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CHAPTER 2
CHAPTER 2
Energy systems
The energy for muscular contractions comes from
adenosine triphosphate (ATP), which is found in
several sources including our food and drink. It may
be released from carbohydrates, fats or proteins,
depending on the body’s state of activity or health.
The body produces adenosine triphosphate
via three energy pathways. Each is the main provider under specific exercise conditions, but all
contribute to energy across all degrees of activity.
Each energy system has strengths and weaknesses
when compared with the others, and specific
sporting performances exemplify each system’s
majority contribution to the production of adenosine
triphosphate.
This chapter explores the three basic chemical
pathways in the production of adenosine triphosphate: the phosphate energy system, the anaerobic
glycolysis system and the aerobic system, along
with their relative characteristics and interplay.
The lactate threshold is a major concept in energysystem theory.
To understand the relationship between energy
systems and physical activity, it is useful to have
a knowledge of microscopic muscular activity and
how it utilises ATP; however, note that the microscopic structure of muscles is no longer assessable
under the 2006–09 VCAA Physical Education
study design.
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Assessment tasks
Task
Topics
Page
Written reports
Individual diet and energy (activity 2)
The citric acid cycle and the electron transport chain (activity 5)
61
71
Case study analysis
Elite performers’ diet and energy (activity 1)
61
74
Laboratory reports
The phosphate energy system (activity 3)
The anaerobic glycolysis system (activity 4)
The aerobic glycolysis system (activity 7)
67
69
76
Structured questions
The onset of blood lactate accumulation (activity 8)
77
After completing this chapter, students should be able to:
CHAPTER 2
Data analysis exercise Phosphate energy efforts linked to the other energy systems
(activity 6)
• Identify the characteristics of the three
and the effect that the onset of blood lactate
energy systems and the fuels required for
accumulation (OBLA) has on effort
physical activity.
• Analyse why fatigue occurs and how this is
• Describe the ways in which ATP is produced
linked to fuel depletion and metabolic
under different activity conditions and the
by-products
processes of muscular contraction
• Outline the central role that the lactate
• Explain the interplay between the three energy
threshold has in activity intensity and duration.
systems under varying activity intensities
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Why energy?
Your body needs energy for basic body functions and activity during your
whole life — energy for breathing, sleeping, digesting, sitting in a chair,
sprinting for a bus, and everything else you do day and night.
The interaction between muscles and bones keeps the body upright and
under control. To allow this teamwork between the muscular and skeletal
systems (see chapter 5, Live It Up 1 second edition), the body needs energy
sources that permit muscles to work — for example, the effort needed by the
abdominal and back muscles to enable good sitting posture, or by the muscles
of the abdominals, back, legs, torso and arms during a softball game.
Adenosine triphosphate
The chemical compound adenosine triphosphate (ATP) provides the energy
that allows muscular effort. ATP is the energy source for all muscular effort,
whether for a small subconscious movement such as the blinking of an eye,
or a planned repetitive effort in weight training (see chapters 7 and 9).
Sources of ATP
ATP is an end-product of your diet. All the food, processed drinks and water
that you consume contain nutrients that your body requires for:
• healthy growth
• repair of body ‘wear and tear’ from everyday activities
• energy for all bodily functions.
The components of a healthy diet are:
• carbohydrate
• fat
• protein
• vitamins and minerals
• water.
ATP can be created from carbohydrate, fat and protein. Chapters 3 and
11 more fully explore the processes by which the body produces energy
from food.
Carbohydrate
When carbohydrate is digested, it is broken down to glucose for blood
transportation and then stored as glycogen in the muscles and liver.
Glycogen can provide the energy for ATP production under both anaerobic
(no oxygen required) and aerobic (oxygen required) conditions.
Fat
Fat provides the major source of energy for long-term physical activity.
During a long team game or a marathon, fats (as either triglycerides or
free fatty acids) usually contribute to ATP production to meet sub-maximal
energy demands. Under special conditions, the athlete may be able to use
fat earlier in the activity to ‘spare’ the carbohydrate stores and therefore
enable longer high-level effort (see chapter 11). During rest conditions, fat
produces the majority of the required ATP.
Protein
Protein only minimally contributes to ATP production. In extreme circumstances (such as starvation or ultra triathlon/marathon events) when the
body has severely depleted its supplies of carbohydrate and fat, proteins
can become a viable source of ATP.
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Table 2.1
Assesment tasks
The body’s storage
of food fuel
Food fuel
Stored as
Site
Carbohydrate
Glucose
Glycogen
Adipose tissue
(including storage of excess
carbohydrate)
Blood
Muscle and liver
Around the body
Fat
Free fatty acids
Triglycerides
Adipose tissue
Blood
Muscle
Around the body
Protein
Muscle
Amino acids
Skeletal muscle
Body fluids
Activity 1
Key knowledge
• Fuels required for physical
activity and the conversion of
food to energy
Case study analysis
Elite performers’ diet and energy
Choose one of the research tasks below and write a brief account of
your findings. In your account, try to address these questions: How
much emphasis is given to carbohydrate, fat and protein? Why?
a Use the Internet to research the diet of one or more top Australian
athletes. (Alternatively, go to www.jaconline.com.au/liveitup/book2
and click on the Australian Sports Commission link.)
or
b Interview a local high-level sportsperson, asking them about
their diet.
Activity 2
Key knowledge
• Fuels required for physical
activity and the conversion of
food to energy
Written report
Individual diet and energy
Record your total diet for three days. Assess the percentages
of carbohydrate, fat and protein. Using your own dietary
knowledge as a guide, how could you improve your diet to
meet your energy needs? Write a brief report on your findings.
Energy from ATP
Adenosine
(three phosphate
molecules attached)
ATP
Food
Energy
ATP is stored in limited quantities within muscle, so
each muscle fibre must be able to create its own supplies from the food fuels. Figure 2.1 illustrates how the
metabolism of food creates ATP, which then provides
energy for muscular exertion.
Energy
Muscle
activity
ADP + P
Adenosine
(two phosphate
molecules attached)
Figure 2.1:
+ Free phosphate
CHAPTER 2
Energy for muscular activity —
from food to ATP to muscles
ENERGY SYSTEMS
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ATP is an adenosine molecule with three phosphate molecules attached.
When muscular activity is needed, one of the phosphate molecules
breaks off, releasing energy and creating adenosine diphosphate (ADP).
This process is reversible: figure 2.2 shows how ADP can become ATP. This
occurs continually during the activity as long as sufficient energy substrates
are available.
Food + muscle substrates
Figure 2.2:
The conversion of ADP to ATP
ADP
+
Free phosphate
+
Energy
ATP
Depending on the type of physical activity (see chapter 8, Live It Up 1
second edition), energy substrates include phosphocreatine, glucose, glycogen, lactic acid, fat, protein and oxygen.
A muscle fibre stores only a small amount of ATP, so the force and duration of a muscular effort is only as effective as the ATP replenishment
process. During and after physical exertion, the body uses several methods
of recovery to rebuild used supplies of ATP and food fuels. Chapter 4 investigates this recovery process.
