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Optimising performance and evaluating
contemporary issues within sport
UNIT
3
Section A: Applied physiology to optimise performance
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2
Introduction
Central to our study of exercise physiology is
energy. As exercise physiologists we are interested
in where we get the energy to exercise from, how
we can optimise our energy usage during exercise
and how we can recover our energy stores following
exercise. In this chapter we will look at how the body
converts energy from food into energy for muscular
contractions which enable us to run, jump, throw
or indeed perform any number of movements used
in sporting activity. We will examine the energy
requirements of a number of activities ranging
from a gymnastic vault to marathon running
and determine how the intensity or duration of a
particular activity can impact upon how the body
supplies energy. Perhaps most importantly we will
discover how a knowledge of energy supply can help
both coach and athlete maximise performance.
Defining energy
Energy exists in a number of different forms. Electrical,
heat and light energy are just some of the forms that
we all use on a daily basis. Energy is never lost, it is
constantly recycled, often being transferred from one
form to another. When boiling a kettle, for example,
electrical energy is transformed into heat energy.
–the sources, supply and recovery of energy in the body
Energy systems
ChapteR
1
By the end of this chapter you should be able to:
define energy
identify the sources and locations of energy within
the body
explain the role of ATP in providing energy for movement
identify the predominant energy system used related
to the type, duration and intensity of exercise for a
given activity
compare the effectiveness of the ATP-PC, lactic acid
and aerobic systems
identify the chemical/food fuel used, the site of the
reaction, the controlling enzymes, the energy yield and any
by-products produced for each of the energy pathways
explain the term ‘energy continuum’ in context of a
range of physical activities
explain how the body recovers from exercise with
reference to the excess post-exercise oxygen
consumption (EPOC)
explain the fast and slow components of the recovery
process
define VO2
max and its role in limiting performance
define and explain the relationship between VO2
max
and OBLA (onset of blood lactate accumulation).
Key terms
Energy:
the capacity of the body to perform work
Adenosine triphosphate (ATP):
the energy currency of cells. ATP is the only direct
source of energy for all energy requiring processes in
the body
Learning OBJECTIVES:
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Adenosine P P
Pi
Adenosine diphosphate
Inorganic
phosphate
Energy
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Adenosine P P
P
3
energy systems
Similarly, energy found in the chemical bonds of
food fuels that we eat is transformed into mechanical
energy enabling us to move and participate in sporting
activity. It is this conversion of chemical energy into
mechanical and heat energy that is of particular
interest to the sports physiologist and forms the basis
of discussion for the rest of this chapter.
Sources of energy in the body
You will recall from your AS studies that for
movement to occur chemical energy must be
transferred into mechanical energy. Chemical
energy in the body is stored in an easy access,
energy-rich compound called adenosine
triphosphate (ATP). ATP exists in all cells and
consists of a number of atoms held together by high
energy bonds. It is through breaking down these
bonds that energy is released for those processes in
the body that require energy.
Because some of the energy is given off as heat this
reaction is termed exothermic.
There is only a limited supply of ATP within the
muscle cell, probably only enough to perform, for
example, a maximal weight lift in the weights gym or
a sprint start for 2 or 3 seconds. This is because if we
were to have an unlimited supply of ATP we would
have to carry around a supply equivalent to our own
body weight in order to meet the body’s daily energy
requirements! This is obviously not very practical,
so the body has adapted to become a green recycling
machine. ATP is constantly recycled to ensure a
continuous supply of energy. However recycling or
resynthesising of ATP itself requires energy and this
energy is acquired from the food that we eat.
Exam tip:
Make sure you can give the correct units of measurement
of energy. Energy can be measured in calories (kcal) or
joules (J); 1 calorie = 4.184 joules
Fig 1.01 The structure of ATP
Fig 1.03 The body is
a very effective green
machine, as ATP needs
constant recycling or
recharging. We typically
get the energy to recycle
ATP from the foods that
we eat.
Fig 1.02 The breakdown of ATP by ATPase
When energy is required, the enzyme ATPase is
released which initiates the breakdown of ATP. It is
the outermost bond of ATP that most interests ATPase
as it is this bond that stores most energy. Through
the breakdown of ATP energy is released leaving
Adenosine Diphosphate (ADP) and an inorganic
phosphate (Pi), which is illustrated in Fig.1.02.
This reaction can be summarised as follows:
Adenosine Adenosine Inorganic
triphosphate diphosphate
+
phosphate
+ Energy
ATP ADP + Pi + Energy
REMEMBER!
Through the breakdown of ATP, energy is released to
enable the muscles to contract, the heart to beat, and the
brain to fire electrical impulses.
ATP – LIKE A RECHARGEABLE BATTERY
CHARGED
UNCHARGED
TIME FOR A
RECHARGE
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Glycogen Fatty acids
+ glycogen
PC
Time
%fuelused
10 secs 20 mins
applied physiology to optimise performance
4
The fuels for ATP resynthesis are derived from the
following sources:
• Phosphocreatine: Phosphocreatine (PCr)
is used to resynthesise ATP in the first 10
seconds of intense exercise. To help facilitate
this immediate resynthesis of ATP, PCr is stored
within the muscle cell itself alongside ATP.
However, stores of PCr are limited. Good dietary
sources of creatine include red meat and fish.
• Glycogen (stored carbohydrate): Glycogen is
stored in the muscles (350g) and liver (100g). It
is first converted to glucose before being broken
down to release the energy for ATP resynthesis.
During high intensity exercise glycogen can be
used without the presence of oxygen (anaerobic
metabolism). However much more energy
can be released from glycogen during aerobic
metabolism when oxygen is available. Stores of
glycogen are maintained through eating complex
carbohydrates such as pasta and porridge oats.
• Triglycerides (muscular stores of fat): At rest
up to two-thirds of our energy requirement is
met through the breakdown of fatty acids.
This is because fat can provide more energy per
gram than glycogen (1g of fat provides 9.1kcal
of energy compared to 4.1kcal of energy for
every 1g of glycogen). In spite of the fact that fat
requires about 15% more oxygen than glycogen
to metabolise it remains the favoured fuel source
at rest and during endurance-based activity.
Fats can only be used as an energy source when
there is a plentiful supply of oxygen and must be used
in conjunction with glycogen. This is because the
transport of fatty acids in the blood is poor (and slow!)
due to their low solubility. Consequently fatty acids do
not arrive at the muscle cell in sufficient quantities to
sustain muscle contraction on their own. Glycogen
must therefore provide the supplementary energy.
• Proteins: Protein is the least favoured source
of energy, only contributing 5–10% of the total
energy yield. In the presence of oxygen, protein
is used as an energy provider, usually when
stores of glycogen are low. Good dietary sources
of protein include meat, fish and dairy products.
