ENERGY
DEFINITIONS
ENERGY
The ability to perform work; usually measured in Joules (J)
WORK
Work (Nm or J) = Force (N) X Distance (m)
FORCE
A push or pull that alters, or tends to alter, the state of motion of a
body. Measured in Newtons (N)
POWER
The rate at which work can be done; or Work ÷ Time. Measured in
Watts (W)
EXAMPLE:
If a 100m sprinter weighing 75kg moves 10 meters in 4 seconds,
power will be calculated as follows:
Power = force (N) X distance (m)
Time (seconds)
= 750N
4s
= 187.5 W
KINETIC ENERGY
Energy seen as muscle movement. E.g. running
CHEMICAL ENERGY
Energy stored in compounds in our bodies. E.g. ATP,
Phosphocreatine, Carbs & Fats
POTENTIAL ENERGY
Stored energy waiting to happen. E.g. ATP does nothing
until the phosphate group is released with the help of
ATPase
ATP
Adenosine Triphosphate – the only usable source of energy
for work. ATP stored in the muscles provides kinetic energy
for muscular contraction. Breaking down the high energy
bond between the last two phosphate molecules acts as
potential energy. The breakdown of ATP will only last 2-3
seconds.
High Energy Bonds
A
P
ADP
P
P
Adenosine Diphosphate
A
P
P
1
ATP/PC or PHOSPHOCREATINE (PC) or ALACTIC SYSTEM
ATPase
1)
ATP
ADP
Muscle Contraction
+
P
+
P
+
C
+
P
+
Energy
Energy
Creatine kinase
2)
PC
Energy
3)
ADP
+
1)
=
ATP is broken down into ADP and P and releasing Energy for Muscle
Contraction. This is an Exothermic Reaction, which releases energy.
When ATP levels fall and ADP levels increase, this stimulates the release
of Creatine kinase which breaks down PC.
2)
=
PC is broken down into P and C (by Creatine kinase) and releasing Energy
to Re-synthesis ATP
3)
=
ADP and P receive Energy from the breakdown of PC to join P onto
ADP to make ATP. This is an Endothermic Reaction, which requires
energy to be added.
ATP
NOTE:
2) and 3) are termed a COUPLED REACTION due to the product of one
reaction (Energy) is used in another reaction.
NOTE:
The ATP/PC System is the predominant energy system during high
intensity, short duration movements or events, e.g. 100m sprint, long/triple
jump, explosive jumping or diving etc.
TRAINING ADAPTATIONS
Anaerobic Training overloads the ATP/PC system and increases the body’s muscle stores
of ATP and PC. This delays the threshold between the ATP/PC and the Lactic Acid
System andtherefore increases the potential duration of high intensity exercise for up to 12 seconds.
2
ADVANTAGES AND DISADVANTAGES OF THE ATP/PC SYSTEM
ADVANTAGES
No O2 required
DISADVANTAGES
Only a small amount of ATP and PC
stored in muscle cells
Only one ATP is re-synthesised for one
PC
Only provide energy to re-synthesise
ATP for a maximum of 10 seconds
PC stored in muscle cell as readily
available energy source
Very quick re-synthesis of ATP
Provides energy for high intensity
exercise
No harmful by-products that will cause
fatigue
Recovery for this system is very quick
due to quick re-synthesis of PC
NOTE:
The ATP/PC System works under Anaerobic conditions.
The fuel for this system is Phosphocreatine.
This reaction takes place in the sarcoplasm of the muscle cells.
LACTIC ACID SYSTEM
This is also know as Anaerobic Glycolysis (the partial incomplete breakdown of Glucose
into Pyruvic Acid)
GLYCOGEN (stored in the Muscles/Liver)
GPH
GLUCOSE (C6H12O6)
PFK
2ATP re-synthesised
LDH
LACTIC
ACID
(C3H6O3)
PYRUVIC ACID (C3H4O3)
KEY
GPH
=
Glycogen Phosphorylase. Converts Glycogen to Glucose
PFK
=
Phosphofructokinase. Enzyme that helps break Glucose down
into Pyruvic Acid
LDH
=
Lactate Dehydrogenase. Converts Pyruvic Acid into Lactic Acid
NOTE:
There is NO Oxygen present!!!