Energy for rest and activity
The body can create energy (ATP) under two main conditions:
1. rest conditions, where there is sufficient oxygen available for the body to
continue to function at a resting level
2. active conditions, where physical exertion means there is insufficient oxygen available for the body to continue to function at a
particular level without a marked increase in oxygen intake either during
or after the effort. These conditions occur during anaerobic activity and
aerobic activity.
ATP production during rest conditions
Rest is when the body is not under physical stress and when breathing and
heart rates are at resting levels. The body has an abundant oxygen supply,
so it produces approximately two-thirds of the ATP from fat stores within
the muscle and elsewhere in the body. Fat is a much richer energy source
than carbohydrate. To release this energy, the body must use much more
oxygen than it would in activating the supplies of ATP from glucose.
When at rest, you have an abundant supply of oxygen which is above the
body’s metabolic demands.
The other third of ATP needed under rest conditions comes from carbohydrate in blood glucose and glycogen stores within both the muscle and
liver. As with fat, glycogen is broken down in the mitochondria (structures
within the muscle cell, referred to as the ‘powerhouses’ of the cell; see figure
2.12, page 71).
The end products of aerobic metabolism are carbon dioxide, water
and heat. No by-products limit body activity; only food fuels and the rate
of aerobic metabolism limit ongoing aerobic ATP production.
ATP production during activity
‘Activity’ in physical education is a wide-ranging term that covers any
physical state more exertive than rest. The level of activity is determined by
factors such as:
• how long the activity continues (activity duration)
• how hard the body works during the activity (activity intensity)
• the level of the individual’s aerobic fitness
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• the level of recovery achievable between activity efforts.
When the body starts physical activity, it immediately demands an
increased oxygen supply to the working muscles. The respiratory and circulatory systems (see chapter 6, Live It Up 2) are unable to meet this immediate
demand, so the body uses two energy pathways to create ATP anaerobically
(that is, without oxygen). These anaerobic pathways produce ATP quickly
and powerfully, but they have three disadvantages:
• they produce relatively small amounts of ATP
• they operate for only a short period
• they result in fatiguing by-products.
If the physical activity is at a reasonably sub-maximal level, then the body
is able to produce the required ATP aerobically because the body’s ability
to use oxygen can meet the muscles’ demands for extra oxygen for greater
ATP production. This aerobic pathway has opposite qualities to those of the
two anaerobic systems:
• it can produce ATP for sub-maximal efforts for long periods of time
• it cannot quickly produce energy for high-intensity efforts
• it has no toxic by-products.
The body produces ATP under these varying levels of physical activity
via three energy pathways: the phosphate energy system, the anaerobic glycolysis system and the aerobic system.
Note:
The following information on the
microscopic structure of skeletal
muscle, pages 63–5, is not
assessable under the 2006–09
VCAA Physical Education study
design. However, it has been
included here as it provides a
useful understanding of the end
product of each of the three energy
systems — muscular contractions.
Tendon
Belly
Microscopic structure of
skeletal muscle
As the end product of each of the three energy systems, adenosine triphosphate directly initiates all muscular contractions.
A knowledge of the microscopic structure of skeletal muscle is needed to
appreciate the role of ATP. A more thorough understanding of muscle groups
and action is found in chapter 5. Skeletal muscle is covered with a layer of
connective tissue called the epimysium. The epimysium thickens as it reaches
the ends of the muscle to form tendons that usually attach to bone.
Skeletal muscle consists of thousands of muscle fibres that run the length
of the muscle and are arranged in bundles called fasiculi. (A single bundle
is called a fasiculus.) Each individual muscle fibre is surrounded by connective tissue called the endomysium which binds the fibres together to form
the bundles. The fasiculi are surrounded by a layer of connective tissue
called the perimysium which helps bind the fasiculi together.
Muscle fibre
Endomysium: connective tissue that binds
fibres together to form bundles
Epimysium: layer of
connective tissue that
thickens to form tendons
at ends of muscle
Tendon
Perimysium: connective tissue
that surrounds the fasiculi
Figure 2.3:
Fasiculus: bundle of muscle fibres
The muscle belly in
cross-section
CHAPTER 2
ENERGY SYSTEMS
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The muscle fibre
Figure 2.4:
Scanning electron micrograph
of an insect flight muscle.
You can see three large muscle
fibres, along with the individual
myofibrils making up the fibres.
Each muscle fibre is surrounded by a cell membrane called the sarcolemma.
Underlying the sarcolemma is a gel-like fluid called sarcoplasm. This fluid
contains:
• mitochondria, which are the site of aerobic energy production
• myoglobin, which carries oxygen to the mitochondria
• fat, carbohydrate and protein (energy nutrients)
• adenosine triphosphate (an immediate energy source)
• enzymes, which are chemicals that speed up energy production
• actin and myosin myofilaments (contractile proteins).
Each muscle fibre is made up of long strands called myofibrils. Each
myofibril consists of many individual units (called sarcomeres) that are
responsible for contracting the muscle.
Sarcomeres
A sarcomere is a contractile unit, and each one is designated by a line at either end called a Z line. Each
sarcomere consists of two protein myofilaments called
actin and myosin. Actin is a thin filament that attaches
to the Z line. Myosin is a thick filament situated between
each of the actin filaments. Figure 2.5 illustrates the
several bands and zones that help define the sarcomere:
• the I band, where only actin is found
• the A band, where both actin and myosin are found.
It equates with the length of the myosin filaments.
• The H zone, where only myosin is found. It is the gap
between the ends of the actin.
I band
A band
Myofibril
Z line
Z line
Muscle fibre
Sarcomere
Myofibril
Z line
H zone
Z line
Cross bridge
Figure 2.5:
Arrangement of sarcomeres
within the muscle fibre
Thick (myosin) filament
Thin (actin) filament
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Cross bridges
The myosin filaments have cross bridges (oar-like structures) that are
attracted to the actin filaments (figure 2.5). At rest, there is little contact
between the actin and the myosin; however, when the sarcomere contracts,
the cross bridges attach to the actin filaments and pull them into the centre
of the sarcomere in a ‘rowing’ action.
The cross bridges continue to detach and reattach themselves from the
actin filaments, shortening the sarcomere. Every sarcomere along the muscle
fibre shortens, leading the whole muscle to contract. The muscle will relax
when the actin and myosin filaments lose contact with each other — that is,
when the cross bridges detach from the actin.
A band
Figure 2.6:
Structural rearrangement of actin
and myosin filaments at rest
(at 1) and during contraction (2–4)
H zone
I band
Z line
1
2
3
4
Source:
S. Powers and E. Howley,
2004, Theory and Application to
Fitness and Performance, 5th edn,
© McGraw-Hill Companies, Inc.