You will recall that protein’s primary function is
to facilitate the growth and repair of the body’s
cells, including muscle tissue.
Key terms
Exothermic reaction:
a chemical reaction that releases energy
Phosphocreatine:
a high energy compound which exists in the muscle
cells alongside ATP and provides the energy for ATP
resynthesis when the intensity of exercise is very high
Anaerobic metabolism:
the release of energy through the breakdown of food
fuels in the absence of oxygen
Aerobic metabolism:
the release of energy through the breakdown of food
fuels in the presence of oxygen
Key terms
Fatty acids:
the component of fat used for energy provision
REMEMBER!
There is only sufficient ATP stored within the muscle cell
to perform high intensity activity for 2 or 3 seconds.
Fig 1.04 Sources of energy for ATP resynthesis against time
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energy systems
5
REMEMBER!
When exercising at higher intensities, the body will rely
more upon glycogen as a source of fuel.
REMEMBER!
The source of energy for ATP resynthesis is
dependent largely upon the intensity and duration of
the sporting activity.
The conversion of these fuels into energy which can
then be used to resynthesise ATP occurs through
one of three pathways or energy systems. It is the
intensity and duration of the exercise that dictates
whether oxygen is present and ultimately which
energy system predominates.
The three energy systems are:
1. the aerobic (oxidative) system
2. the lactic acid or lactate anaerobic system
3. the ATP-PC or alactic system.
The more intense the activity (e.g. the harder the
athlete is working, signalled perhaps by a higher
heart rate) the more the performer will rely on the
production of energy from anaerobic pathways
such as the ATP-PC system or lactic acid system. As
exercise intensity decreases and endurance increases
the more the athlete will rely on the aerobic system
for providing the energy to resynthesise ATP.
As most of our daily energy requirements are
supplied by the aerobic system, it is this system we
will visit first.
The aerobic (oxidative) energy
system
During resting conditions or during exercise where
the demand for energy is low, oxygen is readily
available (hence the name aerobic system) to release
stored energy from muscle glycogen, fats and
proteins. The aerobic system is the body’s preferred
energy pathway as it is by far the most efficient in
terms of ATP resynthesis. In fact the energy yield
from aerobic metabolism is 18 times greater than
that gained from anaerobic processes.
During times where there is a plentiful supply of
oxygen (i.e. oxygen supply exceeds oxygen demand)
glycogen is first converted to glucose-6-phosphate
before it is broken down into pyruvate (pyruvic acid).
This all takes place in the sarcoplasm of the muscle
cell and results from the actions of the enzyme
phosphofructokinase (PFK) and is illustrated as the
first few stages in Figure 1.07.
Under anaerobic conditions pyruvic acid
(pyruvate) is converted into fatigue-inducing lactic
acid by the enzyme lactate dehydrogenase (LDH).
However when oxygen is in rich supply, pyruvic
acid is instead converted into acetyl-coenzyme-A
by combining with the enzyme pyruvate
dehydrogenase. The site for energy release now
moves to specialised parts of the cell known as
mitochondria. These industrious units are in
abundance within the muscle and manufacture
energy for ATP resynthesis by facilitating the many
chemical reactions required to completely break
down our stores of glycogen and fats to ensure
a continuous supply of energy. Because of their
ability to supply lots of energy mitochondria are
particularly found in large numbers in slow twitch
muscle fibres.
Fig 1.05 illustrates a mitochondrion. You can
see from this diagram that there are two key stages
of the aerobic system that take place within the
mitochondria: the Krebs cycle and the electron
transport system.
Task 1.01
Keep a diary of all the food and drink that you
consume in one day.
From the packaging calculate how much energy
you have consumed in both calories (kcal) and
Joules (j).
TIP – You may need to measure out quantities of
foodstuffs to give an accurate picture of your
energy intake.
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Outer
membrane
Inner membrane
Matrix
(Krebs cycle occurs here)
Cristae
(electron transport
system takes
place here)
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The Krebs cycle
The Krebs cycle takes place in the fluid-filled matrix
of the mitochondria which has a rich supply of
enzymes that are ready to perform the necessary
chemical reactions to help release the remaining
energy stored within the molecule.
Three significant events occur at this stage.
1. Oxidation of citric acid. This involves
the removal of hydrogen atoms from the
compound which enter the final stage of the
aerobic system; the electron transport system.
2. Production of carbon dioxide. The
removal of hydrogen means that only carbon
and oxygen remain. These combine to form
carbon dioxide which is carried around to the
lungs where it is breathed out.
Fig 1.06 A race walker will utilise the aerobic system
to provide energy for muscular contractions
Key terms
Mitochondrion:
the powerhouse of the cell. Mitochondria are
specialised structures within all cells that are the site of
ATP production under aerobic conditions
Krebs cycle:
a series of chemical reactions that occur in the matrix
of the mitochondria yielding sufficient energy to
resynthesise 2 ATP molecules and carbon dioxide.
It forms part of the aerobic system
Electron transport system:
a series of reactions in the cristae of the mitochondria
where the majority of energy is yielded for ATP
resynthesis. 34 moles of ATP can be resynthesised from
just 1 mole of glycogen at this stage of the aerobic system
Mole:
an amount of a substance that contains a
standardised number of atoms (6.0225 x 10²³ known
as Avogadro’s number)
REMEMBER!
Slow twitch muscle fibres house many more mitochondria
than fast twitch fibres and hence are more suited to
aerobic activity such as marathon running.
REMEMBER!
The aerobic system is of particular use to athletes who
need to perform relatively low intensity exercise for a
long period of time. A triathlete or marathon runner are
obvious examples.
Fig 1.05 A mitochondrion
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Glycogen (C6H12O6)
Glucose-6-phosphate
Pyruvic acid
Acetyl-coenzyme-A
Citric acid
Krebs cycle
Sarcoplasm
(anaerobic
glycolysis)
Insufficient O2
Lactic acid
(2C3H6O3)
2ATP
LDH
2ATP
CO2
Electron transport
system
34 ATP
H+ eH+
e-
H2O
O2
H
O2
ß oxidation
Fatty acids
Mitochondria
energy systems
7
Fig.1.07  ATP resynthesis via the aerobic system
	 3.	Resynthesis of ATP. Sufficient energy is
released at this stage to resynthesise 2 moles
of ATP
The electron transport system
This final stage of glycogen breakdown occurs in
the cristae of the mitochondria. Hydrogen given
off at the Krebs cycle stage is carried to the electron
transport system.
There are two important features of this stage of
the aerobic pathway:
	 1.	Water (H2
O) is formed when the hydrogen
ions (H+) and electrons (e-) combine with
oxygen through a series of enzyme reactions.