3
NOTE:
The main limitation of this system is the Onset of Blood Lactate
Accumulation (OBLA) – which lowers the pH and inhibits enzymes.
NOTE:
The Lactic Acid system is the predominant energy system for the 400m
sprint and for midfield games players that have lots of high intensity sprints
with no time for recovery
TRAINING ADAPTATIONS
Repeated bouts of anaerobic training which overload the LA system also increase the
body’s tolerance to lactic acid. This will increase the body’s stores of Glycogen. This also
delays the effect of OBLA and prolongs the Lactic Acid threshold.
ADVANTAGES AND DISADVANTAGES OF THE LACTIC ACID SYSTEM
ADVANTAGES
Relatively large amount of Glycogen
stored in muscles/liver and is readily
available
Re-synthesises two molecules of ATP –
more than ATP/PC System
Requires few chemical reactions than
Aerobic System, so provides a quicker
supply of energy
GPH and PFK enzyme activation due to
a decrease in PC
Can work aerobically and anaerobically
Provides energy for high intensity
exercise lasting between 10 and 180
seconds
NOTE:
DISADVANTAGES
Not as quick as the ATP/PC System
Produces Lactic Acid, which is a fatiguing
by-product
Reduces pH of muscle cell (making it
more acidic) which inhibits the enzyme
action
Stimulates pain receptors
Net effect is muscle fatigue and pain
The Lactic Acid System works under Anaerobic conditions.
The fuel for this system is Carbohydrates (in the form of Glycogen).
The reactions take place in the sarcoplasm of the muscle cells.
4
AEROBIC SYSTEM
GLYCOGEN
1)
GPH
GLUCOSE
PFK
2ATP
PYRUVIC ACID
COENZYME A
+
ACETYLE CoA
OXALOACETIC ACID
+
CITRIC ACID
Sarcoplasm
2)
OXALOACETIC ACID
KREBS
CYCLE
CO2
H
2 ATP
Mitochondria
(matrix)
3)
+
H
NAD AND FAD
NADH and FADH
Mitochondria
(cristae)
O2
H+
e‾
ELECTRON
TRANSPORT
CHAIN
H2O
5
34 ATP
1)
=
Aerobic Glycolysis. Same reactions as Lactic Acid System, apart from
Pyruvic Acid combines with coenzyme A to form Acetyl CoA.
2)
=
Krebs Cycle. The Acetyl CoA combines with oxaloacetic acid to form Citric
Acid. Citric acid is then taken into the Krebs Cycle where:
 CO2 is produces and removed via the lungs
 Hydrogen atoms are removed (oxidation)
 Energy is produced to re-synthesis 2 molecules of ATP
 Oxaloacetic acid is regenerated
3)
=
Electron Transport Chain. The Hydrogen atoms (from Krebs Cycle)
combine with the coenzymes NAD and FAD to form NADH and FADH.
These are then carried down the Electron Transport Chain where hydrogen
is split into H+ and e‾. This takes place in the cristae of the mitochondria
where three important events take place:
 The hydrogen electron (e‾) splits from the hydrogen atom and
passes down the ETC
 This provides sufficient energy to re-synthesise 34 ATP molecules
 The hydrogen ion (H+) combines with oxygen to form water (H2O)
The equation for the Aerobic System would be:
C6H12O6 + 6O2
=
6CO2
+
6H2O
+
Energy to re-synthesise 38 ATP
FATS
Triglycerides (fats) are broken down by enzymes termed lipases into free fatty acids
(FFA) and glycerol and used as an energy fuel within the aerobic system. FFA are broken
down into Acetyl CoA, which enters and is broken down by the Krebs Cycle and the ETC
in the process termed beta-oxidation.
FFA produce more Acetyl CoA and consequently produce far greater energy than the
breakdown of glycogen/glucose. However, FFA’s require 15% more O2 than that required
to break down glucose. Therefore, glycogen and glucose are the preferred energy fuel
during moderate or high intensity activity.
