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 When
food is digested, energy is released.
 The amount of energy released from each
food is measured in kilojoules (KJ)
 The body breaks down the food into 3
sources of fuels and each provides different
amounts of energy
1. FATS – 38kj per gram
2. CHOs – 17kj per gram
3. PROTEIN – 17kj per gram
Energy required depends on: age, sex, body
size and activity level
Carbohydrates (CHO)
Preferred source of fuel
during exercise (Glycogen)
Fat
Concentrated fuel used
during rest and prolonged
sub-maximal exercise.
Protein
Used for growth and repair
(Negligible use during
exercise)
Using Table 5.1 of your text book, complete the following table into your
workbooks
Food Fuel
CHO’s
FATS
PROTEIN
RDI for a
balanced diet
Food Fuel after
conversion/
digestion
Storage
 Foods
rich in CHO play a vital role in exercise
performance because they are the most
readily available source of energy to fuel
working muscles.
 Digestion breaks CHO into glucose for energy
which is absorbed by the bloodstream, if the
body does not require energy immediately
the glucose is stored in glycogen in the liver
and muscles.
 Any excess CHO are stored as fats
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Can predominantly supply energy for high
intensity short duration activities such as 200m
sprints but also supply energy for sub-maximal
longer duration activities such as a 5km jog.
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THEREFORE the body uses glycogen as its major
fuel during exercise and CHO as a fuel can last
up to 90 minutes of continuous activity.

The athlete needs to continually top up CHO
stores to ensure there is enough in the muscles
before the start of training and competition.
Storage (Based on 80kg person)
 Muscle glycogen – 400g
 Liver glycogen – 100g
Intake of Carbohydrates
depends on the intensity and
duration of exercise bouts.
 Normal contribution to diet
is 55-60% CHO
 Carbohydrate loading (7-12g
CHO / kgBM) is used to
prevent depletion of
glycogen in endurance
activities.
VCE Physical Education - Unit 3
Carbohydrate rich diet;
 Increases glycogen stores
 Glycogen is used in rebuilding
ATP
CHO preferred fuel over fats
during exercise due to
requiring less oxygen to
release energy.
Athletes need to be aware of
their dietary intakes of CHO.
Excess CHO is converted to
adipose tissue (Fat).
The Glycemic Index (high or low) is a ranking
for CHO that the rate at which glucose is
released into the bloodstream.
LOW GI: Glucose is
released slowly into the
bloodstream without the
corresponding increased
insulin release.
HIGH GI: Glucose is
released quickly into
the bloodstream. If at
rest, insulin will be
released to regulate
glucose levels.
 Insulin
is a substance released to regulate
blood glucose levels
 An
increase in blood glucose levels – caused
by consuming high GI foods – result in the
increase in insulin secretion which results in
increased glycogen metabolism (use)
 Ingesting
protein in recovery amplifies insulin
response increasing glycogen uptake
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Comes from muscle glycogen first, followed by liver glycogen
Varies according to the nature of the activity
CHO Loading – The practice of increasing CHO stores within the
muscles and body by increasing CHO intake and tapering
training in the time leading up to major competition (up to 10
days). As much as 80% of the athletes diet is CHO.
High intensity efforts via the anaerobic glycolysis system and
aids endurance performance via the aerobic energy system
Provides energy from PC restoration
During high intensity/short duration activities, CHO’s are the
primary energy source once PC has been depleted.
During moderate intensity/longer duration (aerobic energy
system) CHO’s and then fats are the sources of energy.
CHO’s are preferred over fats. WHY?

Events less than 1 hr in length require normal CHO reserves

Events lasting around 90 mins require well filled glycogen stores

Events 2 hrs or more require ‘super filled’ glycogen stores (CHO
loading)
QUESTIONS

Make a list of 5 events that would require an increase in CHO’s prior
to the event.

What types of foods should an athlete consume before, during and
after a marathon? Complete the following table.
Before Event
Food Fuel
Glycemic Index
During Event
Post Event
One glucose molecule
yields 36 – 38 ATP’s in
the presence of O2 but
only 2 to 3 ATP’s
without O2.