	 2.	Resynthesis of ATP: By far the majority
of energy is released here for the resynthesis
of ATP. In fact 34 moles of ATP can be
resynthesised, making this by far the most
efficient source of energy in the body.
Other fuels used in aerobic energy
production
So far we have only focused our attention on the
aerobic breakdown of glycogen. However fat and
protein can also be metabolised under aerobic
conditions to form CO2
, H2
O and energy for ATP
resynthesis. Fats stored in the muscle as triglycerides
must first be broken down into glycerol and free fatty
acids (FFAs) before they go through the process of
beta(ß)-oxidation (the fat equivalent of glycolysis).
Following beta-oxidation fatty acids can enter the
Krebs cycle where they can then follow the same
path of metabolism as glycogen. The main difference
between fat and glycogen metabolism, however, is
that substantially more energy (for ATP resynthesis)
can be elicited from one mole of fatty acids than
from one mole of glycogen. Consequently, fatty
acids become the preferred fuel as the duration of
exercise increases. Typically this occurs after 20
minutes of sub-maximal activity. This has important
consequences for endurance performers as it
enables them to spare their glycogen for later in the
event or competition, when intensity of the exercise
might increase.
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Glycogen Triglycerides Protein
Krebs
cycle
Oxidised
by the
heart, liver
and
skeletal
muscle
Exhaled by
lungs
Electron transport
system
with
oxygen
without
oxygen
H+
Glucose Fatty acids Amino acids
Acetyl-co-APyruvic acid
Lactic acid
La-
e-
Buffered
in the
blood and
muscle
CO2
ATP
H+
H20
+ oxygen
ATP
ATP
applied physiology to optimise performance
8
Advantages to the athlete of using the
aerobic system
•	 Significantly more ATP can be resynthesised
under aerobic conditions than anaerobic (36 ATP
aerobically compared to 2 ATP anaerobically –
from one mole of glycogen).
•	 The body has substantial stores of muscle
glycogen and triglycerides to enable exercise to
last for several hours.
•	 Oxidation of glycogen and fatty acids do not
produce any fatiguing by-products.
Drawbacks of this system to
the athlete
•	 When we go from a resting state to exercise it takes
a while for sufficient oxygen to become available to
meet the new demands of the activity and enable
the complete breakdown of glycogen and fatty acids.
Consequently this system cannot provide energy
to resysnthesise ATP in the immediate short term
(unless the activity is of particularly low intensity)
or during higher intensity activity
•	 Although fatty acids are the preferred fuel
during endurance events such as a marathon,
the transport of fatty acids to the muscle is slow
and requires about 15% more oxygen than that
required to break down the equivalent amount of
glycogen.
•	 Due to the low solubility of fatty acids the
endurance athlete will usually use a mixture
of both glycogen and fatty acids to provide the
energy for ATP resynthesis. When glycogen
becomes depleted and the body attempts to
metabolise fatty acids as a sole source of fuel,
muscle spasms may result. This is commonly
known as hitting the wall.
Fig 1.08  A summary of ATP resynthesis from the three main energy providing nutrients
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energy systems
9
The complete breakdown of one mole of glycogen
can be summarised as follows:
C6
H12
O6
+ 6O2
6CO2
+ 6H2
O + ENERGY
Energy + 38ADP + 38Pi 38ATP
Task 1.02
During a 10,000m race the aerobic system will be used for the majority of the event to resysnthesise ATP.
Complete the table below with the required information.
Site of reaction Fuels used Active enzymes Molecules of ATP produced
Aerobic system (oxidative)
The aerobic system and recovery
The recovery process is concerned with returning
the body to its pre-exercise state so that heart rate,
oxygen consumption, blood lactate levels and
glycogen stores are at exactly the same levels as they
were before the exercise commenced!
You will know from your own experience that
whatever the exercise you may have performed,
whether it be a maximal lift in the weights room or
a 5km run, the recovery period involves a period
where breathing and heart rates are elevated. This
occurs because all recovery is dependent upon the
consumption of oxygen, and the elevated respiratory
and heart rates ensure that adequate amounts of
oxygen are taken into the body and delivered to
the muscles to enable a swift recovery. The oxygen
delivered to the muscles will help rebuild stores of PC
and ATP as well as remove any lactic acid that may
have accumulated during the activity.
Key terms
Recovery:
the return of the body to its pre-exercise state
REMEMBER!
As recovery can only occur when there is sufficient
oxygen available then it is often associated with the
aerobic energy system.
Task 1.03
An investigation to examine recovery heart rate
response to varying intensities of exercise.
Equipment: heart rate monitor, stop watch,
gymnastics bench, metronome. (If you do not have
access to a heart rate monitor then record your heart rate
at the carotid artery for a 10 second count and multiply
by 6 to convert to beats per minute.)
1. Record resting heart rate at the beginning of the class.
2. Record heart rate just prior to exercise.
3. Commence exercising by stepping onto and off the
bench in time with the metronome that has been set
at a low intensity.
4. Record your heart rate after one, two and three
minutes of exercise. After the third minute of exercise
stop the test. Continue to record your pulse each
minute during recovery.
Time Exercise intensity
Low Medium High
Resting HR
HR prior to exercise
Exercise 1 min
Exercise 2 min
Exercise 3 min
Recovery 1 min
Recovery 2 min
Recovery 3 min
Recovery 4 min
Recovery 5 min
Recovery 6 min
Recovery 7 min
Table 1.01 Example table: copy out a similar one for this task
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0 1 2 3 1 2 3 4 5 6HR prior
to exercise
HR(bpm)
Exercise Recovery
Time (mins)
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10
Excess post-exercise oxygen
consumption (EPOC)
Excess post-exercise oxygen consumption
represents the extra volume of oxygen consumed
following exercise that enables the body to fully
recover and return to its pre-exercise state.
At the very beginning of exercise (even at low
intensities) or when exercise is of high intensity it is
likely that the body will need to work anaerobically
for a period of time as there may be insufficient
oxygen available to use the aerobic energy system
exclusively to provide the energy for muscular work,
i.e. a deficit occurs in the oxygen supply. The oxygen
deficit thus represents the amount of extra oxygen
required to enable the entire activity to be completed
using the aerobic energy system. Since it takes a
while for the aerobic system to ‘kick in’ and provide
the muscles with energy at the beginning of activity,
a deficit will always develop.
Researchers have identified two stages
of recovery:
• Stage 1: The fast replenishment stage
(formerly referred to as the alactacid debt)
• Stage 2: The slow replenishment stage
(formerly known as the lactacid debt).
Task 1.03 continued
5. Once your heart rate has returned to its
resting value (or within a few beats) repeat the
test at a medium intensity. Record your results
as before.
