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. Muscular Fatigue Mechanisms
What is Fatigue?
Muscular Fatigue Mechanisms

3. VCE Physical Education - Unit 3
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.
Our response to fatigue depends on;
The type, intensity and duration of the activity
The fitness level and mental state of the performer.
The muscle fibre being used
Types of muscular contraction occurring
The amount of metabolic by products being produced
The athlete’s hydration levels
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4. Muscle Fibre Type and Fatigue
Fast Twitch Fibres - Fast reaction time which relies on PC stores.
Unfortunately these stores deplete quickly.
Fast twitch also have a reduced oxygen supply in comparison to the aerobic slow twitch fibres.
Slow Twitch – High stores of glycogen and triglycerides helps produce energy for endurance activities.
Eventually fuel reserves are depleted or the neuromuscular process breaks down.
See fig 6.2 and 6.3 p
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5. VCE Physical Education - Unit 3

6. Muscular Contraction Types
Muscle Contraction
Muscular Action
Examples
Isotonic
Muscle length changes throughout range of movement. There are two types of isotonic contractions;
Concentric – Shortening of muscle while force is developed
Eccentric – Lengthening of muscle while force is developed
Push ups
Sit ups
Throwing
Kicking
Most sports
Isometric
No change in muscle length while force is developed. However this training method causes an increase in blood pressure.
Pushing against wall
Holding a bat
Isokinetic
High-speed contraction through full range of motion. Needs specialist training equipment
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Types of fatigue
General
Fatigue in all muscles groups
Eg. After completing full weights session
Chronic
Unhealthy level of fatigue, caused by breakdown of body’s defences.
Eg. Chronic fatigue syndrome
Local
Fatigue in specific muscle group
Eg. Biceps during bicep curls
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8. VCE Physical Education - Unit 3
Levels of Fatigue
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9. Muscular Fatigue Mechanisms
Causes of Fatigue
Muscular Fatigue Mechanisms

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Causes of Fatigue
A number of processes cause muscular fatigue including;
Energy Systems used
Depleted fuel stores (Glycogen / PC and other phosphate compounds)
Metabolic by-products
Reduced ability to extract energy
Increased body temperature
Dehydration
Changes in blood flow
VCE Physical Education - Unit 3

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

12. Muscular Fatigue Mechanisms
Depletion of Fuels
Muscular Fatigue Mechanisms

13. VCE Physical Education - Unit 3
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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15. 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 (Greater than an hour); 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.
Low Energy Stores
Athletes should follow strict diets when preparing for events so that fatigue is minimised or delayed.
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16. Anaerobic Pathway & Fatigue
Anaerobic Exercise
Energy supplied by Phosphate Creatine (1-15 sec) and anaerobic glycolysis (15sec-2min).
Oxygen deficit occurs.
Fatigue caused by lactic acid accumulation, which inhibits muscular contractions (Prevents calcium ion flow to myosin filament).
Lactic acid also prevents enzymes breaking down glucose stores
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18. Metabolic By-Products
Muscular Fatigue Mechanisms

19. 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.
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 lactate and hydrogen ions during physical activity.
These by-products effect;
Contraction of myosin, disruption to the work of enzymes, the neuromuscular junction, ionic concentrations.
Summary See fig 6.7 p.136
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20. By-products - Accumulation of LA
Lactic acid – Produced as a result of pyruvic acid reacting in the absence of oxygen.
As the rate of anaerobic glycolysis increases, lactic acid accumulates.
It effects the ability of energy extracting enzymes to work effectively.
It also lowers the blood’s pH levels.
Lactic acid eventually reaches maximum levels within both the muscle fibres and in the blood (Lactate threshold).
Fatigue results as the accumulated lactic acid inhibits muscular contractions.
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21. How LA affects muscular contractions
Inhibiting the secretion of calcium ions that enable the coupling of the actin and myosin protein filaments. Protein filaments cannot attach to each other. The sliding of filaments is not possible.
Inhibiting the action of the glycolytic enzymes resulting in glucose not being broken down.
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22. By-Product 2 - Accumulation of H+ ions
Another by-product of anaerobic glycolysis.
Accumulation of H+ ions within the working muscle and blood plasma results in the levels of pH of the cell decreasing to an extent where muscle contraction is no longer possible and fatigue occurs.
The low pH created by the H+ ions causes the glycolytic enzymes to become inoperative. Without the glycolytic enzymes, the breakdown of glucose cannot take place.
Inorganic phosphate (Pi) can also have a similar fatiguing effect on the body.
VCE Physical Education - Unit 3

23. The Redistribution of Blood Flow
Muscular Fatigue Mechanisms

24. Redistribution of Blood Flow
p.138
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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26. Muscular Fatigue Mechanisms
Dehydration
Muscular Fatigue Mechanisms

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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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Dehydration
Sweating is the body’s natural process for regulating body temperature during exercise.
As an athlete’s core temperature increases so does the rate of sweat production.
Sweat contains electrolytes, salts and water, and dehydration is the loss of this body fluid. Varying rates of sweat, work, fluid intake and individual physiological characteristics all contribute to the level of dehydration that may be experienced.
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Dehydration
p.141
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,
Fluid loss can be prevented by;
Drinking water prior, during and after events.
Use sports drinks for extended activities
Use a fluid replacement routine
Avoid being dehydrated before sport
Written Report p.140
Case Study p.141
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30. Dehydration continued
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

31. 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.
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32. 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