Aerobic and anaerobic
pathways – an introduction
to the energy systems
3
This knowledge includes:
e • introduction to the characteristics of aerobic and anaerobic pathways (with or without
kely
edg
kno
w
oxygen) and their contribution to movement and dominant ÿbre type associated with
each pathway.
These skills include the ability to:
identify the dominant energy pathway utilised in a variety of aerobic or anaerobic
key
s
skill •
activities determined by the intensity and duration of the activity. Collect, analyse and
report on primary data related to responses to exercise and anaerobic and aerobic
pathways.
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e
t
p
a
ch preview
ATP-PC energy system
Alactacid system
Phosphocreatine system
Movement
Interplay
Energy
systems
Anaerobic glycolysis
energy system
Lactic acid system
Lactacid system
Aerobic energy system
Aerobic glycolysis system
Oxygen system
Food fuels
Muscle fibre types
Fast twitch
Slow twitch
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CHAPTER 3: Aerobic and anaerobic pathways – an introduction to the energy systems
45
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All body movements require energy for muscle contraction, whether it be walking, riding a bike,
dancing, swimming, playing a team sport or running. Where does this energy come from, how is
it produced and used by the body at rest and during exercise, and what does this energy enable
us to do? A clear understanding of energy systems will help you to understand your body better.
This chapter will provide you with a comprehensive introduction to the characteristics of energy
systems and their contribution to movement and the dominant muscle fibre type associated with
each pathway.
Foods and their conversion to energy
Food is the primary source of energy, but it cannot be used directly. Digestion is the body’s way
of breaking down food into nutrients that are then absorbed. Nutrients are carried away in the
bloodstream to the cells of the body. Some of this fuel is used immediately for energy production.
The remainder is stored in various forms and at different sites (see Table 3.1). The foods we eat
contain nutrients, which are essentially the chemical substances carbohydrates, fats, proteins,
vitamins, minerals and water.
Carbohydrates (CHO), fats and proteins are the only sources of fuel energy. To utilise these
nutrients for muscle action, the body converts the nutrients to a common ‘energy compound’
called adenosine triphosphate (ATP). The energy in food is chemical energy, which is converted
into mechanical energy to allow for muscular contractions. Movement, therefore, is a result of the
chemical breakdown of food. The chemical energy is supplied through the breakdown of ATP,
which is resynthesised almost as quickly as it is broken down by the breakdown of the stored
nutrients releasing energy.
3.1
How food is stored in the body
Food fuel
Stored as
Site
Carbohydrate
Glucose
Glycogen
Excess as adipose tissue
Blood
Muscle and liver
Around the body
Fat
Fatty acids
Triglycerides
Adipose tissue
Blood
Muscle
Around the body
Protein
Muscle
Amino acids
Around the body
Carbohydrates
glucose
a sugar
We need carbohydrates to fuel physical activity – they are the body’s preferred source of fuel,
particularly during exercise. A carbohydrate-rich diet is essential for a physically active person.
Carbohydrates play a key role in the performance of exercise lasting an hour or more. Therefore,
carbohydrate intake before, during and after exercise to meet the fuel requirements of the
activity is vital.
Carbohydrates are the sugars and starches found in fruit, cereal, bread, pasta
and vegetables. Carbohydrates serve as major food fuels for the production of ATP.
There are two forms of carbohydrates used for this purpose – blood glucose and
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muscle and liver glycogen. Muscle glycogen and blood glucose play key roles in
glycogen
intense exercise bouts, with the body’s glycogen stores playing an important part in
the form in which
carbohydrates are stored in
sustained aerobic activity such as distance running.
the muscle and liver
We don’t eat glucose and glycogen directly – carbohydrates in foods are
insulin
converted to glucose for immediate energy and to glycogen to be stored in the
a hormone that regulates the
muscle. Glucose is a specific form of sugar and is found in the blood. Glucose is
level of glucose in the blood
absorbed from the intestines into the bloodstream after you eat. The blood carries
pancreas
a gland that is both an
glucose to the muscle, where it enters the muscle through the aid of insulin.
endocrine and exocrine gland
The pancreas secretes insulin in response to the increase in blood glucose.