CHAPTER 2
ENERGY SYSTEMS
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Three energy systems
All three energy pathways operate at any one time, but the contribution
of each varies depending on the intensity of the activity. Figure 2.7 illustrates the overlapping nature of the three energy systems which underpins
their ‘interplay’. Note that the identified percentage contribution of each
energy system to exertions of different durations has changed with sports
physiology research over the years.
A graphic interpretation of the
three energy systems and their
periods of importance
100
Figure 2.7:
75
Aerobic energy
50
25
0
Anaerobic glycolysis
Phosphate energy
0 10 30 60 90 120
180
240
300
360
Phosphate energy system
The phosphate energy system has some alternative names (usually shorthand versions): the phosphocreatine (PC) system, the ATP–PC system, the
phosphagen system or the PC (or CP) system.
This system provides the bulk of ATP during powerful or explosive
efforts. Such efforts may be a one-off, such as a court-length pass in basketball or a take-off in the high jump, or ongoing, such as a sprint to position
in netball or football. The phosphate energy system is closely linked with
several fitness components (see chapter 5):
• muscular strength
• muscular power
• anaerobic power
• speed
• agility
• reaction time.
Following about 10 seconds of maximal effort, the phosphate system is
largely depleted and the body needs to significantly reduce the activity’s
intensity as the anaerobic glycolysis system begins to become the dominant
provider of ATP. The phosphate energy system relies on muscle stores of
both ATP and a chemical compound called ‘phosphocreatine’.
If the activity requires a maximal effort for 5–10 seconds, such as a
100-metre sprint event, then stores of ATP and phosphocreatine in the
working muscles jointly create most of the maximal effort for that activity.
From the push off the starting blocks until a few seconds into the sprint,
the muscles’ ATP stores provide the energy for the repeated muscular contractions. ATP supplies in the muscles diminish, and the amount of ADP left
from the spent ATP grows. At this point in the race, the stores of phosphocreatine create new ATP from the ADP, allowing the performer to complete
the sprint. The chemical bond holding the phosphate and the creatine
together is quickly broken, releasing energy that is used to reconstitute ATP
from ADP (figure 2.8).
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Figure 2.8:
Creatine
The release of energy from
phosphocreatine for ATP
production is quick and efficient,
but short-lived.
ATP
Phosphate
Energy
Energy
Creatine
ADP + Free phosphate
From just a few seconds into an all-out phosphate effort, the anaerobic
glycolysis system begins to work (Journal of Science and Medicine in Sport,
vol. 6, Issue 2, June 2003). This results in increasing levels of lactate and
hydrogen ions within the working muscles. However, these levels do not
inhibit muscular action at this stage.
After about 10 seconds of effort, the muscles’ stores of phosphocreatine
are also greatly depleted. Thus, with critically low stores of both ATP and
phosphocreatine, the athlete must either slow down or stop.
Once this maximal effort is over, the body is able to take in more oxygen
via puffing. This extra oxygen is able to create more ATP from ADP,
and to reconstitute phosphocreatine from the broken phosphate and
creatine molecules remaining after the sprint.
Following a 10-second maximal effort, the body can take around
3–5 minutes to fully restore the ATP and phosphocreatine supplies to preexercise levels within the working muscles. Latest research suggests
50 per cent phosphocreatine replenishment can happen in the 30 seconds of
rest recovery (Journal of Science and Medicine in Sport vol. 6, Issue 2, June 2003).
If the effort was less than 10 seconds, then the recovery time to pre-exercise
levels is relatively faster at 5 minutes. Chapter 4 contains more detail on this
recovery process.
Key knowledge
• Characteristics and interplay
of energy systems for physical
activity and recovery in
relation to duration, intensity
and type of activity
Key skills
• Describe the interplay of
the energy systems,
using correct terminology.
• Analyse the relationship
between energy systems and
physical activity.
• Perform, observe, analyse
and report on laboratory
exercises designed to explore
the relationship between
energy systems during
physical activities.
• Identify and explain the
relationship between physical
activity, muscular fatigue
and recovery.
Activity 3
Laboratory report
The phosphate energy system
As a class, choose three test subjects to thoroughly warm up
and then attempt a series of 50-metre sprints. Allow gradually
reduced recovery periods after each sprint of:
• 5 minutes
• 3 minutes
• 1 minute
• 10 seconds.
Each subject takes their heart rate for 10 seconds after each sprint.
If you are not a test subject, help organise and record the runs.
a Graph and discuss the results.
b Write a report in which you explain the peak time for the
phosphate energy system,
its required recovery
period and how
the laboratory
demonstrated
this theory.
CHAPTER 2
ENERGY SYSTEMS
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Anaerobic glycolysis system
Figure 2.9:
Jana Pittman winning another
400-metre hurdles race. Her effort
produces a large amount of lactate
and hydrogen ions.
The anaerobic glycolysis system also has some alternative names:
the lactic acid system or the lactacid system. This system mainly
provides the bulk of ATP production during high-intensity, submaximal efforts. It may also become the dominant producer of
ATP during repeated phosphate efforts which have insufficient
recovery time to allow full phosphocreatine replenishment. Further,
when a performer has gone beyond their maximum oxygen uptake
level (their VO² max — see page 75) during an endurance event,
the anaerobic glycolysis and aerobic systems share the task of
creating ATP for the few minutes it will take the performer to stop
from exhaustion. In this situation approaching exhaustion, a performer is working at greater than 100 per cent of their maximum
oxygen capacity. This is due to the anaerobic input into the effort.
Chapters 5 and 7 will further investigate this situation.
The anaerobic glycolysis system operates as the dominant supplier of ATP in the period from around 10 seconds of maximal
effort to around 60 seconds of high-intensity sub-maximal effort.
Most recent studies suggest that the overlap period — when the
body switches from using the anaerobic glycolysis system as the
dominant ATP producer to using the aerobic system — could start
as early as 30 seconds into high-level, sub-maximal activity.
The anaerobic glycolysis system is closely linked with several fitness
components (see chapter 5):
• anaerobic power
• local muscular endurance
• speed
• muscular power.
It is classically exemplified in the 400-metre run in secondary school athletics,
but it is also highly relevant in a team game when the performer is required
to undertake repeated sprints that do not provide sufficient recovery time
for the phosphate system. Most players in team games can relate to a situation of having insufficient energy to allow continued top effort, and thus
needing a time-out or a rest on the substitution bench. Chapter 4 more fully
explains the steps leading to this fatigue.
During the 400-metre athletic event, the production of ATP relies on all
three energy systems but predominantly on anaerobic glycolysis. When the
athlete pushes off the starting blocks, the phosphate energy system allows
for an explosive start to the race. However, this system quickly loses its
primary role in ATP production as anaerobic glycolysis begins to dominate.
The glycogen stores within the muscle are worked on (without the need
for oxygen in the muscles) to create ATP, allowing the muscles to continue to
propel the body down the back straight of the 400-metre track. The working
muscles need ATP at a faster rate than can be adequately provided by the
complete breakdown of glucose through aerobic metabolism. Therefore,
the pyruvic acid created by anaerobic glycolysis cannot be processed by
oxygen, and it is converted to lactic acid. Hydrogen ions are also released
(figure 2.10 opposite).