6. Repeat the exercise for a third time but at very high
intensity. Once again record your results.
7. Now use your results to plot a graph for each of the
three workloads. Plot each graph using the same
axes placing heart rate along the y axis and time
along the bottom x axis. Don’t forget to show your
resting heart rate values on the graph.
8. For each of your graphs explain the pattern of
recovery heart rate.
NB: The length of the recovery period depends upon
the intensity and to a lesser degree the duration of
the previous exercise.
Fig. 1.09 Example graph: copy out a similar one on graph paper
REMEMBER!
The term oxygen debt was often used to explain the
restoration of ATP and PC and removal of lactic acid
during recovery. But this failed to explain the extra oxygen
needed during recovery to restore muscle oxymyoglobin
and to keep respiratory and heart rates elevated. EPOC
is therefore the preferred term now and the oxygen debt
viewed as one part of this process.
Task 1.04
Examine the graphs you drew in Task 1.03.
Can you identify a fast and slow stage of oxygen
consumption during the recovery phase? If so shade
these stages on the graph and label them ‘fast stage’
and ‘slow stage’.
Key terms
Excess post-exercise oxygen
consumption (EPOC):
the volume of oxygen consumed during recovery above
that which normally would have been consumed at rest
during the same period of time
Oxygen deficit:
the volume of extra oxygen required to complete the
entire activity aerobically
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Slow component
• Removal of lactic acid
• Maintenance of elevated heart
and respiratory rates
• Replenishment of glycogen
stores
• Elevated body temperature
Fast component
• Restoration of muscle ATP
+ PC
• Re-saturation of myoglobin
with oxygenExcess
Post – exercise
Oxygen
Consumption
Key terms
Fast replenishment:
the first component of EPOC. Oxygen consumed is
used to resaturate myoglobin and resynthesise ATP and
PC. It takes approximately 2–3 minutes
Slow replenishment:
the second component of EPOC. Oxygen consumed
during this stage is largely used to remove lactic acid
which takes about 1 hour. In addition oxygen is also
used to maintain cardiac and respiratory rates and
normalise body temperature
'
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EPOC/ALACTACID DEBT
(Fast replenishment)
EPOC/LACTACID DEBT
(Slow replenishment)
Exercise Recovery
Time (min)
Time (min)
Exercise Recovery
Oxygen
deficit
Debt
VO2litre/min
Rest
Fast
Fast Slow
'VO2litre/min
Rest
Steady state (oxygen
supply = oxygen demand)
Oxygen
deficit
energy systems
11
a)
b)
Fig 1.10 Oxygen consumption during and following
(a) a sub-maximal task and (b) maximal task
REMEMBER!
1. You will notice from Figure 1.10a that the volume of
EPOC is greater than the volume of oxygen deficit.
This is because the ‘muscles’ of recovery such as the
heart and respiratory muscles require oxygen to keep
breathing and heart rates elevated.
2. You will note from Figure 1.10b that the 2 stages of
recovery are clearly visible following maximal or high
intensity exercise. However following sub-maximal
or low intensity exercise only the fast stage may be
evident. This is because the majority of the work has
been completed aerobically and little lactic acid has
accumulated during the exercise.
The fast replenishment stage
This is the first stage of the recovery process and
relates to the immediate consumption of oxygen
following exercise. Its primary function is to
re-saturate myoglobin with oxygen and provide
aerobic energy to resynthesise adenosine
triphosphate (ATP) and phosphocreatine (PC).The
fast stage of recovery is usually completed within
2–3 minutes and utilises up to 4 litres of oxygen.
Fig. 1.11 The components of excess postexercise
oxygen consumption (EPOC)
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1 2 3 4
10
secs
Exercise Recovery
Time (min)
%Musclephosphagen
storesreplenished
100
75
50
25
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12
Fig 1.12 The replenishment of muscle phosphagens following
maximal exercise
The slow replenishment stage
The slow replenishment stage of EPOC can take up
to 2 hours and utilises between 5 and 10 litres of
extra oxygen depending upon the intensity of the
preceding exercise.
The oxygen consumed during the slow stage of
recovery has several functions:
• Removal of lactic acid: Lactic acid accumulated
during exercise must be removed if the body is to
recover fully. You will recall that most lactic acid
is converted back into pyruvate and then into
CO2
and water, the remainder being converted
into muscle glycogen, blood glucose and protein.
Much of the oxygen consumed during this stage is
therefore used to provide the energy to enable this
removal of lactic acid to take place. Typically the
oxidation and removal of lactic acid takes about
an hour, but this can be accelerated by performing
a cool down. The cool down or active recovery
helps keep the metabolic activity of the muscles
high and the capillaries dilated so that oxygen can
be flushed through the muscle tissue oxidising
and removing any lactic acid accumulated.
REMEMBER!
50 per cent of PC stores are restored within the first 30
seconds of recovery!
• Maintenance of elevated heart and
respiratory rates: Like all muscles, the
muscles of the respiratory system and the heart
require oxygen to provide energy for them to
work continuously. During the recovery period
extra energy is required to keep the heart and
respiratory rates elevated above resting levels.
This is so the lungs can take in plenty of oxygen
which can then be pumped around the body by
the heart to the working muscles to re-saturate
myoglobin, resynthesise muscle phosphagens
(ATP and PC) and remove lactic acid.
• Replenishment of muscle glycogen stores:
During all types of exercise it is likely that some
muscle glycogen stores will become depleted. It
is in the interests of the performer to replenish
these stores as soon after exercise as possible.The
replenishment of these muscular stores of glycogen
is largely dependent upon two key factors:
1. The type of exercise that has been performed
2. The amount and timing of carbohydrate
consumption following exercise.
REMEMBER!
The best time to consume a post-exercise meal is as
soon as is practical following the activity. The rate of
muscle glycogen replacement is significantly quicker
during the first 45–60 minutes. This is known as the
carbohydrate window.
First of all let us consider the type of exercise
performed. Studies have suggested that following
continuous, endurance-based activity little
glycogen is restored in the period immediately
following activity. Complete muscle glycogen
repletion can take up to 48 hours in this instance.
During high intensity, short duration activity,
however, a significant amount of muscle glycogen
can be resynthesised within 30 minutes to one hour
immediately following exercise (probably due to
conversion of lactic acid back into glycogen via the
cori cycle) and complete resynthesis requires a 24hour
recovery period.
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16
14
12
10
8
6
4
2
Passive recovery
Active recovery
Resting level
0 20 40 60 80 100 120
Bloodlactate(mmol/litre)
Recovery (min)
Exercise
periodRest Recovery period (min)
0 4 8 12 16
4
3
2
1
0
VO2litre/min'
E
C
A
D
B
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13
REMEMBER!