Insulin is an important hormone that regulates the level of glucose in the blood by
allowing glucose to be transferred from the bloodstream into the muscle. Without insulin,
your body would not be able to process glucose and would
therefore have no energy for movement or other
w?
functions.
u kno
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glycogen
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Once inside the muscle, glucose is used
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as fuel for everyday activity, such as breathing,
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walking and running. However, not all the glucose
most durin rest. In order to me es
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is used immediately; excess glucose is stored in the
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achieved t ates. The brain main
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within the muscle. The liver stores about one-third of
of ca
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the body’s total glycogen. About two-thirds is stored
y reserve
emergenc e deprivation.
within skeletal muscles, where it is very important as
cos
severe glu
a primary source of energy for muscle contractions,
especially during high-intensity exercise.
Fats
Fats are essential in our diet and perform many vital roles. For example, fats are involved in:
• protecting body organs
• maintaining body temperature
• hormone production
• energy stores for the body.
It is the role of fats as a fuel source in physical activity that is of greatest interest to students of
physical education.
Fats are not all the same – some fats are better for you than others. Essential fats (EFAs), such
as omega-3, are vital to overall health and wellbeing. Tuna and salmon are sources of omega-3.
The overconsumption of fat, however, can increase the risk of diseases.
There are many sources of fats including butter, margarine, eggs, oil and nuts. Fats, or lipids,
are found in the body in the form of triglycerides, stored in the fat cells (adipose tissue) located
throughout the body and in skeletal muscle. Triglycerides are broken down into free fatty acids,
which are broken down aerobically to provide energy for movement.
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CHAPTER 3: Aerobic and anaerobic pathways – an introduction to the energy systems
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Fats are the body’s preferred source of fuel at rest; as
you sit here reading this book, your body is using fat.
Fats are also used during prolonged submaximal
exercise. A greater amount of oxygen is required
by the body to utilise fats as a fuel than to
use carbohydrates to produce ATP. Fats
are capable of producing more ATP than
carbohydrates. However, the conversion
rate is less efficient in terms of the
amount of oxygen required to produce
the same amount of ATP. In terms
of the total amount of energy
produced, fat has a higher energy
content than carbohydrate, so is
a more powerful fuel.
y
.1 A health
f ig u r e 3
in
ta
n
co
ould
diet sh
ounts of
balanced am fats and
s,
te
carbohydra
s.
protein
Protein
Foods that are rich in protein include meat, fish, poultry, eggs and cereal. Proteins are more
complex and have larger molecules than either carbohydrates or fats. Their main role in the
body is for growth and repair of tissue. Proteins are sometimes referred to as the building blocks
of the body. All enzymes (which speed up chemical reactions) are proteins. The
enzymes
basic structural unit of proteins are amino acids. Like carbohydrates and fats,
chemical substances that
proteins have a vital role in energy production – protein is used as a fuel source in
facilitate or speed up the rate
of reactions occurring within
long-duration endurance exercise. Protein is also often associated with strengththe body
building exercise.
T H IN K IN G
T H IN G S
THROUGH
1
2
3
4
ers
>>answ
Identify which foods carbohydrates are typically found in.
Identify which foods fats are typically found in.
Which foods are proteins typically found in?
Outline why carbohydrates are the body’s preferred source of fuel.
Foods for rest and exercise
The type of food used for energy production depends on the duration and intensity of the exercise.
Similarly, the usage of food fuels is determined by whether or not a person is exercising or resting.
At rest, the aerobic energy system is the dominant system in operation, with fats contributing about
two-thirds of the food fuel and carbohydrates contributing about one-third. This is because the
body is working submaximally, with the cardiorespiratory system working to supply the cells with
enough oxygen for the production of ATP. There are no fatiguing by-products. The contribution of
proteins is minor.