Fats are stored in the body in the form of triglycerides in fat
cells (adipose tissue) and in the skeletal muscle.

FFA the broken-down form of triglycerides provide energy for
sub-maximal exercise aerobically.
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Nutritionists recommended that fat make up 25- 30% of a
sporting diet.
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The transport of FFA to muscle fibres is slow and breakdown
requires O2, putting added stress on the O2 transport system

It is more difficult to use the energy from fat during exercise
however fats become increasingly important when the stores of
CHO are depleted during prolonged, continual physical activity.
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Trained athletes use fat as an energy source to a greater extent
than untrained athletes
Storage of fats
 Adipose tissue
 Triglycerides
(Broken down into free fatty
acids)
Aerobic metabolism of fat is;
 Slow
 Requires more oxygen
 Adds stress to the oxygen
transport system
 ATP yield is much higher
from fat (460 molecules) in
comparison to glucose (36).
VCE Physical Education - Unit 3
At rest
 50% of energy supplied by fats
 Oxygen demand is easily met
to burn fats
Benefits of fat
 Large energy store
 Transport medium for fat
soluble vitamins
Negative aspects of fat
 Obesity, heart disease etc.
 Fats
are mainly used to produce ATP when the
body is at rest – 2/3’s fuel source
 Also used as a fuel source during low intensity
exercise, but as the intensity of exercise
increases, the percentage of fat being used
decreases
 Fat breaks down into triglycerides which are
stored in the skeletal muscle or adipose tissue.
 Fat transported in the blood in the form of FFA
 Muscle triglycerides are predominantly used for
exercise of long duration where FFA are used
earlier (aerobically) to spare glycogen stores.
 Has
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several important functions in the body
Formation and growth of body, tissues, especially muscle
tissue and cells
Repair and recovery of damaged tissues
Production of RBC, hormones & enzymes (speed up
chemical reactions).
Provision of emergency fuel source during exercise when
CHO and fat stores are depleted
 Protein
is broken down through digestion into
amino acids
1.
2.
Essential amino acids – cannot be made by the body, so
must be consumed
Non-essentials – can be made from other amino acids in the
body
Protein and exercise
1.
Not used as a fuel, therefore low priority.
2.
Only used in extreme circumstances
3.
Normal diet contains enough protein
(10 -15%).
Excess protein can lead to;

Less intake of CHO
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Increase in fat intake from animal
products
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Increase in fluid waste
VCE Physical Education - Unit 3
 Contribute
5-10% of the total energy
requirement of endurance events
 Requires large amounts of oxygen to break
down to produce energy
 A hard training athlete will need to increase
protein intake to assist in muscle growth and
repair
 CHO rich foods are also good sources of
protein e.g. Breakfast cereals, bread and
pasta
 Low
intensity (moderate walking) exercises
use approx even amounts of fats and CHO
 As exercise intensity increases CHO becomes
the primary fuel used by the muscles.
 The body even with low levels of body fat
will not run out of fat stores but has limited
stores of glycogen
 Fat can produce more ATP but the process of
converting fat is not efficient (requires more
oxygen)
 Protein only used when glycogen and fat
stores are depleted such as ultra-marathons.
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Into what does the body break down CHO’s?
In what form and where is CHO stored within the body?
Into what does the body break down Fats?
In what form and where is fat stored within the body?
Define ‘Glycogen Sparing’.
Discuss how ‘Glycogen Sparing’ benefits endurance athletes.
Explain how lowering blood glucose levels influences
athletes.
How could the athletes increase their blood glucose levels
during exercise?
Outline the type of diet an endurance athlete should
consume 3 days prior to competition.
Look at Figure 5.4 and 5.5. In your own words, explain what
the diagrams are depicting.
Major source of energy
 Chemical fuel source
 Energy is released when one of the phosphates splits
off.
 Only a small amount exists in the muscles: sufficient
for a few maximal contractions
 ATP must be continually resynthesised so that
energy can be provided for longer periods of time
 To rebuild ATP, energy from the breakdown of PC is
used
 ATP is resynthesised almost as quickly as it is broken
down.
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