When lactate and hydrogen ions accumulate in the muscles during
high-intensity exercise, muscular contractions are inhibited. The body can
tolerate increasing levels of lactate and hydrogen ions production only until
their accumulation rate is greater than the body’s ability to remove them.
At this stage there is an exponential increase in lactate and hydrogen ions
levels within the muscle. This is called the lactate threshold: once the athlete
passes this threshold, they must reduce or stop their muscular effort.
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Key knowledge
• Characteristics and interplay
of energy systems for physical
activity and recovery in
relation to duration, intensity
and type of activity
Key skills
• Describe the interplay of
the energy systems,
using correct terminology.
• Analyse the relationship
between energy systems and
physical activity.
• Perform, observe, analyse
and report on laboratory
exercises designed to explore
the relationship between
energy systems during
physical activities.
• Identify and explain the
relationship between physical
activity, muscular fatigue
and recovery.
Activity 4
Laboratory report
The anaerobic glycolysis system
As a class, thoroughly warm up and then run a 400-metre race.
a Stop when you reach the point when you think your lactate
levels are beginning to affect your running.
b In groups of four to six students, write up your responses
and present them to the class.
The energy used by a busy rover during an Australian Football game or
a wing attack during a netball game also relies on anaerobic glycolysis for
a large proportion of ATP production during the game. The recovery time
for the phosphate energy system after an exhaustive 10-second maximal
effort is about 3–5 minutes. Therefore, after a 5-second maximal effort, the
recovery time is roughly equivalent to 1–2 minutes; after a 1-second effort, it
may be about 10 seconds.
Glycogen
Glucose
ATP
Energy
for
muscle
Energy
ADP + Free phosphate
Figure 2.10
The process of anaerobic
glycolysis is more complex than
the phosphate energy system,
with around eleven steps
compared with two.
Pyruvic acid
no oxygen
Lactic acid
+
hydrogen ions
CHAPTER 2
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During 20 minutes of a football or netball game, an involved player
may carry out over 100 phosphate efforts (see chapter 5). Even if adequate
oxygen-rich recovery conditions are available between each effort, there is
still only around 10 seconds for recovery each time. Therefore, the phosphate energy system usually becomes severely depleted in sources of ATP
production, and the next quickly available system (anaerobic glycolysis)
takes over as the dominant ATP supplier.
During a 400-metre run, lactic acid accumulating in the leg muscles
affects the runner in the home straight but generally can be endured until
the end of the race. In a team game, however, too much lactic acid build-up
will impair subsequent performance and cannot be ignored.
Aerobic energy system
The aerobic energy system includes the aerobic glycolysis system. It is relevant to all of the fitness components because it provides either the basis
for recovery between strength and power efforts, or the bulk of energy for
sub-maximal efforts.
Aerobic glycolysis, as with all the energy systems, contributes to ATP
production under all conditions. However, it contributes the majority of
ATP during continuous sub-maximal activities which go beyond 1 minute.
This system can create thirty-eight molecules of ATP from one molecule
of glucose, whereas anaerobic glycolysis creates only two. This extra amount
is possible because the abundance of oxygen allows a more complete breakdown of glucose than occurs in anaerobic glycolysis. Pyruvic acid, rather
than becoming lactic acid, is further broken down in the citric acid cycle
and the electron transport chain within the mitochondria (figure 2.12).
Figure 2.11:
Glycogen
The process of aerobic
glycolysis is more complex than
the other two systems,
providing both advantages and
disadvantages in ATP production.
Glucose
ATP
Energy
for
muscle
Energy
ADP + Free phosphate
Pyruvic acid
(+ oxygen)
Fats (and oxygen)
+
Protein (emergency
ATP source)
Citric acid
cycle
ATP for muscle
Hydrogen
ions
Electron
transport chain
ATP for muscle
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Key knowledge
• Characteristics and interplay
of energy systems for physical
activity and recovery in
relation to duration, intensity
and type of activity
• Fuels required for physical
activity and the conversion of
food to energy
Key skills
• Analyse the relationship
between energy systems and
physical activity.
• Identify and explain the
relationship between
physical activity,
muscular fatigue
and recovery.
Activity 5
Written report
The citric acid cycle and the electron transport chain
Find some reliable physiology websites on the Internet. The
following search words should be of help:
• aerobic energy
• ATP
• citric acid cycle
• electron transport chain
• fat oxidation
• muscle energy.
Write a report on either:
a fat oxidation within the citric acid cycle
or
b hydrogen ions, their role in fatigue and their oxidation in the
citric acid cycle and electron transport chain.
With the rich oxygen supplies in the aerobic system, fat is able to become
a significant contributor to ATP production. One molecule of fat can release
over 100 molecules of ATP, but at a much slower rate than the release
from glucose. Fat requires a complex series of reactions that depend on
oxygen within the citric acid cycle in the mitochondria. (Protein is similarly
metabolised for ATP production, but only under the extreme conditions
mentioned earlier.)
The body’s supply of fat exceeds even the physical requirements of a
highly trained athlete, so the aerobic system can theoretically operate for an
unlimited work period. What prevents us happily jogging, cycling or swimming forever are a few other factors concerning our bodies during physical
activity:
• dehydration
• hypothermia or hyperthermia
• muscle damadge
• joint damage
• specific energy-system enzyme inactivation
• neural fatigue
• mental fatigue or boredom
• time pressures — other things to do!
Mitochondrion
Figure 2.12:
The mitochondrion carries out
aerobic glycolysis, involving
glycogen breakdown that
produces water and carbon
dioxide as by-products.
Also, pyruvic acid is now further
broken down in the citric acid
cycle, and both fat and protein
can be metabolised.
Glycogen
Glucose
Fat
ATP
Pyruvic
acid
Protein
Citric
acid
cycle
Carbon
dioxide
Hydrogen
Oxygen
ATP
Electron
transport chain
CHAPTER 2
Water
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Characteristics of the aerobic system
• Much slower energy production than that of the anaerobic systems
• Lag of 2–5 minutes until the individual reaches a ‘steady state’ (where the
respiratory system’s increased oxygen intake meets the activity’s oxygen
demands). The aerobic production of ATP plateaus at the required exercise intensity level (figure 2.13).
• Dominant contributor to ATP production only at sub-maximal exercise
conditions
• Limited contribution to ATP production once the lactate threshold is passed,
given the increasing debilitating effects of lactate and hydrogen ions.
Figure 2.13:
When you begin to exercise, the
more quickly responding
anaerobic systems contribute the
bulk of ATP production until the
aerobic system reaches its steady
state 2–5 minutes later.