A 400m runner will consume a large volume of oxygen
during the slow replenishment stage as a large amount of
lactic acid will have accumulated in their muscles.
The second key factor concerns the amount of
carbohydrate consumed following exercise. Muscle
glycogen repletion occurs more rapidly when a high
carbohydrate meal is consumed within the first 45–60
minutes following exercise: this is commonly known
as the carbohydrate window. A high carbohydrate
meal should consist of 200–300g of carbohydrate.
• An elevated body temperature:You have
probably all experienced the increase in body
temperature that accompanies all exercise whether
it is a maximal all-out effort on the bench press
or a 5Km run. This increase in body temperature
generally results from the increased metabolic
Fig 1.13 The effect of cool down or active recovery on
recovery time following a bout of high intensity work
activity of the body which provides the energy to
perform work. However with every 10° increase in
body temperature the metabolic activity of the cells
doubles. Oxygen is needed to feed this increase even
during the recovery period and continues to do so
until the body has cooled right back down to normal
resting temperatures. The oxygen for this comes
through the slow replenishment stage of EPOC.
Note that blood lactate levels return towards normal resting
levels much quicker when a period of active recovery has
taken place.
REMEMBER!
The exercise intensity during a cool down that best removes
lactic acid is between 30–45% VO2
max for untrained
subjects and 50–65% VO2
max for trained performers.
Key terms
Active recovery:
a recovery period during which time light exercise is
performed
Rest recovery:
a recovery period during which time the performer has
rested passively
Cori cycle:
the process where lactic acid is taken to the liver for
conversion into glucose and glycogen
Task 1.05
Figure 1.14 is often used to illustrate EPOC.
1. From the graph state what each of the
letters A–E represents.
2. For what is the oxygen consumed during
part ‘D’ used?
3. Which letters can be used to determine
EPOC?
Fig 1.14 Oxygen consumption during exercise and recovery
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applied physiology to optimise performance
14
endurance performance we need a big and efficient
pump to deliver oxygen-rich blood to the muscles
and we need mitochondria-rich muscles to use the
oxygen and enable high rates of exercise.
VO2
max or maximal oxygen uptake can therefore
be defined as:
‘…the maximum volume of oxygen that can be utilised
or consumed by the working muscles per minute…’
A high VO2
max, or maximal oxygen uptake, is
indeed one of the hallmark characteristics of
great endurance performance in activities such as
swimming, cycling, rowing and running. However,
it is elite cross country skiers that are considered
the most powerful in oxygen uptake capacity. This is
probably because cross country skiing engages just
about all of the major muscle groups of the body.
This is not, however, the only determining factor of
VO2
max.
The ability of the muscles to consume the
greatest amount of oxygen as possible the body is
dependent upon two further key factors:
1. An effective oxygen delivery system that brings
oxygen from the atmosphere into the working
muscles
2. An aerobic-friendly muscle structure which
possesses a large volume of myoglobin and a high
density of mitochondria which can be used to
produce ATP via the aerobic energy system.
Maximal oxygen consumption
(VO2
max)
Lance Armstrong’s is VO2
max reported as 83.8ml/
kg/min, Paula Radcliffe’s an amazing 80ml/kg/
min and Matt Pinsent has the highest ever recorded
in the UK at a staggering 8.5 litres/min! What do
these figures represent? Well it’s their VO2
max of
course! Indeed if you go into the chat rooms of
any marathon running web sites conversation
soon turns to the size of your VO2
max. For effective
Task 1.06
The data in table 1.03 relates to the rate of lactate removal
during recovery from exhaustive exercise following
(i) rest recovery and (ii) active recovery.
1. Draw a graph of % lactate removed against
time using the data in the table.
Briefly explain what the graph shows.
2. On your graph mark off the times for each
type of recovery when 50 per cent of blood
lactate had been removed. What does this
suggest?
3. What type of activity would you suggest a
performer undertake during a period of
active recovery?
% lactate
removed
Recovery time (mins)
(Rest recovery)
Recovery time (mins)
(Active recovery)
20 8 4
40 20 8
60 35 15
80 55 25
100 180 70
Task 1.07
Copy out the following table and complete the
approximate recovery times for each factor
Recovery process Recovery
time
Re-saturation of myoglobin with oxygen
Resynthesis of muscular stores of
ATP and PC
Repayment of fast component of EPOC
Removal of lactic acid:
• with active recovery
• with rest recovery
Repayment of slow component of EPOC
Restoration of muscle glycogen stores
4. What intensity of exercise (measured as a
percentage of VO2
max) would you suggest
the active recovery period is completed for
a) an untrained subject b) a trained performer?
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CO2
O2
ATP
Exhale CO2
Oxygen-poor air
to lungs
CO2 enriched,
O2 depleted blood
returns to heart Exercising muscle
uses oxygen
Oxygen-rich
blood from lungs
to body
Inhale
oxygen-rich air
energy systems
15
Here is an example of a VO2
max treadmill test
using Johnny, a typical A level student as a subject:
1.	 Firstly Johnny is weighed. This is so his VO2
max
can be given relative to his body weight. A simple
reading of ml/min would ignore the fact that
larger people have larger lungs and are capable of
taking in more oxygen into their bodies.
2.	 Following a warm-up, Johnny places a mask over
his mouth which is attached to the computer by
a hose tubing. Johnny begins the treadmill test at
a speed of 10km/h. Whilst running he breathes
through a two-way valve system. The computer
analyses the relative concentrations of oxygen and
carbon dioxide inspired and expired respectively.
From this it is possible to calculate the amount of
oxygen extracted and consumed by the muscles
and the amount of carbon dioxide produced over
time. In order to reach an exhaustion point and
get a maximum reading the treadmill speed is
increased by 1km/h every minute.
3.	 After 2 minutes the speed of running has
increased to 12km/h, the graph below shows
an increase in the level of oxygen breathed in
and carbon dioxide breathed out. The distance
between the two values shows that Johnny is
Fig.1.15  Cross-country skiers reportedly have
the highest VO2
max of all sports performers
Fig 1.16  Oxygen transport and
consumption during exercise
Measuring maximal oxygen
consumption (VO2
max)
You will recall from your AS studies that there
are several tests of maximal oxygen consumption
(VO2
max). These tests are listed below:
•	 The multi-stage fitness test
•	 Harvard step test
•	 PWC170 test
•	 Cooper 12-minute run test.
Whilst the multi-stage fitness test gives a reasonable
prediction of VO2
max it cannot give a truly objective
measure of the volume of oxygen actually consumed
by the working muscles. The only way we can possibly
do this is in a sports science laboratory where direct
gas analysis can take place. In order to determine
an athlete’s true maximal aerobic capacity, exercise
conditions must be created that maximally stress the
blood delivery capacity of the heart.
