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Muscular Fatigue Mechanisms


Chapter 6 Muscular Fatigue Mechanisms Text Sources Nelson Physical Education VCE Units 3&4: 4th Edition Malpeli, Horton, Davey and Telford 2006. – PowerPoint PPT presentation

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Title: Muscular Fatigue Mechanisms

Chapter 6
  • Muscular Fatigue Mechanisms
  • Text Sources
  • Nelson Physical Education VCE Units 34 4th
    Edition Malpeli, Horton, Davey and Telford
  • 2. Live It Up 2 2nd Edition Smyth, Brown,
    Judge, McCallum and Pritchard 2006.

What is Fatigue?
  • Muscular Fatigue Mechanisms

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
  • Exercise increases the physiological effects of
  • Our response to fatigue depends on
  • The type, intensity and duration of the activity
  • The fitness level and mental state of the
  • The muscle fibre being used
  • Types of muscular contraction occurring
  • The amount of metabolic by products being
  • The athletes hydration levels

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
  • Eventually fuel reserves are depleted or the
    neuromuscular process breaks down.
  • See fig 6.2 and 6.3 p.132-133

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Muscular Contraction Types
Types of fatigue
  • General
  • Fatigue in all muscles groups
  • Eg. After completing full weights session
  • Chronic
  • Unhealthy level of fatigue, caused by breakdown
    of bodys defences.
  • Eg. Chronic fatigue syndrome
  • Local
  • Fatigue in specific muscle group
  • Eg. Biceps during bicep curls

Levels of Fatigue
Causes of Fatigue
  • Muscular Fatigue Mechanisms

Causes of Fatigue
  • A number of processes cause muscular fatigue
  • 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

Causes of Fatigue
Body Temperature
Metabolic By-products (LA, H, Pi, Creatine)
Energy pathways
Fuel stores (PC and glycogen)
Hydration levels
Blood flow redistribution
Depletion of Fuels
  • Muscular Fatigue Mechanisms

Fuel Depletion
  • Most commonly exhausted energy stores are PC and
  • 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 conversion to energy is far less efficient
    than that for glycogen, resulting in a reduced
  • As energy stores are continually depleted,
    fatigue occurs and therefore the quality of
    performance decreases

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Aerobic Pathway Fatigue
  • Aerobic Exercise
  • Less than 20 minutes
  • No major fatigue and carbos 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.

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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Metabolic By-Products
  • Muscular Fatigue Mechanisms

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
  • Summary See fig 6.7 p.136

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 bloods 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.

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.

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
  • 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.

The Redistribution of Blood Flow
  • Muscular Fatigue Mechanisms

Redistribution of Blood Flow
  • 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
  • The body therefore needs to monitor its balance
    between cooling and muscle supply
  • 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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  • Muscular Fatigue Mechanisms

  • 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.
  • 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

  • Sweating is the bodys natural process for
    regulating body temperature during exercise.
  • As an athletes 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.

  • 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

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 10-20 .
  • 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.

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 30-60 mins prior to the game.
  • Drink at least 200 mL of water every 15mins
  • Weighing yourself before and after sport is a
    good way to assess fluid levels.
  • One kilogram of weight lost one litre of fluid
  • After participating, aim to replace more than the
    fluid lost as sweating and fluid loss continues
    after exercise.

Web Links Chapter 6
  • Nicholas Institute of Sports Medicine and
    Athletic Trauma exercise physiology
  • Information on skeletal muscles in the human
    body http//
  • Sport science (site for sports research)
  • Anaerobic management (training and recovery)
  • Biophysical journal online http//www.biophysj.or
  • PubMed (includes links to full text articles and
    other related resources) http//
  • Article Unravelling the Process of Muscle
    Fatigue http//
  • Physiology online magazine (American
    Physiological Society) http//
  • Science-a-go-go (science news, research and
    discussion) http//
  • University of Western Australia, physiology
    department http//
  • Innovations Report Forum for science,
    industry and business http//www.innovations-