TRAINING EFFECTS
Aerobic training causes a number of beneficial adaptations which help to improve the
aerobic energy system’s efficiency to re-synthesise ATP:
 Increased storage of muscle and liver glycogen
 Increased metabolism of aerobic enzymes
 Earlier use of FFA’s as a fuel thereby helping to conserve glycogen stores
The net effect of the above adaptations is that they increase/prolong the aerobic threshold
thereby increasing the potential intensity of performance. This delays muscle fatigue by
increasing the intensity at which the onset of blood lactate accumulation is reached and by
maximising its efficiency to remove lactate during periods of recovery.
6
ADVANTAGES AND DISADVANTAGES OF THE AEROBIC SYSTEM
ADVANTAGES
Large potential glycogen and Free Fatty
Acids (FFA) stores available as an
efficient energy fuel
Efficient ATP re-synthesis when good O2
supply guarantees breakdown of FFA
Large ATP re-synthesis. 38 ATP from
one molecule of glucose, compared to 2
from LA system and 1 from ATP/PC
system
Provides energy for low/moderate
intensity, high duration exercise (3
minutes to 1 hour)
No fatiguing by-products. CO2 and H2O
are easily removed
NOTE:
DISADVANTAGES
Slower rate of ATP re-synthesis
compared with LA system
Requires more O2 supply (15% more for
FFA)
More complex series of reactions
Cannot re-synthesise ATP at the start of
exercise due to initial delay of O2 from
the cardiovascular system
Limited energy for ATP during high
intensity, short duration work
The Aerobic System works under Aerobic conditions.
The fuel for this system is Glycogen or Fat as well as requiring Oxygen to
function.
The reactions take place in the sarcoplasm of the muscle cells, Matrix of
the Mitochondria and Cristae of the Mitochondria.
CONTROLLING ENZYMES
Energy System
ATP/PC System
Lactic Acid system
Aerobic System
Controlling Enzymes
Creatine kinase
Phosphofructokinase
Phosphofructokinase
Activator
Increase in ADP
Decrease in PC
Increase in
adrenalin/decrease in insulin
levels
DEFINITIONS
ANAEROBIC
A reaction that can occur without the presence of oxygen
ANAEROBIC
GLYCOLYSIS
The process of breaking down glucose into Pyruvic Acid
ATP
The only immediately usable source of energy in our bodies
ATPase
The enzyme that helps break down ATP to release energy
COUPLED
REACTION
The products of one reaction are then used in another reaction (see
ATP/PC System)
CRISTAE
Internal membrane/compartments/fold-like structures within the
mitochondria
ELECTRONS
A negatively charged particle of an atom (e‾)
7
ELECTRON
The process of combining H+, e‾ and O2 to produce water and
TRANSFER CHAIN provide energy for the re-synthesis of 34 ATP
ENDOTHERMIC
A chemical reaction that requires energy to be added for it to
progress
EXOTHERMIC
A chemical reaction that releases energy as it progresses
KREB’S CYCLE
The cyclical process of breaking down pyruvic acid in CO2, H+
and e‾ whilst providing the energy for the re-synthesis of 2 ATP
MATRIX
Intracellular fluid within the mitochondria where oxidation takes
place
MITOCHONDRIA
The ‘Powerhouse’ of the cell where all aerobic processes take
place
PYRUVIC ACID
Product of the partial breakdown glucose during anaerobic
glycolysis
SARCOPLASM
The gel-like content of the muscle that contains all the organelles of
the cell. It also stores glycogen, fat, proteins, enzymes and
myoglobin
THRESHOLD
The point when one energy system stops being the
predominant energy provider for the re-synthesis of ATP
8
ENERGY CONTINUUM
This is ‘the relative contribution of each energy system to ATP re-synthesis
determined by the intensity and duration of exercise.’
In any sporting situation, energy is provided by all three energy systems, and the
contribution of each is determined by the intensity and the duration of the exercise. Some
activities/sports are mainly aerobic while others are anaerobic. Energy systems rarely
work in isolation.