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Once a person starts to exercise, both
Anaerobic
ATP  Lactic acid
the anaerobic and aerobic energy systems
Glucose 1
contribute to ATP resynthesis. The
3
duration and the intensity of the exercise
 O2 Aerobic
ATP  CO2  H2O
Fats 2
being undertaken largely determines
3
which energy system is predominant.
A marathon runner who runs for
y sources when
fi gu re 3.2 Energ
around 2 hours 30 minutes will be
t
res
at
is
dy
the bo
using the aerobic energy system, with
carbohydrates being the preferred
fuel. This is because the marathon is
predominantly a low-intensity submaximal
activity. The longer the marathoner runs,
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tigued, ea
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the more their glycogen stores will gradually
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the more dominant fuel will vary for different
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of the time and duration and the need for
immediate fuel.
Energy systems
The breakdown of ATP releases energy for muscular contraction. Stored within the muscle
is a limited quantity of ATP, responsible for movement. ATP is continually being used and
resynthesised, which enables the body to keep moving. There are three energy systems
responsible for the manufacturing of ATP and there are essentially two mechanisms for
producing ATP – the aerobic and anaerobic pathways. ‘Aerobic’ literally means with oxygen,
while ‘anaerobic’ means without oxygen.
There are two types of anaerobic system:
• The ATP-PC system – also known as the alactacid or phosphocreatine (or creatine phosphate)
system
• The anaerobic glycolysis system – also known as the lactic acid or lactacid system
There is only one aerobic system, which is also known as the aerobic glycolysis or
oxygen system.
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Energy is needed for everyday activities and exercise. The amount of energy required during
exercise by the body depends on the intensity and duration of the exercise being undertaken. If
you were to run around the local sports oval at a very high speed and intensity, you would only
be able to sustain this effort for a relatively short period of time. But if you were to run at lower
intensity, you would be able to sustain this activity for longer. We can further categorise each
running activity according to the demand for ATP, the duration of each activity, the presence
of oxygen (or not) and the intensity. Remember, though, that while there will always be one
dominant system, the three energy systems do not function independently; all three systems ‘turn
on’ at the start of exercise.
ATP-PC system
The first energy system/pathway is the ATP-PC system. It is immediately available, is the simplest
and quickest system for breaking down PC (phosphocreatine) to create ATP, and is stored in
muscle cells. This system does not require long chemical reactions, does not use oxygen and is
used for high-intensity activities involving explosive movements such as sprinting, long jumping
and throwing the javelin.
This system is dominant for the first 1–5 seconds of an activity, with peak power being
between 2 and 4 seconds, and is exhausted after about 10 seconds of intense activity. Once PC
has been depleted, 50 per cent replenishment is achieved within 30 seconds of passive recovery;
total replenishment takes 3+ minutes. The ATP-PC system is therefore linked to the fitness
components of muscular power and speed. If it were not for this system, explosive powerful
activities would not be possible.
PC is not used for muscle contraction; it is mainly used for resynthesising ATP. ATP is broken
down to adenosine diphosphate (ADP). As rapidly as this breakdown occurs, the remaining PC
is broken down to join with the ADP to form ATP again. This is the resynthesising process of ATP.
The ATP-PC system does not require oxygen, and there are no waste products produced – it does
not produce lactic acid. However, this system is very short in duration.
The process cannot continue indefinitely as the stores of PC deplete. After the initial
10 seconds when the PC stores totally deplete, the next energy system becomes dominant and
there is increased reliance on the anaerobic glycolysis system to supply ATP. Remember – the
energy systems contribute energy sequentially but in an overlapping way.
As discussed in Chapter 1, fast-twitch fibres are better suited to short-duration highintensity anaerobic work requiring performers to call upon speed, power and explosive
efforts. Once these fibres are recruited they begin to rapidly produce metabolic by-products
that cause fatigue and hence can only be used for a very short time. For example, an elite
100-metre sprint runner has a predominance of fast-twitch fibres, which have the capacity
to produce a large force when activated. But the athlete will fatigue quickly; therefore,
we say this athlete has a low fatigue resistance. Fast-twitch fibres have high stores of
phosphocreatine, but are low in oxidative enzymes and myoglobin. Recall that the ATP-PC
system does not use oxygen, so characteristics associated with the oxygen system will not be
predominant when considering fast-twitch fibres.