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6000
5000
4000
3000
2000
1000
0
1 2 3 4 5 6 7 8 9 10 11
10 mins: Amount of oxygen
inhaled reaches its maximum
Time (min)
V'O2 ml / min
V'CO2 ml / min
Volume(ml)applied physiology to optimise performance
16
working aerobically with a good supply of oxygen
to the muscles. He is in steady state where oxygen
demand is being met by oxygen supply.
4. After 7 minutes the speed has increased to 17
km/h and Johnny’s heart rate has increased
significantly to 192 bpm. His breathing rate has
become faster as the levels of carbon dioxide
increase further. Now the level of oxygen begins
to level out. Johnny will have to call on more
and more anaerobic energy to meet any further
extra energy demands as his body struggles to get
oxygen to his muscles.
5. After 10 minutes Johnny is racing along at
20 km/h, his heart is doing overtime at over
200 bpm and his lungs are working at their
maximum to get oxygen into the body. This is the
point where the VO2
max is taken. His reading
is 57.6 ml/kg/min. After nearly 10.5 minutes
Johnny is completely exhausted. He can no
longer exercise and the test is stopped.
6. Johnny’s reading of 57.6 ml/kg/min is good
and shows that he has some capacity to perform
endurance based activity.
Fig 1.17 VO2
max timeline: Johnny’s results
Key terms
Direct gas analysis:
the most valid and reliable method of measuring
VO2
max. During the test, subjects are measured at
progressively increasing intensities on a treadmill, cycle
ergometer or rowing machine. Concentrations of oxygen
and carbon dioxide inspired and expired are monitored
Maximal oxygen consumption (VO2
max):
the maximum volume of oxygen that can be utilised
or consumed by the working muscles per minute. It is
usually measured in ml/kg/min
Key terms
Absolute VO2
max:
a VO2
max value given in litres/min
Relative VO2
max:
a VO2
max value that takes account of bodyweight and
measured in millilitres of oxygen per kg of bodyweight
per minute (ml/kg/min)
REMEMBER!
VO2
max is expressed as a rate, either millilitres per kg of
bodyweight per minute for weight bearing activities such
as running or litres per minute for partial weight bearing
activities such as rowing or cycling.
Task 1.08
Use the following data to plot a bar graph
illustrating the expected VO2
max scores for the
activities shown.
Activity Male
(ml/kg/min)
Female
(ml/kg/min)
Triathlete 80 72
Marathon runner 78 68
Distance swimmer 72 64
Middle distance runner
(800–1500)
72 63
Games player 66 56
Gymnast 56 47
Weightlifter 52 43
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17
Factors affecting maximal oxygen consumption (VO2
max)
Fig 1.18 summarises the main factors that affect an individual’s maximal oxygen consumption.
REMEMBER!
Physiology
The physiological make up of the body will almost certainly affect VO2
max. Below are just a few physiological factors that
contribute to a higher VO2
max score:
* a high percentage of slow twitch (type 1) muscle fibres
* high capillary density
* high mitochondrial density and myoglobin content
* high blood volume and haemoglobin content.
Genetics
Studies on identical and fraternal
twins have suggested that genetics
accounts for 25 to 50 per cent of
VO2
max scores.
It appears that Olympic champions are
born with a unique potential that is
transformed into athletic performance
through years of hard training.
Age
Typically VO2
max will decrease with age. After the age
of 25 years, VO2
max is thought to decrease by about
1 per cent per year. Regular physical activity can slow
down the rate of this decline.
Lifestyle
Smoking, leading a sedentary lifestyle and having
a poor diet can greatly reduce VO2
max values.
Body composition
Research shows that VO2
max scores
decrease as the percentage of body
fat increases. This is because fat is
non-functional weight that must be
carried around. Typically males should
aim for a body fat per cent of between
14–17 per cent whilst females should
aim for a value between 24–29 per cent.
Gender
When we consider absolute VO2
max,
the typical untrained male has a value
of 3.5 litres/min whilst that of a female
is approximately 2l/min – a 43 per
cent difference! When we consider
bodyweight to give a relative value
this difference is reduced to 15 to
20 per cent.
Training
VO2
max can only be improved by
10 to 20 per cent following training.
This is somewhat surprising given the
vast improvement in the delivery and
transport of oxygen resulting from
long-term endurance training. The
best methods of training to improve
VO2
max include continuous training,
Fartlek and aerobic interval training.
Fig 1.18 Factors affecting maximal oxygen consumption (VO2
max)
1. The average VO2
max score for an average ‘A’ level
student should be around 45–55 ml/kg/min for males
and 35–44ml/kg/min for females.
2. Surprisingly, endurance training such as following a
continuous training regime can only improve VO2
max by
between 10 and 20%.
3. When we consider absolute VO2
max the typical
untrained male has a value of 3.5 litres/min whilst
that of a female is approximately 2 litres/min – a 43%
difference! When we consider bodyweight to give a
relative value this difference is reduced to 15–20%.
4. As a rule of thumb when VO2
max is measured in relative
terms (taking bodyweight into consideration) female
athletes have a score of approximately 10ml lower than
comparable males of the same activity group
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applied physiology to optimise performance
18
which elicits energy plus 6 moles of carbon dioxide
and 6 moles of water. Notice that all the oxygen
inspired here is used to form carbon dioxide.
RER =
VCO2
VO2
=
6CO2
6O2
= 1.0
However, when fat is oxidised the oxygen inspired
does not only combine with carbon to form carbon
dioxide but some is also required to combine with
hydrogen to produce water:
C16
H32
O2
(fat) + 23O2
16CO2
+ 16H2
O
So this formula tells us that in order to break down
one mole of fat 23 moles of oxygen is required:
16 moles of which combine with carbon to form
carbon dioxide, the remaining 7 moles combine with
hydrogen to form water.
RER =
VCO2
VO2
=
16 CO2
23 O2
= 0.17
So the metabolism of fat only elicits 70% of the
energy per litre of oxygen consumed than when
compared to carbohydrate. So although fat contains
twice the chemical energy of carbohydrate per
gram, it requires more oxygen to release the energy
stored within it.
Task 1.09
If your absolute VO2
max was measured at
4.0 litres/min and you weighed 75kg, calculate your
relative VO2
max.
Task 1.10
Design a training programme aimed at
improving the VO2
max of a performer. Make sure
you prescribe appropriate methods of training and
clearly state the expected intensity of training.
Exam tip:
Make sure you are able to describe a test of VO2
max. You
must be able to critically evaluate the test commenting on
its validity and reliability.