100
Capacity of
Energy
System (%)
Aerobic System
Lactic Acid System
ATP/PC System
0
10
20
2min
5min+
Time
Graph showing Energy System Interaction Linked to Exercise Duration
Identify the predominant energy system used in the following types of exercise:
Activity
100m Sprinter
Shot Putter
Marathon Runner
800m Runner
Tennis Player
Netball Centre
Football
Goalkeeper
Badminton
200m Swimmer
% ATP/PC
% Lactic Acid
9
% Aerobic
FACTORS AFFECTING THE ENERGY SYSTEM USED
A combination of exercise intensity and duration can determine the predominant
energy system(s) being used. When exercise intensity is anaerobic (high intensity,
short duration), then the ATP/PC and LA Systems will be predominant. If the
exercise intensity is aerobic (medium/low intensity, long duration), then the Aerobic
System will be predominant.
When the aerobic system cannot supply energy quick enough, it has to use the LA
system to continue to provide energy for re-synthesis of ATP. During high
intensities lactate production will start to accumulate above resting levels. This is
termed Lactate Threshold. When blood lactate levels reach 4mmol/L (normal
resting levels are 1-2mmol/L), the exercise intensity is referred to as ‘the Onset of
Blood Lactate Accumulation’ (OBLA). OBLA continues to increase if exercise
intensity is maintained or increased and will cause muscle fatigue.
After training the intensity level for lactate threshold is increased and this will delay
the point at which OBLA is reached and therefore increases the potential
duration/threshold of the LA energy System.
You will need to be able to explain the main factors that affect the energy system
utilise:
 Exercise Intensity and Duration (above)
 Energy System Threshold
 O2 Transport/Supply
 Food/Fuel available
 Enzyme Activation Levels
 Fitness Level
THRESHOLDS
The Threshold for any system is ‘the point at which that energy system is unable to
provide energy.’ Or ‘the point at which one energy system is taken over by another
as the predominant energy system to provide energy for ATP re-synthesis.’
Energy System Thresholds
Performance Duration
Less than 10 seconds
10-90 seconds
90 secs – 3 mins
3+ mins
Energy System(s)
Involved (predominant in
bold)
ATP/PC
ATP/PC
LA
LA
Aerobic
Aerobic
10
Practical Example
Triple Jump/100m sprint
200-400m sprint
100m swim
Boxing (3 min rounds)
800/1500m
Low impact aerobics class
Marathon
The energy system threshold alters in response to a combination of both intensity and
duration of exercise and will not always go through each energy system in turn. For
example, a cyclist cycling at a low intensity will be using the Aerobic System, although
when going up hill they may exceed the intensity threshold of the aerobic system and the
lactic acid system will take over as the predominant energy system. In team games,
players will switch between the three energy systems.
OXYGEN AVALABILITY
If there is O2 present then the aerobic system can provide energy to re-synthesise ATP. If
O2 supplies falls below that demanded by the exercise then the aerobic system threshold
is met and the lactic acid system will start to break down glucose anaerobically.
ENZYME ACTIVATION
Factors Affecting Enzyme Activation for the Energy Systems
Activating Factor
Increase in ADP; decrease
in ATP
Decrease in PC
Increase in adrenalin;
decrease in insulin
Releases Controlling
Enzyme(s)
Creatine Kinase
Activating Energy System
PFK
PFK
LA System
Aerobic System
PC
FITNESS LEVEL
The more aerobically fit the performer, the more efficient their cardiovascular and
respiratory systems are. Aerobic athletes have also shown that they can start to use FFA’s
earlier during sub-maximal exercise, which conserves glycogen stores. The overall effect
is that the aerobic threshold in terms of intensity and duration can be increased as the
lactate threshold/OBLA would be delayed.
A typical untrained athlete would reach OBLA at about 50-56% of their VO2 max, whereas
an aerobic-trained athlete would not reach OBLA until about 85-90% of their VO2 max.
An anaerobic-trained athlete will increase their ATP/PC, glycogen stores, anaerobic
enzymes and tolerance to lactic acid. All of this would increase the threshold of both
ATP/PC and Lactic Acid Systems.
FUEL AVAILABILITY
If the body has sufficient stores of PC, it is able to use the ATP/PC system for very high
intensity, short duration activity/movements. PC stores are limited, but are available at the
start and after recovery during exercise. If exercise starts too high then PC stores will
quickly deplete and exercise at that intensity cannot be sustained. PC stores can be
conserved by pacing and re-synthesising PC stores during recovery periods using spare
energy from the aerobic system.