It becomes easier to understand individual athletes’ fibre make-up by considering the
predominant energy system being used. The elite 100-metre sprint runner, who is able to
complete the race in 10 seconds, requires speed and explosive power. This athlete will have
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high numbers of fast-twitch fibres. As the
race predominantly utilises the ATP-PC
system (determined by the duration and
the intensity), this athlete will have high
phosphocreatine stores, as this is the
quickest source of immediate energy
under anaerobic conditions. In short, the
100-metre sprint runner has the fibres that
are best suited to the event they perform.
Anaerobic glycolysis
or lactic acid system
ntly
sprint predomina
e 100-metre
es.
fi gu re 3. 3 Th
and fast-twitch fibr
system
The anaerobic glycolysis (lactic acid)
uses the ATP-PC
sports that
her examples of
ot
of
ink
th
Can you
system involves the incomplete breakdown
?
e this system
predominantly us
of carbohydrates. The energy is obtained
from the breakdown of glycogen; however, as oxygen is not present, glycogen is not completely
broken down and pyruvic acid is formed. As with the ATP-PC system, the anaerobic glycolysis
system does not require oxygen; however it does produce lactic acid (which accumulates
within the muscle), which leads to an accumulation of hydrogen ions. This in turn increases
muscle acidity, decreasing muscle pH and preventing the coupling of cross-bridges
(see Chapter 1).
The decrease in pH also impedes the action of glycolytic enzymes, which will decrease
the rate at which glycogen is broken down to form ATP. Next time you are swimming
with maximum effort, visualise this happening in your muscles. This will further help you
understand and explain that burning sensation or feeling of exhaustion you experience during
this type of activity. The lactic acid produced is also broken down to glycogen to produce
further energy.
3 .4 A
g
performin
t
gymnas
e
rs
o
lh
a pomme ominantly
d
routine pre aerobic
n
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th
s
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use
system an
glycolysis bres. Can
fi
fast-twitch e colour
th
you recall
re
t-twitch fib
of the fas
type?
f ig u r e
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This system is normally used for activities that last between 10 and 75 seconds. Anaerobic
glycolysis is more complicated than the ATP-PC system, involving many more chemical reactions.
The energy is obtained by breaking down glucose (either stored in muscles or from the bloodstream).
Peak power occurs between 5 and 15 seconds. Anaerobic glycolysis, like the ATP-PC system, is
critically important to the functioning of the human body because it provides a rapid supply of ATP,
thereby enabling the continuation of high-intensity effort. When the anaerobic glycolysis system is
used for ATP production, there comes a time when the high-intensity effort cannot be sustained. The
performer will either stop (due to fatiguing factors) or reduce the intensity of the effort. This system
is typically used in 100-metre freestyle swimming at the elite level, or a pommel horse routine in
gymnastics that lasts 30–45 seconds. The anaerobic energy system is linked to the fitness components
of muscular power and speed.
Like the ATP-PC system, the anaerobic glycolysis energy system predominantly recruits fasttwitch fibres. Performers undertaking activities predominantly using the anaerobic glycolysis system
benefit from the presence of glycolytic enzymes and the high contraction speed of fast-twitch fibres.
Glycolytic enzymes will speed up glycogen breakdown during high-intensity efforts lasting beyond
10 seconds, such as a 50-metre freestyle sprint swim.
Aerobic energy system
The aerobic energy system uses oxygen and is by far the most powerful of the three energy systems.
The preferred food fuel for the aerobic energy system during activity is carbohydrates from stores
in the muscle or from the blood. The aerobic energy system is also known as aerobic glycolysis – or
the breakdown of glucose in the presence of oxygen. The clear difference between anaerobic and
aerobic glycolysis is the complete breakdown of glycogen with no fatiguing toxic by-products. The
waste products are carbon dioxide, which we breathe out (respiration), and water. In order for this
system to function, oxygen must be present.
