1. The document discusses various mechanisms of muscular fatigue, including fuel depletion, accumulation of metabolic by-products like lactic acid, and elevated body temperature. 2. It explains how different types of exercise and energy systems used can lead to different types and onset of fatigue. High intensity anaerobic exercise can cause faster fatigue due to reliance on anaerobic pathways. 3. Recovery is important to reverse fatigue and prepare for future exercise. Different recovery strategies should be used depending on the predominant energy system and causes of fatigue.

1.  Sian Welch & Wendy
Ingraham - The Crawl -
1997
VCE Physical Education - Unit 3

2. Muscular Fatigue Mechanisms

3. Fatigue is the exercise induced reduction in the power
generating capacity of a muscle and an inability to
continue the activity.
As fatigue sets in, force in your muscles reduces,
muscle responses to brain stimuli reduces and activity
levels decrease.
VCE Physical Education - Unit 3

4.  When and how fast fatigue kicks in is dependant
upon the following:
◦ Type of activity (intermittent/continuous)
◦ Muscle fibre type used (slow/fast twitch. Slow=longer)
◦ Type of muscle contraction (isotonic/isometric-
fastest/isokinetic)
◦ Intensity and duration of activity (high
intensity/anaerobic= quicker fatigue)
◦ Level of fitness
VCE Physical Education - Unit 3

5. Fatigue Causes, signs & symptoms Example
Local Fatigue is experienced in a muscle or group of Biceps during bicep
muscles localised in part of the body. This tends to curls
occur if the same muscle group is called upon
repeatedly during training (without sufficient
recovery) or performance. Muscles often experience Quads in
a heaviness, tingling pain or cramp-like feelings. snowboarding
General This tends to occur after completing a full training After completing full
session or competitive game of football, netball or weights session
the like. Performers feel that all their muscles are
‘weakened’
and sometimes also experience psychological Playing a full game of
fatigue as well. football etc.
Chronic Performers experience an unhealthy breakdown of Chronic fatigue
their immune system. This is usually caused by syndrome
overtraining as a result of poor training program
design, inappropriate recovery strategies and/or
Overtraining
excessive competition demands or schedules.
Chronic fatigue is dangerous and is often
accompanied by increased susceptibility to illness Reoccurring illness or
or infections, persistent muscle soreness and injuries
reduced motivation levels.
VCE Physical Education - Unit 3

6. Muscular Fatigue Mechanisms

7. Fatigue mechanisms have been found to be multifactorial. Factors
that help determine when performance will deteriorate include:
1. Exercise type, duration and intensity
2. Types of muscular contractions
3. Physical fitness or conditioning
4. Age
5. Diet
6. Environmental factors
7. Mental state of the performer
VCE Physical Education - Unit 3

8. Fuel depletion Metabolic by- Neuromuscular Elevated body
products events temperature
•Intramuscular • Hydrogen ions • Decreased • Very high core
ATP (H+) in plasma ‘firing’ of the temperatures
• and muscle central nervous • Increased rates
Phosphocreatine • Inorganic system of dehydration
(PC) phosphate (Pi) • Impaired • Redistribution
• Muscle • Adenosine sodium (Na+) of blood to assist
glycogen diphosphate and potassium cooling
• Blood glucose (ADP) (K+) gradients
• Calcium ions
(Ca2+)
VCE Physical Education - Unit 3

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

10. Lactic acid has a bad However, lactic acid does have
reputation. Many people a dark side.
blame it for fatigue, sore  The Hydrogen ion is the acid
muscles, and cramps. in lactic acid.
 Scientists have discovered  It interferes with electrical
that lactic acid plays a critical signals in your muscles and
role in generating energy nerves, slows energy
during exercise. reactions, and impairs muscle
 When your body makes lactic contractions.
acid, it splits into lactate ion  The burn you feel in intense
(lactate) and hydrogen ion. exercise is caused by
 The lactate ion provides fuels hydrogen ion build-up.
for many tissues, helps use  Inorganic phosphate (Pi) can
dietary carbohydrates, and also have a similar fatiguing
serves as fuel for liver effect on the body.
production of glucose and  So, when you fatigue, don't
glycogen. blame it on lactic acid.
Rather, place the blame
where it belongs- on
hydrogen ion.
Lactic Acid
VCE Physical Education - Unit 3

11.  Lactate inflection point (LIP), is  LIP can be measured in the
the point where blood lactate laboratory using blood analysis
levels increase, as a direct result or ventilation measurements. It
of increasing exercise intensity. is a good measure of an
athletes speed and power of
 Exercise intensities beyond the an athlete over a prolonged
LIP causes fatigue due to a period. It can also distinguish
reliance on anaerobic pathways between middle and long
to supply ATP and the build up distance runners during a VO 2
of the metabolic by-products. max test.
 LIP is usually triggered above
85% of a persons maximum
heart rate.
 When lactate accumulates and
severe blood acidosis occurs
(high levels of hydrogen ions
and acidity), fatigue follows
quickly.
VCE Physical Education - Unit 3

12.  Oxygen deficit occurs
at the beginning of
exercise when
oxygen demand is
greater than oxygen
supply.
 When the body has
an oxygen deficit,
ATP is sourced from
the anaerobic
systems.
 See graph page 152
VCE Physical Education - Unit 3

13. Oxygen Debt (EPOC) Excess Post-
exercise Oxygen Consumption
•Oxygen debt is defined as the volume of oxygen used during
recovery from exercise in excess of resting oxygen consumption.
•Occurs after anaerobic exercise.
•Divided into 2 parts. 1(fast)- restores PC in approximately 2-3
minutes. 2-3 litres of oxygen is consumed to provide this
resynthesisation. 2 (slow)-removes lactic acid through buffering.
Recovery depends on usage and metabolic disturbances during
activity.
•High intensity activities = a large oxygen deficit, small (or no)
steady state, large oxygen deficit/EPOC
•Low intensity activities = a small oxygen deficit, long steady state,
small oxygen debt/EPOC
VCE Physical Education - Unit 3

14.  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
VCE Physical Education - Unit 3

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

16. Muscular Fatigue Mechanisms

17. 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.
VCE Physical Education - Unit 3

18. Muscular Fatigue Mechanisms

19. Aerobic Exercise Energy Stores
Less than 20 minutes; Athletes should follow strict diets
 No major fatigue and carbo’s when preparing for events so
and fats used as energy (Very that fatigue is minimised or
little lactic acid). delayed.
Extended activities (Several hours of  Elite athletes have nutritional
constant exercise); programs to aid their
 Fats used as fuel therefore performance and recovery.
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).
VCE Physical Education - Unit 3

20.  Recovery is used to return the body to pre-
exercise conditions and therefore reverse the
effects of fatigue.
 Efficient recovery enhances adaptations to
exercise loads and prepares the performer for
future training/competition
 Inefficient recovery delays the removal of
fatiguing factors and can lead to injuries and
over training.
 Exercisers need to ensure they match their
recovery to the causes of fatigue
VCE Physical Education - Unit 3

21. VCE Physical Education - Unit 3

22. VCE Physical Education - Unit 3

23. Complete review
questions on page
171-172
VCE Physical Education - Unit 3