Total ATP production
ATP production
Anaerobic
production
Aerobic systemʼs
production
Onset of exercise
0
3
5
Time (minutes)
Table 2.2
Summary of the three energy systems
Characteristic
Phosphate energy
Anaerobic glycolysis
Aerobic glycolysis
1. Energy source for ATP
production
Phosphocreatine
Carbohydrate
Glycogen
Carbohydrate
Fat
Protein
2. Number of ATP
molecules made
from one molecule of
energy source
Phosphocreatine:
less than one
Glucose:
approximately two
Glucose: thirty-eight
Fat: more than 100
3. Maximal rate of
ATP production
(molecules/minute)
3.6
1.6
1.0
4. Duration of peak
energy production
5–10 seconds
30–45 seconds
3–7 minutes (time
above the lactate
threshold; see
pages 75–6)
5. Percentage
contribution at 25 per
cent of VO² max
Less than
5 per cent
Approximately
15 per cent
Approximately
80 per cent
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Table 2.2 (continued)
Summary of the three energy systems
Characteristic
Phosphate energy
Anaerobic glycolysis
Aerobic glycolysis
6. Percentage
contribution at 65 per
cent of VO² max
Approximately
5 per cent
Approximately
45 per cent
Approximately
45 per cent
7. Percentage
contribution at
maximal sprint
55 per cent
40 per cent
5 per cent
8. Recovery time until
repeat effort
Phosphocreatine
replenishment:
3-5 minutes
• 50 per cent recovery
in first 30 seconds
• Rest recovery best
Depends on time above
lactate threshold.
Removal of lactic acid to
rest levels:
• with active recovery:
– 50 per cent removal:
15 minutes
– 95 per cent removal:
30 minutes
• with passive recovery:
– 50 per cent removal:
30 minutes
– 95 per cent removal:
60 minutes
Restoration of body
glycogen stores:
• after competition of
more than 1 hour:
24–48 hours
• after hard interval
training: 6–24 hours
9. Limiting factor when
operating maximally
Depletion of
phosphocreatine
Lactate and hydrogen-ion
accumulation
Lactate and hydrogenion accumulation
• Glucose and
glycogen stores
• Overheating
(hypothermia)
10. Intensity and duration
of activity where the
system is dominant
ATP provider
Maximal intensity
(>95 per cent) and
duration of
1–10 seconds
High, sub-maximal
intensity (85–95 per cent)
and duration of 10–30
seconds
Sub-maximal intensity
(85 per cent) and
duration of >30 seconds
11. Specific sporting
examples
• Any athletic field
event
• Elite 100 m athletic
sprint
• Golf drive
• Gymnastic vault
• Volleyball spike
• High mark and long
kick in AFL
• Tennis serve
• Water polo centre
forward–centre back
contest
• 200–400 m in athletics
• 50 m swim
• Consecutive basketball
fast breaks
• High intensity 15–20
second squash rally
• Repeated leads by AFL
full forward
• Elite netball centre in
close game
• Quadriceps in
downhill skiing
• Water polo consecutive
fast breaks and defends
•
•
•
•
•
•
•
•
Marathon
Cross-country skiing
Triathlon
AFL mid field
Hockey wing
All elite team players
Rowing 2000 m race
Water polo game
12. Everyday activity
examples
• Running up one
flight of steps
• Carrying heavy
shopping from
car to house
• Sprinting for train
• Running up four flights
of stairs
• Running 200 m to catch
bus
• Chopping wood
• Moving heavy furniture
•
•
•
•
•
•
Shopping
Going to the cinema
Gardening
Dancing
Ironing
Studying
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Key knowledge
• Characteristics and interplay
of energy systems for physical
activity and recovery in
relation to duration, intensity
and type of activity
• Fuels required for physical
activity and the conversion of
food to energy
• Muscular fatigue mechanisms,
specifically fuel depletion,
metabolic by-products,
and dehydration
Activity 6
Data analysis exercise
Phosphate energy efforts linked to the other
energy systems
Watch a replay of any high-level team game (either a professional
recording or one you have filmed yourself). Assign groups to
record all phosphate efforts by the players.
a Assess the average length of each effort and the average recovery
time between each.
b Determine the relative importance of each of the three energy
systems to the game.
Key skills
• Describe the interplay of
the energy systems,
using correct terminology.
• Analyse the relationship
between energy systems and
physical activity.
• Identify and explain the
relationship between
physical activity,
muscular fatigue
and recovery.
ATP production — different exertion
conditions
The length and intensity of physical exertion determine which of the energy
systems is the dominant contributor to ATP production (figure 2.14). As the
activity time increases, the influence of the aerobic system on ATP production
also increases. However, the relative contribution of each of the three energy
systems varies according to the intensity and duration of the activity.
Figure 2.14:
The average energy
contributions of different energy
systems during high-intensity
competition
ATP
Phosphocreatine
50%
Anaerobic
glycolytic
Aerobic
glycolytic
8%
6.3%
50%
50%
65%
44.1%
Aerobic
lipolytic
92%
30%
50%
49.6%
Source:
John Hawley & Louise Burke
1998, Peak Performance: Allen &
Unwin, St Leonards, p. 47
50%
35%
20%
6 seconds
30 seconds
60 seconds 120 seconds
1 hour
4 hours
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Energy expenditure
(cal/kg/min)
300
200
100
0
25
65
85
Exercise intensity
Fats
(% of maximum
Glycogen oxygen uptake)
Figure 2.15
The contributions of
body fat and carbohydrate
stores to activity performed at
varying percentages of
maximum oxygen uptake
ATP production
Source:
Adapted from The Physician
and Sportsmedicine,
vol. 26, no. 9, 1998
Anaerobic systems
Aerobic system
Exercise intensity
Figure 2.16:
The aerobic and anaerobic contributions to ATP production as
exercise intensity increases — the
lactate threshold is the point
at which the intensity increases
such that lactic acid production
exceeds lactic acid removal.
The contribution of either carbohydrate or fat to ATP production varies
according to the activity intensity. This is usually measured against the
maximum oxygen uptake (VO² max = the maximum volume of oxygen
that the body can use, measured in millilitres per minute per kilogram
— see chapters 6 and 8). A low-intensity activity such as walking uses
about 25 per cent of maximum oxygen uptake and elicits high levels of fat
mobilisation from around the body to generate ATP. This is one reason for
prescribing long walking sessions as a valuable exercise for weight control.
Walking mobilises only small amounts of carbohydrates, with blood glucose
supplies meeting the body’s carbohydrate needs.
Figure 2.15 indicates that an activity performed at 65 per cent of
maximum oxygen uptake (such as easy jogging) produces significant rates of
fat oxidation to create ATP; at an activity level of 85 per cent of maximum
oxygen uptake (a level at or above the lactate threshold for non-elite
athletes), fat contributions decline and carbohydrate assumes dominance
in ATP production.
OBLA
OBLA is the acronym for the onset of blood lactate accumulation. At rest,
everyone has lactic acid in their muscles. This would be measured at very
small levels of around 1mmol/L of blood.
It is only when exercise begins that the muscular levels of lactic acid (LA)
begin to rise. At the same time as these begin to rise, the levels of hydrogen
ions (H+) within the muscles also rise. If the exercise or activity is anaerobic
in nature, then the levels of both lactate and H+ rise more significantly.