At rest the aerobic system uses fats. However, fats are also used as a food fuel by the aerobic
system during activity, particularly during extended endurance exercise. Fats can produce more
ATP than carbohydrates, but they require more oxygen to produce the equivalent amount of ATP.
Aerobic glycolysis occurs within the mitochondria – known as the powerhouses of the cell.
The aerobic energy system is the slowest to contribute to ATP resynthesis – due in part to the many
complex chemical reactions. If the intensity of the activity is not too high and the body has the
necessary stores of glucose and triglycerides, then the activity can continue indefinitely.
The aerobic energy system will be the dominant system for activities such as sitting and walking,
and for sustained endurance activities such as a 5 km run, that are said to be of submaximal intensity
– or less than 80 per cent of maximum heart rate (usually in the zone of 60–80 per cent). Peak power
occurs between 1 minute and 1 minute 30 seconds, and this energy system is the dominant system
for activities that are more than 75 seconds in total duration. A marathon runner will have a welldeveloped aerobic system, as would a midfielder in Australian Rules football and a midcourt player
in netball. The fitness component linked to this system is cardiorespiratory endurance.
There are three stages in aerobic energy production, responsible for the release of energy:
• Stage 1 – the breakdown of carbohydrates and fats to produce 2 ATP molecules
• Stage 2 – Kreb’s cycle, which involves the breakdown of pyruvic acid into carbon dioxide.
Further energy is released to resynthesise to ATP for a net production of 1 ATP molecule.
• Stage 3 – the electron transport stage, which involves water, heat and produces the largest yield
of ATP – a total of 34 molecules
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n runner
ho
.5 A marat
stem.
f ig u r e 3
e aerobic sy is
th
s
se
u
y
inantl
d to th
suite
predom
pes are best
What fibre ty ?
vity
type of acti
Slow-twitch muscle fibres are best suited to aerobic, endurance-based activities. Marathon
runners have predominantly this fibre type. Slow-twitch fibres contract slowly and repeatedly but
have a low force capacity.
Slow-twitch fibres are high in:
• oxidative enzymes
• mitochondria density
• fatigue resistance, as the muscle can continue to be called upon to work over an extended
period of time
• capillary density.
Recall that the aerobic energy system relies upon the blood to deliver oxygen to the
working muscle to understand why these characteristics would be high. For a more
detailed discussion of fibre types, refer to Chapter 1.
T H IN K IN G
T H IN G S
THROUGH
1
2
3
Remember that all three
energy systems are activated
at the start of exercise and
no single system works by
itself. All systems are in
play all the time, no matter
what you are doing. Just
as the aerobic system is
activated and utilised for
the 100-metre sprinter in
their 10-second maximum
effort, so too the 1500-metre
swimmer will activate all
three systems as they dive
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ers
>>answ
Summarise each energy system by listing the key characteristics of each.
Explain why we call upon the ATP-PC energy system at the start of exercise.
Outline the key difference between anaerobic and aerobic glycolysis.
ADP  Pi
ATP
Energy
Glycogen
Glucose
Pyruvic acid
(insufficient oxygen)
Lactic acid
Anaerobic glycolysis
Glycogen
Glucose
Pyruvic acid
(sufficient oxygen)
CO2  H2O  ATP
Energy
ADP  Pi
ATP
e
figur
bic
aero
3 .6 An
bic
vs aero
is
glycolys
Aerobic glycolysis
CHAPTER 3: Aerobic and anaerobic pathways – an introduction to the energy systems
53
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off the starting blocks. At any given time though, there will be a dominant system. The following
Real World Focus will help enhance your understanding of interplay of the energy systems in a
team game situation.
Energy systems
ATP-PC
Anaerobic glycolysis
Lactic acid
Aerobic glycolysis
Aerobic
Anaerobic power
LME
LME
Muscular power
Speed endurance
Aerobic power
Agility
Anaerobic power
Muscular power
Muscular strength
Speed
tionship
The rela s and
e 3 .7
ystem
figur
nergy s
ne
betwee mponents
co
s
fitnes
REAL
O
W RLD
FOCUS
Energy system interplay in an intermittent team sport activity
Kate plays centre for her local netball team.
