1. Food fuels and the three energy systems
Text Reference
1. Nelson Physical
Education VCE Units
3&4 – Chapter 5
.

2. Key Knowledge
 Characteristics and interplay of the three energy systems (ATP – CP, anaerobic
glycolysis, aerobic system) for physical activity, including rate of ATP production,
the capacity of each energy system and the contribution of each energy system.
 Fuels (both chemical and food) required for resynthesis of ATP during physical
activity and the utilisation of food for energy.
 Relative contribution of the energy systems and fuels used to produce ATP in
relation to the exercise intensity, duration and type
Key Skills
 Describe, using correct terminology, the interplay and relative contribution of the
energy systems in different sporting
 Perform, observe, analyse and report on laboratory exercises designed to explore
the relationship between the energy systems during physical activity
 Explain the role the energy systems play in enabling activities to occur as well as
their contribution to active and passive recovery

4. Food fuels and the three energy systems

5. 1. Carbohydrates (CHO) –
Preferred source of fuel
during exercise (Glycogen)
2. Fat – Concentrated fuel
used during rest and Energy
prolonged sub-maximal
exercise.
3. Protein – Used for growth
and repair (Negligible use
during exercise)

6. VCE Physical Education - Unit 3

7. VCE Physical Education - Unit 3

8.  Complete questions 1-4 page 117 of Nelson
Physical Education VCE Units 3 & 4.

9. Food fuels and the three energy systems

11. VCE Physical Education - Unit 3

12. Food fuels and the three energy systems

13. Everything we eat is broken down
and either used immediately,
excreted or stored as chemical
energy

14. Rest (Aerobic)
 Fat and glucose are the preferred fuels
During Exercise
1. Short duration / high intensity – Anaerobic systems used using carbohydrates.
2. Long duration / low intensity – Aerobic system using carbohydrates. However, fats
are used once glycogen stores are depleted.

16. Food fuels and the three energy systems

17. Low intensity
 ATP requirements are met aerobically using the aerobic system.
High Intensity
 Explosive movements require instant supply of ATP which can’t be met
aerobically, therefore the ATP-PC and lactic acid systems need to be used
anaerobically.
Aerobic Anaerobic
Intensity increases

18. Storage (Based on 80kg person) Carbohydrate rich diet;
 Muscle glycogen – 400g  Increases glycogen stores
 Liver glycogen – 100g  Glycogen is used in rebuilding
Intake of Carbohydrates depends on ATP
the intensity and duration of CHO preferred fuel over fats during
exercise bouts. exercise due to requiring less
 Normal contribution to diet is 55- oxygen to release energy.
60% CHO Athletes need to be aware of their
 Carbohydrate loading (80% CHO dietary intakes of CHO. Excess
intake) is used for endurance CHO is converted to fat.
activities.

19. Storage of fats At rest
 Adipose tissue
 50% of energy supplied by fats
 Triglycerides
 Oxygen demand is easily met to
(Broken down into free fatty acids)
Aerobic metabolism of fat is; burn fats
 Slow as it requires more oxygen Benefits of fat
than CHOs.  Large energy store
 Adds stress to the oxygen  Transport medium for fat soluble
transport system vitamins
 ATP yield is much higher from fat Negative aspects of fat
(460 molecules) in comparison to  Adverse health effects
glucose (36).  Obesity, heart disease etc.

20. Role of protein (Amino acids) in the body;
 Growth and repair
 Speed up reactions in the body (Enzymes)
 Produces hormones and antibodies
Protein and exercise
1. Not used as a fuel, therefore low priority.
2. Only used in extreme circumstances
3. Normal diet contains enough protein (15%).
Excess protein can lead to;
 Less intake of CHO
 Increase in fat intake from animal products
 Increase in fluid waste

21. During prolonged endurance events
such as marathon running and
triathlons;
 Body uses a combination of CHO and
fats.
 Trained athletes are able to ‘spare’
glycogen and use free fatty acids.
 Fats cannot be used alone as a fuel
(poor solubility in the blood).
 ‘Hitting the wall’ occurs when
glycogen stores are depleted. This is
called ‘hypoglycaemia’.
VCE Physical Education - Unit 3