The respiratory exchange
ratio (RER)
The respiratory exchange ratio is the ratio of
the volume of carbon dioxide expired per minute to
the volume of oxygen consumed per minute and is
used by the coach and athlete as a measure of the
intensity at which the athlete is training.
The respiratory ratio can be assessed as follows:
Respiratory exchange ratio =
Carbon dioxide expired
per minute (VCO2
)
Oxygen consumed per
minute (VO2
)
However, the amount of energy released through the
consumption of every litre of oxygen is dependent
upon the type of food fuel that is metabolised.
You will recall from page 9 that the following
formula can be used to summarise the aerobic
breakdown of glucose (our usable form of
carbohydrate):
C6
H12
O6
(glucose) + 6O2
6CO2
+ 6H2
O + energy
From this equation we can see that to break down
one mole of glucose, 6 moles of oxygen are required
The respiratory exchange ratio is important for the
coach and athlete when planning training, as it can
be used to assess the intensity at which a performer
is working. If the RER is closer to 1 this suggests that
the athlete is working hard and training at a higher
Exam tip:
It is usual to refer to VCO2
/VO2
at cellular level as
the respiratory quotient (RQ) and at lung level as the
respiratory exchange ratio (RER).
Key terms
Respiratory exchange ratio:
a method of determining which metabolic fuel is
predominantly in use during exercise. It is calculated
by analysing oxygen consumption and carbon
dioxide production
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Creatine kinase
Creatine = =
Stage 1 = PCr
breakdown
(exothermic
reaction)
Stage 2 = ATP
resynthesis
(endothemic
reaction)
Stage 3 = ATP
recycled
ready to be
used once more
P
Adenosine
Coupled
reaction
E
AdenosineE P P
P
P P P
energy systems
19
The anaerobic energy systems
The ATP-PC (alactic) system
We have established that muscular stores of ATP
will have depleted after about 3 seconds of maximal
activity. For high intensity activity to continue the
immediate recycling of ATP is necessary. However
the rapid increase in activity results in insufficient
oxygen being available (an oxygen deficit) to
sustain this ATP resysnthesis. The body therefore
relies upon a second energy-rich compound found
alongside ATP in the muscle cells. This compound is
phosphocreatine (PCr).
Like ATP the breakdown of phosphocreatine
takes place in the sarcoplasm of a muscle cell
and is facilitated by the enzyme creatine kinase.
The release of creatine kinase is stimulated by the
increase in ADP and inorganic phosphates (both
products of ATP breakdown)
PCr Creatine + Pi + energy
intensity as more carbohydrate is being used as a
metabolic fuel. Conversely, if the RER is closer to
0.7 then the body is relying more heavily on fat as a
metabolic fuel and the intensity of the training will
be comparatively lighter.
REMEMBER!
The respiratory exchange ratio can only be assessed
under laboratory conditions where the consumption of
oxygen and the production of carbon dioxide can be
analysed through direct gas analysis.
Fig 1.19 The ATP-PC system as a coupled reaction
The coupled reaction
Because PCr exists alongside ATP in the sarcoplasm
of the muscle cell, as rapidly as energy is released
from ATP during exercise it is restored through the
breakdown of PCr. This linked reaction more or less
occurs simultaneously and It takes one molecule of
PCr to recycle one molecule of ATP.
Advantages of this system to
the athlete
• The most important feature of this system is that
ATP can be resynthesised very rapidly (almost
immediately) by PCr.
• PCr stores are recovered very quickly, within 2–3
minutes of exercise stopping. This means that high
intensity exercise can once again be undertaken.
• It is an anaerobic process and so does not need to
wait for the 3 minutes or so for sufficient oxygen
to be present.
• There are no fatiguing by-products which could
delay recovery.
• Some athletes may seek to extend the time that
they can use this system through creatine
supplementation.
Unlike ATP, the energy released from the breakdown of
phosphocreatine is not used for muscle contraction but
is instead used to recycle ATP, so that it can once again
be broken down to maintain a constant energy supply.
Energy
+ ADP + Pi ATP
(from PCr breakdown)
As energy is required for this reaction to take place it
is known as an endothermic reaction.
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ATP
PC store
Time (seconds)
ConcentrationofATP/PC
applied physiology to optimise performance
20
Drawbacks of this system to
the athlete
• The main drawback is that there is only a limited
supply of PCr stored in the muscle cell, sufficient
only to resynthesise ATP for approximately 10
second or so. Fatigue occurs when concentrations
of PCr fall significantly and can no longer sustain
ATP resynthesis.
• Resynthesis of PCr can only take place when
there is sufficient oxygen available – this is usually
during resting conditions once exercise has ceased.
• Only 1 mole of ATP can be recycled through
1 mole of PCr.
REMEMBER!
Don’t forget that for very high intense activities lasting less
than 3 seconds, such as a maximum weight lift, energy will
be provided solely through the breakdown of ATP.
Key terms
Sarcoplasm:
fluid that surrounds the nucleus of a muscle cell,
that is the site for both anaerobic energy pathways
Creatine kinase:
the enzyme used to release energy from
phosphocreatine
Endothermic reaction:
a chemical reaction that consumes energy
Coupled reaction:
a reaction where the product of one reaction is used
in a linked (second) reaction. the ATP-PC system is an
example of a coupled reaction
Fig.1.20 Muscle phosphagen depletion during a 100m sprint
Note that ATP levels remain high at the start of the race due to
the action of PCr providing energy to maintain levels. However,
after pproximately ten seconds, stores of phosphocreatine
have become depleted and ATP levels fall rapidly.
The lactic acid (lactate
anaerobic) system
Most activities last longer than the 10 second
threshold of the ATP-PC system. If strenuous
exercise is required to continue, ATP must be
resynthesised from another fuel source. In fact,
the body switches to glycogen (our stored form
of carbohydrate) to fuel the working muscles once
phosphocreatine stores have been depleted. The
glycogen which is stored in the liver and muscles
must first be converted into glucose-6-phosphate
before it is broken down to pyruvate by the enzyme
phosphofructokinase (PFK) in a process known
as glycolysis. It is during glycolysis (which takes
place in the sarcoplasm of the muscle cell) that
energy is released to facilitate ATP resynthesis. In
fact a net gain of 2 moles of ATP are gained for every
mole of glycogen broken down. In the absence of
oxygen, pyruvate is converted into lactate (lactic
acid) by the enzyme lactate dehydrogenase (LDH).
REMEMBER!
1. The ATP-PC system is of particular use to athletes who
compete at high intensity for about 10 seconds such as
a 100m sprinter or a gymnast performing a vault
2. Creatine supplementation: Some athletes seek
to extend the threshold of the ATP-PC system by
ingesting creatine monohydrate. Side effects such
as abdominal cramps, bloating and dehydration have
been recorded.