The 2-minute warning before the start of the game booms over the
loudspeaker, as Kate stands waiting for the game to start. Her aerobic energy system is
dominant, as the intensity is low and the demands for energy production are being met
by the delivery of oxygen to the working muscles.
The whistle signifies the start of the game. Kate steps into the circle, makes a pass
and then pushes off explosively, sprinting to make position to receive the next pass. To
fuel this explosive movement, the dominant system is the ATP-PC system – PC is the fuel
source. Kate continues to move at pace, cutting and driving, continually making position
to receive the next pass. Kate has now been working for 17 seconds at high intensity,
and her anaerobic glycolysis system has become dominant, so glucose is the fuel.
Kate jumps into the air to intercept an opponent’s pass, landing and passing to
the goalshooter in the one action. Kate’s movement drops to a low-intensity walk; her
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>>
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>>
heart rate drops, allowing her to replenish some PC and remove metabolic by-products.
Breathing heavily, she walks towards the goal ring in case the opposition rebounds the
shot. The goal is missed and the ball is quickly transferred out of the opposition team’s
defensive third. Forced to defend, Kate pushes off to man up and defend her opponent,
rapidly moving from a standing start to a sprint. This rapid transfer from a stationary
position to a sprint requires immediate energy, and as her PC has been depleted (and
not been fully replenished) and her movement interspersed with low-intensity activity,
the anaerobic glycolysis system is again called upon to power this short effort.
Kate’s team wins back possession. Kate’s work rate drops to a cruise, before she
again sprints to take possession, catching and passing in one action. This change of
intensity sees Kate move between the energy systems, the anaerobic glycolysis system
fuelling the explosive activities. This time Kate’s team scores a goal.
Kate moves from a stationary position (resting) to a jog to a cruise to get back in
position to defend the centre pass. These movement patterns are repeated throughout
the game: Kate moves from periods of continual motion at high intensity to low intensity
to standing still. It will not be until quarter or half-time break (2+ minutes) when Kate can
be at complete rest, and she will have the opportunity replenish her PC stores.
Kate’s movement patterns are typical of a ‘mobile’ player. A set position player such
as a goalkeeper will have longer periods of low-intensity activity (and rest periods) with
intermittent high-intensity efforts.
Netball could be
described as an aerobic
game interspersed with
high-intensity activities.
As the type of activity
changes, so too does
the contribution of the
energy systems°– at
any given time there
will be one dominant
system. For this
reason we refer to
this as ‘interplay’.
The duration of the
activity will determine
which system is used
primarily, but they are
all used to some extent.
.8 After
f ig u r e 3
orld
the Real W
reading
ss
etball, discu
Focus on n of the three
y
the interpla
ems.
energy syst
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CHAPTER 3: Aerobic and anaerobic pathways – an introduction to the energy systems
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The following Real World Focus looks at the energy system interplay involved
in a 30-minute run.
REAL
WORLD
FOCUS
lactate inflection point (LIP)
the moment when the body
is unable to prevent the
accumulation of the hydrogen
ions associated with the
conversion of lactic acid to
lactate in the working muscles
Energy system interplay in a continuous individual activity
Each night Steve completes a 30-minute run. As Steve takes his first couple of
steps, he is using the ATP-PC system. As the intensity of the run is low initially, the
PC stores will not be depleted as rapidly as they would if he was sprinting. The ATPPC system will be the dominant system at the start as it is the immediate provider
of energy, PC being the chemical fuel. As Steve continues his run, his PC stores will
drain away, while his anaerobic glycolysis system will be increasingly contributing to
energy production through the breakdown of glycogen (as will the aerobic system).
After 25 seconds, oxygen has still not made its
way to the working muscle, so he is still working
anaerobically – the anaerobic glycolysis system would
become the main energy supplier. The intensity of
the effort is low, and although fatiguing by-products
are being produced as a result of the incomplete
breakdown of glycogen, the amount of lactic acid
being produced is not enough to slow Steve down
or°cause discomfort.
