department:
Innovations Report – Forum for science, industry and business: report.com
Australian Sports Commission:
Find 30 promotion (Government of WA Department of Health):
Walking School Bus promotion (UK):
Ministry of Health (New Zealand) toolkits:
The 10,000 Steps Rockhampton project:
Travelsmart Australia:
World Health Organisation:
Heart Foundation Australia:
VicHealth (The Victorian Health Promotion Foundation):
Be Active promotion (Government of South Australia):
Go For Your Life:
Physical Activity Resources for Health Professionals – Introduction (Centre for disease control and prevention – USA):
Health Promotion (Public Health Agency of Canada):
Strategic Inter-Governmental Forum on Physical Activity and Health (SIGPAH):
Healthy youth (Centre for disease control and prevention (USA):
America On The Move promotion:
Papers from the International Journal of Behavioural Nutrition and Physical Activity:
Department of health and aging (Australian government):
Building a healthy, active Australia (Australian government):
National Public Health Partnership:
Sport and Recreation Australia:
VCE Physical Education - Unit 3