At the early stages of anaerobic work, the building muscular concentrations of both lactate and H+ easily flow from the working muscles
through the capillary walls into the circulatory system. This flow follows the
widely understood maxim that ‘higher concentrations always flow towards
lower concentrations.’ In the early stages of anaerobic work, the blood and
plasma concentrations of lactate and H+ are lower than within the working
muscles.
An increase in blood and plasma levels of lactate and H+ is the signal that
OBLA has occurred. This is easily measured at elite training venues such as
the AIS in Canberra where technological facilities and sports scientists are
available to quickly take and measure blood samples from the elite athletes
that train with the AIS.
When these readings are combined with an athlete’s record of their physiological responses to exertion, training can be tightly geared around both
their OBLA and their lactate threshold.
Lactate threshold
Traditionally called the ‘anaerobic threshold’ (a misleading term), the lactate
threshold is the common term used at the elite level of sports physiology.
It is the point above which lactic acid begins to rapidly accumulate in the
blood, and below which blood levels of lactic acid do not inhibit aerobic
effort at the desired level.
Beyond the lactate threshold, muscle and blood lactate levels exponentially increase and the athlete has to reduce or stop muscle effort. For
ordinary people, the lactate threshold is usually around 4 mmol/L of LA.
Trained athletes can increase their tolerance to LA accumulation and are
able to continue effective performance or training with much higher lactate
and H+ levels in their working muscles and circulatory system.
At the AIS, athletes’ LA levels have been measured at above 20 mmol/L
while continuing to effectively train or compete anaerobically.
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Once the athlete passes the lactate threshold and continues the activity
until reaching exhaustion, all energy systems are still functioning but the
body’s increasing reliance on the anaerobic glycolysis system results in LA
and H+ levels that curtail the activity.
Figure 2.16 on the preceeding page indicates there is no exact physical
state at which the lactate threshold occurs. It will differ with each individual,
the individual’s state of fitness and the intensity of the activity. However,
some indicators (which vary in their precision) provide coaches and athletes
with a means of assessing the effort required by a work-out (table 2.3).
Table 2.3
Ways of determining the lactate threshold
Method
Determinant
1. Percentage of maximum
heart rate
Untrained athlete — around 60 per cent
Trained athlete — around 90 per cent
2. Percentage of maximum
oxygen uptake
Untrained athlete — around 50 per cent
Trained athlete — around 80 per cent
3. Blood lactate levels
Untrained athlete — 4 mmol/L
Trained athlete — more than 4 mmol/L
4. Conversation during exercise
Ability to talk continues, but extended conversation is uncomfortable.
5. Respiration
Breathing rate is still comfortable at the onset of blood lactate
accumulation but becomes more rapid as effort continues past it.
Key knowledge
• Characteristics and interplay
of energy systems for physical
activity and recovery in
relation to duration, intensity
and type of activity
• Muscular fatigue mechanisms,
specifically fuel depletion,
metabolic by-products,
and dehydration
Key skills
• Describe the interplay of
the energy systems,
using correct terminology.
• Analyse the relationship
between energy systems and
physical activity.
• Perform, observe, analyse
and report on laboratory
exercises designed to explore
the relationship between
energy systems during
physical activities.
• Identify and explain the
relationship between
physical activity,
muscular fatigue
and recovery.
Activity 7
Laboratory report
The aerobic glycolysis system
Select two high-level endurance athletes from the class and
obtain a medical clearance for each.
a Carry out an aerobic power laboratory test, such as the
Multi-Stage Fitness Test, or the Phosphate Recovery Test
(see chapter 6).
b Ensure you can record accurate heart rates.
c Predict when the onset of blood lactate accumulation is likely to
occur for each of the two subjects.
d Have the subjects perform the test to exhaustion, recording as
many body responses as possible during the test.
e Try to pinpoint when the onset of blood lactate accumulation
occurs. Give reasons for your decision.
f Try to pinpoint when the lactate threshold occurs for each. How
long after this was each individual able to continue working?
g Assess the value of the test and answer questions your teacher
will prepare. Some possible areas to investigate include:
• levels of oxygen consumption during the test
• the percentage contributions of each energy system
• differences in the onset of blood lactate accumulation for
each subject
• reasons for respiration rates and other body responses to
the test.
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Most sports participants specifically target their lactate threshold in
training in order to improve their aerobic delivery of energy (by reducing
or delaying their reliance on anaerobic metabolism). As a result, trained
athletes can generally tolerate higher levels of lactic acid in their working
muscles (see chapters 7 and 9 for more detail).
Lactic acid removal
Existing exertion levels determine the rate of lactic acid removal. An active
recovery provides the best conditions, with exertion levels less than the
level of the lactate threshold and with a heart rate ideally 15–30 beats per
minute lower than that at the lactate threshold. With blood flow greater
than at rest levels, the blood flow through the muscle capillaries is still
substantial enough to disperse lactic acid.
The bulk of lactic acid is converted back to pyruvic acid then oxidised
inside the mitochondria via the citric acid cycle, ultimately creating
new ATP supplies. During exercise and depending on the aerobic levels
of activity, lactic acid can serve as a ‘metabolic precursor’ (or energy
source). If there is ‘spare’ oxygen due to the aerobic exercise levels being
below the lactate threshold, the body can clear lactic acid through neighbouring muscle fibres in less active muscle groups, as well as through
the heart, liver and spleen. Once exercise is finished, the liver can also
reconvert lactic acid to glycogen.
Lactic acid levels during changes
in exercise intensity
Increases in exertion levels may occur at different times in sport, such as:
• with tactical surges during 1500 to 10 000-metre athletic races
• while pushing hard up a hill during a triathlon cycle leg
• when running ‘on the ball’ in Australian Football
• while closely following a talented wing attack for half of a netball game.
With sudden increases in intensity, the quickest responding energy system
is anaerobic glycolysis. When this increase in exertion is passing the lactate
threshold the quick accumulation of lactate and H+ will require a following
rest period to allow levels to fall below the threshold. Depending on how
long each excursion is beyond the lactate threshold, this pattern has to continue throughout the activity for the athlete to achieve optimal performance.
The aim is to avoid too much lactate and H+ accumulation which demands
longer periods of rest before the effort can be repeated.
Key knowledge
• Muscular fatigue mechanisms,
specifically fuel depletion,
metabolic by-products,
and dehydration
Key skills
• Analyse the relationship
between energy systems and
physical activity.
• Identify and explain the
relationship between physical
activity, muscular fatigue
and recovery.
Activity 8
Structured questions
The onset of blood lactate accumulation
1 What sporting examples (other than those detailed above)
exemplify times when athletes reach the lactate threshold?
2 How is each example a debilitating influence on the performer’s
ability to complete the event?
3 Can athletes train to delay the lactate threshold?
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Lactate as an energy source
Figure 2.17:
Blood lactate levels with
varying levels of intensity from
the beginning of exercise.
Note the existence of blood lactic
acid before exercise begins.