Steve is finding breathing difficult initially because
he is in oxygen deficit – a period of transition where
his body is able to provide the energy necessary for
muscle contraction without oxygen, until such time
as oxygen can be delivered to the working muscle
to enable the complete breakdown of glycogen.
During this temporary oxygen shortage, lactic acid
will not reach lactate inflection point (LIP) levels, so
he will not need to reduce the intensity at which he is
running while the aerobic energy system is increasing
its contribution, eventually allowing for a seamless
transition between the last of the anaerobic systems
and the oxygen system, around the 30-second mark.
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Peak power for the aerobic energy system will occur between 1 minute and 1 minute
30 seconds.
As oxygen is now being delivered to the working muscle through the bloodstream Steve
settles into a comfortable running pattern; his demands are being met aerobically,
his breathing is constant. It is at this point that Steve reaches a steady state. While
steady state
there is minimal replenishment of his PC stores, there is not enough to allow for
the point during exercise
this system to be called upon again. It will not be until Steve completes his run and
when oxygen supply equals
oxygen demand
his body has been at complete rest for at least 3 minutes that his PC will be totally
excess post-exercise
replenished.
oxygen consumption
Steve has now been running for around 12 minutes. A slight hill forces
an increased rate of oxygen
him to work harder. His heart rate becomes elevated in direct relation to the
following strenuous exercise
increased workload (during this short period Steve will experience another
oxygen deficit period), and although his anaerobic glycolysis system increases
its contribution, the aerobic system remains the major contributor of energy. After
90 metres, the terrain levels out again, and Steve returns to a steady state, the demands
of the run being met aerobically. He will encounter several more hills on his run, which will
see an increased contribution from the anaerobic glycolysis system, but not enough to
make it the most dominant system.
With 250 metres to go to the end of his run, Steve wants to finish strongly, so he
increases his stride length. At this point, there is almost a linear increase in oxygen
consumption to match the increase in exercise intensity. Even as Steve powers home, and
again the anaerobic glycolysis system increases its contribution to energy production, the
aerobic system will remain the dominant supplier of energy.
The run finished, Steve walks around breathing heavily. His body has already gone into
recovery phase or excess post-exercise oxygen consumption. ATP is being resynthesised,
PC is being restored, lactic acid is being oxidised and his core temperature is returning to its
normal values.
As Steve continues his cool-down walk, munching on his watermelon, the smell of
spaghetti bolognaise titillates his senses; and tomorrow he will do it all again.
T H IN K IN G
T H IN G S
THROUGH
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Explain how the energy system interplay varies between the two Real World
Focus examples.
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student activity
p r a c t ic
The 20-metre multistage shuttle-run test
a c t iv it
AIM
To gain an understanding of the contribution and
interplay of the energy systems.
EQUIPMENT
Suitable flat area with two lines 20 metres apart,
CD player and instruction CD of 20-metre
multistage shuttle-run test
METHOD
1
This test requires you to run continuously
between two lines. It can be done as a
whole-class activity. Starting from one line,
on the first beep, run to the other line.
2 Wait for the next beep before running again.
Upon hearing the beep, pivot and run in the
reverse direction, reaching the other line in
time for the next beep.
3 At each beep, you must have reached one
of the 20-metre lines.
4 As the test proceeds, the interval between
beeps reduces, so that you have to increase
speed in order to continue the test, until the
you find it impossible to reach the line in time.
5 Once you cannot reach within two strides of
the line twice in a row, finish the test. The
al
y
last number announced before
finishing is your score.
RESULTS
Complete a laboratory report utilising the data
you have collected.
DISCUSSION
1
Which muscle fibre type would you be most
reliant upon in this test? Briefly justify your
response.
2 List two characteristics of the fibre type used
when performing this test, other than colour.
3 Name three sports that you believe this test
to be specific to. Justify your response with
specific movement patterns from these
sports.