11
Glycogen is the major fuel for the first 20 minutes of exercise. This is due to O2 supplies
being limited as it takes 2-3 minutes for the cardiovascular system to supply sufficient O2.
As well as glycogen being readily available in the muscles, requires less O2 and is easier
to break down than FFA’s. About
After about 20-45 minutes there is a greater breakdown of fats alongside glycogen as the
energy fuel. FFA’s are a more efficient fuel than glycogen, but require 15% more O2. If a
performer has larger muscle/liver glycogen store, then they can perform work aerobically
at a higher intensity.
Glycogen stores become nearly depleted after about two hours, then FFA’s have to be
used for aerobic energy production, and unless exercise intensity is reduced it can bring
on the sudden onset of fatigue (‘hitting the wall’). Once OBLA is reached the body has
insufficient O2 available to burn FFA’s and will then have to break down glycogen
‘anaerobically’ to re-synthesise ATP.
12
EXAM QUESTIONS
JANUARY 2002
1
During physical activity such as a physical education or games lesson, an athlete
will use a combination of energy systems.
The graph in Fig. 1 shows the relative contribution of aerobic and anaerobic energy
metabolism during maximal physical effort of various durations.
100
X
Y
80
Aerobic Metabolism
Duration of Maximal Exercise
Secs
Minutes
10 30 60
2
4 10 30 60 120
% of Total
Energy
Yield
%
Anaerobic
%
Aerobic
60
90 80
70
50
35
15
5
2
1
10 20
30
50
65
85 95 98 99
40
20
Anaerobic Metabolism
0
0
10
20
30
40
Maximal Work Time (mins)
50
Fig. 1
a)
At X
At Y
2
c)
With reference to Fig. 1, provide the missing information A, B and C from
the table that summarises the predominant energy system being used at
points X and Y on the graph.
(3 marks)
Predominant
Energy System
ATP-PC
Aerobic
Fuel Used
Active Enzyme
PC
Glycogen and
Fats
Creatine Kinase
A
Site(s) of
Reaction
B
C
Explain how ATP is created aerobically when you are performing a
continuous exercise or a named sport. Compare the relative efficiency of
this ATP production with anaerobic routes.
(10 marks)
13
JUNE 2002
No Questions.
JANUARY 2003
1
In many activities in Physical Education and Sport, performers will use all three
energy systems and a range of energy fuels.
a) Fig. 1 show the relationship of the energy systems utilised over a one-mile race by
a top class performer.
B
100
Aerobic
90
%
Intensity 80
of
Process 70
A
Energy System Y
60
50
40
30
ATP/PC
Resting 20
Level
10
0
0
i)
1
2
Time (mins)
3
4
Fig. 1
Identify energy system Y and outline the physiological processes
occurring in the body between points A and B on the graph
(3 marks)
14
c)
Fig. 2 shows that exercise intensity and exercise time determine the type of
fuel utilised for energy creation.
100
% Energy
from Fat/
80
Carbohydrates
60
Carbohydrates
40
20
Fats
0
0
20
40
60
80
100
Exercise Intensity (% VO2 max)
70
65
% Fat/
60
Carbohydrate 55
Metabolism 50
45
`
40
35
30
Fats
Carbohydrates
0
20
40
60
80
100
Exercise Time (min)
Fig. 2
Using Fig. 2, explain how intensity and duration of exercise play such an important role in
the type of food fuel we use.
(6 marks)
JUNE 2003
No Questions.
JANUARY 2004
1
b)
A cool down helps to return the body to its resting state by oxidising lactic
acid and lowering heart rate.
i)
2
c)
Describe the energy system that causes a build up of lactic acid in
the body.
(5 marks)
Performers may use the ATP/PC system during short, sharp explosive
movements. Outline the advantages and disadvantages of this energy
system.
(7 marks)
15
JUNE 2004
1
During a competitive team game a performer will use a combination of the three
energy systems.
a)
(i)
Name an energy system. Identify the missing information A, B, C
and D in the table below for your chosen energy system.
(4 marks)
Site of Reaction
Fuel Used
Active Enzyme
A
B
C
(ii)
Molecules of ATP
Produced
D
What is meant by the term Energy Continuum? For the energy
system you selected in (i), identify a situation in a team game when
this system would be predominant. Explain your answer.