Recent research has focused less on the inhibiting effects of lactic acid and
more on the ability of the body to metabolise lactic acid as a source of ATP
production for muscular effort.
When the demand for ATP reduces, lactic acid can be broken down by the
body to create replenished ATP supplies. This situation of sufficient oxygen
availability is most readily found during team games or long-distance
endurance events that may be punctuated by spurts of anaerobic effort.
For example, triathlons, marathons, long-distance athletic track events, or
cycling tours.
These sporting situations will see high level anaerobic efforts followed by
a recovery phase of aerobic effort. As long as this ‘recovery’ level is below
the individual’s lactate threshold, then the excess oxygen will be able to
metabolise the extra lactic acid accumulated from the burst of higher effort.
Accompanying this change of emphasis has been greater acknowledgement of the inhibiting effects of increased muscle acidity during anaerobic
work. The rising levels of hydrogen ions (H+) within the anaerobically
working muscle are now recognised as the more significant inhibitor to
effective muscle contraction. Increased acidity upsets the normally smooth
interaction between the actin and myosin within the muscle cell’s sarcomere. It also interferes with energy generating chemical pathways of each of
the energy systems.
Onset of
exercise
Line A: start of exercise, which is maintained
at levels lower than lactate threshold
Line B: exercise intensity at levels above that
of the lactate threshold
Line C: exercise intensity at levels at the
lactate threshold
Line D: exercise intensity at levels oscillating
above and below the OBLA, given the
competition demands and available
aerobic recovery periods
B
C
D
A
Figure 2.18
Cadel Evans in the 2005 Tour
de France — controlling his
lactate threshold is of the utmost
importance.
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The article in figure 2.19 reassesses the role of lactic acid as a cause of
muscle fatigue. Read the article and discuss its ideas as a class.
Evidence mounts that lactic acid helps,
not hinders, athletic performance
By Justin Kemp and Damian Farrow
Sally Robbins stopped rowing because
of it. Paula Radcliffe ended her
Olympic marathon due to it. And the
Australian 4 x 400 metres relay team
claims that a silver medal helped cure
its ill-effects. One chemical appears to
be solely responsible for all the fatigue
and discomfort felt when exercising
to the limit — lactic acid. But is this
really true?
There are many types of fatigue
and the causes vary depending on the
duration and intensity of the activity.
Acute alterations to nerve and muscle
function, to the metabolic environment
in cells, to the availability of fuel for
energy supply and to hormonal levels
may all act to slow us down.
The brain, too, plays its part in
perceiving these signals and acting
to protect the body from damaging
over-exertion. But because lactic acid
production increases with ever-heavier
exercise, it has become the common
scapegoat to explain declines in performance at the muscle level.
When lactic acid is generated in
human cells, it immediately separates
into two components: (1) the lactate ion,
and (2) a hydrogen ion (which reflects
an increased acidosis). These two are
often touted to inhibit the force and
speed of muscle contraction, disrupt
the ionic balance of the cells and slow
the work-rate of the muscle’s energysupplying pathways.
Many studies have explored the
impact that both lactate and acidosis
has on muscle performance and this
work is now trumpeting the virtues of
lactic acid.
When lactic acid is produced during
exercise and transported from working
muscles into the bloodstream as lactate,
the heart, neighbouring and distant
muscle fibres and even the brain can
use it as an energy source. Furthermore,
the liver and kidney can convert lactate
back to glucose, demonstrating that
lactate is not the negative by-product of
metabolism that it is so often labelled.
It is actually a mobile fuel appreciated
by other tissues.
In truth, lactate is an indispensable intermediary molecule involved
in many physiological processes,
including a role in maintaining muscle
force. Professor Graham Lamb’s team
at La Trobe University has shown that
high concentrations of lactate have little
inhibitory effect on activation and contraction within single muscle fibres.
Meanwhile, scientists at Aarhus University in Denmark demonstrated that
lactic acidosis may even protect against
potential losses in the ability to activate
muscles (called muscle excitability)
and enforce output that can take place
because of inevitable potassium escape
from exercising muscle fibres.
A subsequent collaboration between
these Danish and Australian research
teams also has provided evidence that
acidosis might block the movement of
chloride across muscle fibre membranes
— a mechanism that would enhance the
excitability of the fibres.
Moving from single muscle fibre
experiments to regular exercise the
Medical School of Hanover in Germany
recently reported that an induced
acidosis did not negatively affect the
contraction speed of muscles involved
in hand-grip exercise.
Moreover, a Swedish group has
shown that some of the experiments that
implicated acidosis in muscle fatigue
do not hold when these same trials are
performed at body temperature. Some
scientists even suggest that lactate production decreases muscle acidosis.
The accumulation of lactate in the
muscle and blood during exercise
might still be a good marker to indicate
the onset of fatigue, but this in no way
declares that lactic acid causes muscle
fatigue.
There is now overwhelming evidence from myriad experimental
protocols expounding lactate as being
not harmful, and even beneficial, to
exercise performance, compared with
limited evidence to the contrary.
Source:
The Age, 4 September, 2004
Figure 2.19:
Lactic acid reassessed
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CHAPTER REVISION
Key knowledge
• Characteristics and interplay
of energy systems
for physical activity
and recovery in relation to
duration, intensity and type
of activity
• Fuels required for physical
activity and the conversion
of food to energy
• Muscular fatigue mechanisms,
specifically fuel depletion,
metabolic by-products,
and dehydration
Key skills
• Describe the interplay of
the energy systems,
using correct terminology.
• Analyse the relationship
between energy systems
and physical activity.
• Perform, observe,
analyse and report on
laboratory exercises designed
to explore the relationship
between energy
systems during
physical activities.
• Identify and explain
the relationship between
physical activity, muscular
fatigue and recovery.
Chapter summary
• The energy for physical activity is released by the catabolism (breaking
down) of adenosine triphosphate (ATP). This energy source is stored in
only small amounts within muscles.
• ATP is produced via three energy pathways:
— the phosphate energy system, which uses phosphocreatine to create
new ATP supplies without using oxygen
— the anaerobic glycolysis energy system, which uses glycogen but no
oxygen
— the aerobic energy system, which uses oxygen and primarily glycogen
and fat (and protein under extreme conditions) to create ATP.
• The phosphate energy system can create ATP very quickly, with a
major energy contribution to powerful exertions of up to around
10 seconds’ duration. It depletes quickly, taking around 3–5 minutes to
fully replenish.
• The anaerobic glycolysis system takes longer to create ATP. It is the major
contributor to high-level exertions of 10–30 seconds, but creates lactate
and hydrogen ions as by-products. The lactate threshold is the stage
when lactic acid concentrations within the blood reach the level at which
continued high-level muscle activity cannot continue. It can take up to
60 minutes to restore lactic acid to resting levels.
• The aerobic glycolysis system becomes the major contributor to muscle
activity from around 30 seconds into a sustained sporting performance.
It relies on an efficient circulo-respiratory system. The creation of ATP
within the muscle occurs in the mitochondria.