4 The 20-metre multistage shuttle run test
predominantly relies upon carbohydrates
as food fuel. Fats can provide more ATP
than carbohydrates, yet they are not our
preferred exercise fuel. Briefly discuss why.
5 With specific reference to the data obtained,
clearly discuss how all three energy systems
work together (interplay) to supply energy
throughout the test. Explain your response by
referring to duration and intensity.
tes
.1 0 Athle
f ig u r e 3
ep test
be
running the
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Chapter Summary
• Food is the body’s primary source of energy,
but cannot be used directly. Digestion is
the body’s way of breaking down food into
nutrients, which are then absorbed.
• Foods contain nutrients, which are chemical
substances. Carbohydrates, fats, proteins,
vitamins, minerals and water are essential to
our diet.
• One of the roles of nutrients is to provide
energy. Carbohydrates, fats and proteins are
used as fuel for reactions in the body – they
provide us with energy or the capacity to
do work or physical activity. To utilise these
nutrients for muscle action, the body converts
the nutrients to a common ‘energy compound’
called adenosine triphosphate (ATP).
• Carbohydrates are the sugars and starches
found in fruit, cereal, bread, pasta and
vegetables. Carbohydrates serve as major
food fuels for the production of ATP.
• Fats or lipids are found in the body in the
form of triglycerides, stored in the fat cells
(adipose tissue) located throughout the body
and in skeletal muscle. Triglycerides are
broken down into free fatty acids, which
are broken down aerobically to provide
energy for movement.
• Proteins are more complex and have larger
molecules than either carbohydrates or fats.
Their role in the body includes growth and
repair of tissue. Proteins are sometimes
referred to as the building blocks of the body.
• The breakdown of ATP releases energy
for muscular contraction. Stored within
the muscle is a limited quantity of ATP,
responsible for movement. ATP is continually
being used and resynthesised, which
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•
•
•
•
•
•
•
enables the body to keep moving.
There are three energy systems responsible
for the manufacture of ATP and there are
essentially two mechanisms for producing
ATP – the aerobic and anaerobic pathways.
The two types of anaerobic systems are
the ATP-PC system, also known as the
alactacid or phosphocreatine system, and
the anaerobic glycolysis system, also known
as the lactic acid or lactacid system.
There is only one aerobic system – the
aerobic glycolysis or oxygen system.
The ATP-PC system is immediately available,
is the least complicated and quickest system
for breaking down PC to create ATP, and is
stored in muscle cells.
The anaerobic glycolysis (lactic acid) system
involves the incomplete breakdown of
carbohydrates. The energy is obtained
from the breakdown of glycogen. However,
as oxygen is not present, glycogen is not
completely broken down and pyruvic acid is
formed.
The aerobic energy system uses oxygen
and is by far the most powerful of the three
energy systems. The preferred food fuel for
the aerobic energy system during activity is
carbohydrate from stores in the muscle or
from the blood. The aerobic energy system
is also known as aerobic glycolysis – the
breakdown of glucose in the presence of
oxygen.
All three energy systems are activated at the
start of exercise and no single system works
by itself. All systems operate all the time, but
at any given time, there will be a dominant
system.
3
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review Questions
Multiple choice
1
Which of the following nutrients are used as
fuel for reactions in the body?
A Carbohydrates, vitamins and proteins
B Carbohydrates, minerals and fats
C Proteins, fats and minerals
D Carbohydrates, fats and proteins
2 The first energy pathway is the:
A lactacid system
B aerobic glycolysis system
C alactacid system
D oxygen system.
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Short answer
4 Explain the difference between anaerobic
glycolysis and aerobic glycolysis.
5 The game of soccer predominantly relies
upon the food fuel of carbohydrates. Fats
can provide more ATP than carbohydrates,
yet they are not the preferred exercise fuel.
Briefly discuss why.
6 Explain the term ‘energy system interplay’.
3 Which of the following predominantly uses
the anaerobic glycolysis system?
A 100-metre freestyle swim at elite level
B 100-metre sprint in athletics
C Golf swing
D Marathon run
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