22. Glycemic index; Before exercise you should
 Rating of CHO effect on eat;
blood glucose  Food that maintains blood
 Quick breakdown with glucose levels ie.low GI food
immediate effect on blood  Avoid high GI food prior to
glucose levels are labelled exercise.
high GI  High GI cause an insulin
 Slow breakdown are surge, effecting the
labelled low GI performance of an athlete
VCE Physical Education - Unit 3

23. Food fuels and the three energy systems

24.  Aerobic exercise includes lower intensity activities performed for
longer periods of time.
 Activities like walking, jogging, swimming, and cycling require a
great deal of oxygen to make the energy needed for prolonged
exercise.
 The energy system that is used in aerobic exercise is called the
aerobic system. It can also be called ‘oxygen system’ or the
‘aerobic glycolysis system’.

25.  The term "anaerobic" means "without air" or "without oxygen."
 Anaerobic exercise uses muscles at high intensity and a high rate of work for
a short period of time.
 Anaerobic exercise helps us increase our muscle strength and stay ready for
quick bursts of speed. Examples of anaerobic exercise include heavy weight
lifting, sprinting, or any rapid burst of hard exercise.
 These anaerobic exercises cannot last long because oxygen is not used for
energy and fatiging metabolic by-products
 There are two energy systems which use the anaerobic pathways; ATP-PC
and the Lactic Acid systems

26.  The three energy systems do
not turn on and off like a
traffic light.
 They are always in operation
– the relative contribution of
each system varies
depending on factors such as
intensity, type of activity and
duration.

28. Food fuels and the three energy systems

29. How does the system work?
 Anaerobic  PC releases a free
 Most rapidly available phosphate
PC = P + C
source of ATP ADP + P = ATP
 Depends on simple
short chemical reactions  Body has a larger storage of
PC compared to ATP
 Stored PC last for 10  PC stores can be
seconds at max replenished through aerobic
recovery.
intensity  Once PC stores are
depleted, they body must
use glycogen through the
anaerobic pathway.

30. VCE Physical Education - Unit 3

31. Food fuels and the three energy systems

32. The lactic acid system; How the system works;
 Activated at the start of intense  Glycogen is broken down in the
exercise absence of oxygen (Anaerobic
 More complex reactions than the
glycolysis)
 This produces a fatigue causing
ATP-PC system by product called lactic acid.
 Peak power until it fatigues (2-3  Lactic acid makes the muscle pH
minutes) decrease (More acidic), reducing
 Predominant energy supplier in ATP resynthesis.
events 85% max HR eg. 200m The lactic acid system;
sprint.  Provides twice as much energy
for ATP resynthesis than the ATP-
PC system.
 Fatiguing metabolic by-products
produced at the lactate inflection
point (LIP)

33. The exercise intensity
beyond which lactate
production exceeds removal.

34. VCE Physical Education - Unit 3

35. Food fuels and the three energy systems

36. The aerobic system How the system works;
 Slowest contributor to ATP
1. CHOs and Tryglycerides (FFA +
resynthesis
glycerol) broken down to release
 However, produces much more
energy than the anaerobic systems energy. This produces pyruvic acid.
 Becomes major contributor once the 2. Pyruvic acid is further broken down
lactic system decreases. producing carbon dioxide (Kreb’s
 Major contributor in prolonged cycle)
exercise eg. Endurance events. 3. Further breakdown via the electron
 Aerobic system does contribute in transport chain. It requires hydrogen
maximal intensity exercise (Eg. ions and oxygen, producing water
Between 55-65% in 800m) and heat.
table 4.4 p.101 and 4.5 p.102

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39. Foods, Fuels and Energy Systems

40. VCE Physical Education - Unit 3

42. Foods, Fuels and Energy Systems

43. All activities use some energy from all three systems.
The energy systems overlap – they never work independently.
It it’s the relative contribution of each system that varies.

46.  Complete questions 1-6 page 138-139 of
Nelson Physical Education VCE Units 3 & 4.