Review questions
1. Define in your own words the key terms listed below, all of which
appear in this chapter: When you have finished, check your
definitions with those in the glossary on page 435.
adenosine triphosphate
aerobic energy
anaerobic glycolysis
carbohydrate
citric acid cycle
electron transport chain
energy substrates
fat
fat oxidation
free fatty acids
glucose
glycogen
hydrogen ions
lactate
lactate threshold
lactic acid
mitochondria
mmol/L of LA
muscle acidity
OBLA
phosphate energy system
phosphocreatine
protein
steady state
triglycerides
2. Construct pie charts showing percentage energy contributions of each of
the three energy systems for the following activities:
(a) walking
(d) 1500-metre athletic race
(b) a slow jog
(e) 10 000-metre athletic race
(c) 400-metre athletic race (f) the Hawaii triathlon.
Give reasons for your energy breakdowns.
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Note:
Questions 3 and 4 review material
is not directly assessable under the
2006–9 VCAA Physical Education
study design.
3. (a) To which myofilament are the cross bridges attached?
(b) How do the cross bridges facilitate muscle contraction?
4. (a) On the following diagram of a sarcomere at rest, where do these
features appear?
Z line
A band
I band
H zone
Sarcomere
CHAPTER 2
CHAPTER REVISION
(b) What happens to each of these features during muscle contraction?
5. (a) Calcium is released during muscle contraction. From where is
it released?
(b) How does the release of calcium assist muscle contraction?
6. Name activities or sports best suited to each of the bars within the
graphs in figure 2.14 (page 74).
7. Study the bar graph in figure 2.15 (page 75).
(a) Why is exercise at 25 per cent of VO² max more useful for weight
control than exercise at higher intensity levels? Give the
physiological reasons.
(b) Why does the carbohydrate proportion increase so markedly at
85 per cent of VO² max?
8. Study the graph in figure 2.16 (page 75).
(a) Draw the graph and add the probable lactate threshold for an elite
AFL player (in mmol/L of blood) to the vertical axis. (Use table 2.3
on page 76 as a guide.)
(b) Why does the contribution of anaerobic glycolysis to ATP
production increase after the athlete reaches the lactate threshold?
(c) Define the ‘lactate threshold’. How is the term ‘onset of blood
lactate accumulation’ different?
9. Study the graph in figure 2.17 (page 78).
(a) What different sporting activity is representative of each situation
in lines A–D?
(b) Why do you think that not all the lines begin at the junction of the
X and Y axes?
(c) Why does line A have a hump?
10. Examine the data in figure 2.20 on the following page, showing times
for the four individual 100-metre splits of the three medallists in
the women’s 400-metre event at the Sydney Olympics. Answer the
following questions:
(a) State the physiological factors that explain Cathy Freeman’s much
faster third and fourth 100s when compared with Graham and Merry.
(b) Which energy system is most important to the runners over the
first 50 metres?
(c) Give reasons for your answer to question (b) above.
(d) From the data in table 2.4, use evidence to show at what point you
believe lactate levels have become an influencing factor in the run.
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CHAPTER REVISION
Figure 2.20:
Heart rate at various
exercise intensities
Source:
Reproduced from the Herald Sun,
26 September, 2000
Table 2.4
Data from
the race
100m
No. 1
No. 2
No. 3
No. 4
Total
Freeman
12.30
11.78
12.06
12.97
49.11s
Graham
12.14
11.56
12.30
13.58
49.58s
Merry
12.32
11.48
12.28
13.64
49.72s
(e) Define OBLA. Is it the reason for athletes to stop their performance
efforts?
(f) Understanding that there is a ‘usual’ circulatory system lactic acid
level where the lactate threshold is said to occur in most people, what
could Freeman’s lactic acid levels have been at the end of the race?
Give your answer in mmol/L.
(g) What is the ‘usual’ level of LA for the lactate threshold to occur?
Give your answer in mmol/L.
(h) Discuss the probable differences in the 400-metre race between
Freeman’s reaction to the OBLA and an unfit individual’s reaction.
(i) Draw three pie charts. In the first, give your estimates of percentage
contributions from each of the three energy systems for the first
200 metres of the race. In the second pie chart, give the estimated
percentage contributions for the second 200 metres of the race. In the
third, give the percentage contributions from each of the three energy
systems for the total race.
(j) Provide reasons for the divisions in each of the pie charts in (i) above.
11. (a) Describe the intensity and duration of a sporting activity where
phosphocreatine is the predominant fuel source.
(b) Name a specific sporting activity/situation that clearly illustrates the
use of phosphocreatine as the predominant fuel source.
(c) List one advantage and one disadvantage in using phosphocreatine
as a fuel.
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12. (a) Describe the intensity and duration of a sporting
activity where anaerobic glycolysis is the
predominant fuel source.
(b) Name a specific sporting activity/situation that
clearly illustrates the use of anaerobic glycolysis as
the predominant fuel source.
(c) List one advantage and one disadvantage in using
anaerobic glycolysis as a fuel.
Figure 2.21:
AFL player Luke Ball displays the
importance of all fitness
components and energy systems
to his team game.
Websites
www.anatomy.usyd.edu.au/mru/lectures/lecture2.pdf
Anatomy 2001 Muscle/
Mobility Structure
www.sport-fitness-advisor.com/anaerobicthreshold.html
Anaerobic Threshold . . .
The Key to Developing Elite Endurance
www.e-muscles.net
CHAPTER REVISION
13. Use your knowledge of team games and the way in
which players need to perform phosphate efforts
repeatedly over 1–2 hours total playing time. Reflect on
the photo of AFL star Luke Ball in figure 2.21, using it as
a prompt to add to your own experiences. Then answer
the following question: How does Ball rely on all three
energy systems to both maximise his skill and power,
and to run out the entire four quarters of the game?
e-Muscles.net
http://sln.fi.edu/biosci/systems/systems.html
‘You Have to Have a System’, The
Heart: An Online Exploration
www.lactate.com/eslact1c.html
Lactate Physiology and Sports Training
http://.home.hia.no/~stephens/lacthres.htm
The Lactate Threshold
NISMAT Exercise Physiology Corner:
A Primer on Muscle Physiology Anaerobic Threshold . . . The Key to
Developing Elite Endurance
www.nismat.org/physcor/muscle.html
web.indstate.edu/thcme/mwking/muscle.html
‘Muscle Biochemistry’, The Medical
Biochemistry Page
www.predator.pnb.uconn.edu~wwwpnb/virtualtemp/muscle/exercise-folder/muscle.html
Muscle Metabolic Systems in Exercise
http://muscle.ucsd.edu/musintro/struct.shtml
‘Skeletal Muscle Structure’ Muscle
Physiology Homepage
www.anatomy.usyd.edu.au/mru/lectures/lecture1.pdf
www.brianmac.demon.co.uk/siteindx.htm
Skeletal muscle structure
Sports Coach Page Index A–Z
CHAPTER 2
ENERGY SYSTEMS
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