(5 marks)
JANUARY 2005
1
a)
Define the terms energy, work and power, giving the units of measurements
for each.
(3 marks)
b)
ATP is a most important compound.
Explain why ATP plays such a major role during physical activity.
(3 marks)
c)
A trained athlete can perform at a higher percentage of their VO2 max
before reaching OBLA than an untrained person.
(i)
2
c)
Explain OBLA.
(3 marks)
The body uses oxygen during the recovery from exercise resulting in an
elevated rate of aerobic respiration. The first stage of this process involves
the breakdown of glycogen to pyruvic acid.
Describe the remaining stages that use oxygen to complete the breakdown
of glycogen.
(8 marks)
JUNE 2005
1
b)
Performers usually rely on all three energy systems for ATP resynthesis.
However, at any one time one energy system may be predominant.
Sketch a graph to show how the predominant energy system depends on
duration of exercise.
(4 marks)
2
c)
Two tests designed to evaluate the strength in the rectus abdominis muscle
are Maximum number of sit ups in 30 seconds and Time until exhaustion in
the Abdominal Curl Sit Up Test.
Identify the type of Strength being evaluated and the Energy System being
used in each of the tests.
(6 marks)
16
JANUARY 2006
No Questions.
JUNE 2006
1
a)
Fig. 1 shows the changes in ATP and PC during a 100m sprint
Sprint Exercise
100
x
80
% of
Resting
Value
x
x
x
x
ATP
x
60
x
40
x
20
Exhaustion
PC
0
0
2
4
6
8
10
12
14
Time (s)
Fig. 1
(i)
The table below describes the predominant energy systems being
used in the 100m sprint.
Identify the missing information X and Y.
Type of Reaction
Fuel Used
Site of Reaction
Anaerobic
PC
X
(ii)
2
c)
(2 marks)
Controlling
Enzyme
Y
Using the graph above, explain the relationship between ATP and
PC levels during the 100m sprint.
(4 marks)
During a match, a games player will work at different intensities and
produce energy from both aerobic and anaerobic pathways. This will affect
the energy system and the fuel used. For example, when a Basketball
player slam-dunks the ball into the basket, they are using the ATP/PC
system and the chemical fuel, Phosphocreatine.
Using examples from a sport of your choice, explain when and why a
performer uses the Lactic Acid and the Aerobic energy systems and fuels
during a competitive match.
Discuss the effects of level of aerobic fitness, availability of oxygen and
food fuels on the efficiency of the aerobic energy system. (13 marks)
17
JANUARY 2007
b)
If the workload was increased during the interval training session, the
performer would reach onset of blood lactate accumulation (OBLA).
(i)
c)
Define OBLA and describe its effect on the skeletal muscle.
(3 marks)
Explain the principle of a coupled reaction using the ATP/PC system as
your example.
(4 marks)
JUNE 2007
2
c)
Fig.2 represents the energy systems used by high-level performers in their
specialist events.
ATP/PC
Lactic Acid
Aerobic
a) 100m sprinter
b) Marathon runner
c) Football goalkeeper
Sketch a similar model to show the energy systems being used by team
player, other than a goalkeeper, in a team game of your choice. Using
examples from the game situation, explain when and why your performer
uses each of the three energy systems.
(8 marks)
18
JANUARY 2008
1
a)
Knowledge of the three energy systems underpins exercise and sport
physiology.
(i)
Energy System
FUEL USED
A
(ii)
Name an energy system and identify the missing information A, B
and C for this system.
(3 marks)
__________________________________
SITE OF REACTION
B
CONTROLLING ENZYME
C
Sketch a graph of energy supplied against time to show when each
of the three energy systems is predominant in relation to duration of
exercise.
(3 marks)
JUNE 2008
2
c)
Swimmers often rely heavily on the use of the lactic acid system for ATP
resynthesis.
Describe the lactic acid system and discuss the advantages and
disadvantages of using this system.
(8 marks)
JANUARY 2009
1
b
(ii)
An average time for completion of an agility test is 17 seconds for
males and 19 seconds for females.
Identify the two predominant energy systems that would be used by
an average performer during the completion of this test.
Discuss the advantages and disadvantages of one of the energy
systems you have identified.
(6 marks)
19