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Anaerobic glycolysis
in sarcoplasm of
the muscle cell
Glycogen (C6H12O6)
PFK
Glucose-6-phosphate
Pyruvic acid
Insufficient O2
LACTIC ACID
(2C3H6O3)
2ATP
LDH
energy systems
21
• During aerobic activities such as a 10,000m
run the lactic acid system can be called upon to
produce an extra burst of energy during the race or
indeed at the end of the race during a sprint finish.
Drawbacks of this system to
the athlete
• The most obvious drawback of this system is
the accumulation of lactic acid which can make
glycolytic enzymes acidic. This causes them to
lose their catalytic ability, inhibiting energy
production through glycolysis. The intensity of
the exercise must be reduced or in the worst case
scenario stopped so that the body can remove the
lactic acid that has accumulated.
• Only a small amount of energy (approximately 5%)
locked inside our glycogen molecule can be released
in the absence of oxygen.The remaining 95% can
only be released in the presence of oxygen.
C6
H12
O6
2(C3
H6
O3
) + ENERGY
(glucose) (lactic acid)
ENERGY + 2ADP + 2Pi 2ATP
Advantages of this system to
the athlete
• Because there are few chemical reactions,
ATP can be resynthesised relatively quickly for
activities or bouts of exercise that last between 10
seconds and 3 minutes.
• It is an anaerobic process and so does not need to
wait for the 3 minutes or so for sufficient oxygen
to be present.
• Any lactic acid that has accumulated can be
converted back into liver glycogen or indeed be
used as a metabolic fuel by reconversion into
pyruvate and entry into the aerobic system.
Site of reaction Fuel used Active enzyme Molecules of ATP produced
ATP splitting
ATP-PC system
Task 1.11
During a 100m sprint ATP will initially split to enable the athlete to drive away from the starting blocks.
PCr is then broken down to maintain a constant supply of energy for the remainder of the race.
Complete the table below with the required information.
Fig.1.21 A summary of the lactic acid system
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Percentage of VO2max
Bloodlactate(mmol/litre)
Lactate
threshold
shift
Lactate level
Untrained
performer
Trained
performer
50% 85%
applied physiology to optimise performance
22
The onset of blood lactate accumulation
describes the point at which lactic acid starts to
accumulate in the muscles. During normal resting
conditions the amount of lactic acid circulating in
the blood is between 1 to 2 millimoles/litre. This
rises dramatically during intense exercise. Quite
simply, the more intense the exercise the greater the
extent of lactic acid production. The OBLA is said
to occur when concentrations of lactic acid in the
blood reach 4millimoles/litre.
Just like VO2
max, OBLA occurs at different
intensities of exercise for different people and it is
expressed as a percentage of your VO2
max.
For the average untrained individual OBLA occurs
at around 55–60% of their VO2
max whilst trained
endurance performers can delay OBLA until they
have utilised 85–90% of their VO2
max.
Task 1.12
During a 400m hurdles race the ATP-PCr system
will be used during the first 10 seconds or so and
then the lactic acid system will provide the energy
for ATP resysnthesis for the remainder of the race.
Complete the table below with the required information.
Site of
reaction
Fuel
used
Active
enzyme
Molecules
of ATP
produced
Lactate
anaerobic
system
REMEMBER!
The lactic acid system is of particular use to athletes who
need to perform high intensity exercise for a period of
1–2 minutes. A 400m runner is an obvious example, as is
a squash player during a lengthy rally.
Fig 1.22 A comparison of the point of OBLA between trained
and untrained athletes when measured as a percentage of their
VO2
max
Key terms
Threshold:
the point where one energy system is exhausted and
another takes over as the predominant system, e.g. the
LA-O2
threshold represents the point where sufficient
oxygen becomes available to enable the aerobic system
to take over as the major energy provider
Glycogen:
the form of carbohydrate stored in the muscles and liver
Glycolysis:
the breakdown of glucose to pyruvic acid
REMEMBER!
You may have heard of the lactate threshold and
anaerobic threshold. Together with OBLA these describe
the same phenomenon.
Onset of blood lactate
accumulation (OBLA)
A large VO2
max sets the ceiling for endurance
performance and is an indication of the size of
our aerobic performance engine. However it is the
onset of blood lactate accumulation (OBLA) that
determines the actual percentage of that engine
power that can be utilised.
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energy systems
23
adapted to cope with higher levels of blood lactate
and increased the rate of its removal through effective
buffering.You will recall that untrained individuals
usually reach OBLA at about 55–60% of VO2
max.
With training this figure can increase to 70% or
even higher. Elite endurance athletes such as Lance
Armstrong have values approaching 90%. Whist
OBLA is a much greater product of training than
VO2
max it is still influenced by genetics.
A word on lactic acid
You will recall that lactic acid is produced when there
is insufficient oxygen available to sustain a given
exercise intensity.The pyruvic acid produced during
glycolysis is converted to lactic acid by the enzyme
lactate dehydrogenase. Once formed lactic acid quickly
dissociates into lactate and hydrogen ions (H+). It is
the presence of hydrogen ions that make the muscle
acidic and ultimately causes muscle fatigue.The acidic
environment slows down enzyme activity and ceases the
breakdown of further glycogen. High levels of acidity
can also irritate nerve endings which can cause some
degree of pain – the ‘heavy legs’ often associated with
lactic acid can thus be blamed on the hydrogen ions.
However lactic acid is not always the bad guy it
is made out to be. The heart, the liver, the kidneys
and inactive muscles are all locations where lactic
acid can be taken up from the blood and either
converted back into pyruvate and metabolised in the
mitochondria producing energy or converted back
to glycogen and glucose in the liver. The table below
summarises what happens to the lactic acid once it
has been removed from the muscle.
Lactate sampling and measuring OBLA
OBLA can only truly be measured in a sports science
laboratory. The test should be conducted using
a mode of exercise most suited to the performer,
usually a treadmill, bicycle ergometer, rowing
ergometer or swimming bench. Typically the test is
conducted in 4–6 stages. During the first stage the
exercise intensity is set at about 50% of VO2
max
and increases in intensity at the start of each of
the subsequent stages. Each stage generally lasts
about 5 minutes. At the end of each stage heart rate
recorded, oxygen consumption measured and blood
samples are taken by a small prick on the finger or
earlobe and the concentration of blood lactate is
analysed. The point at which blood lactate levels
rise to 4mmol/litre of blood usually signals OBLA.
The exercise intensity, oxygen consumption and
heart rate at this point is now recorded and used
to monitor progress and assess exercise intensity
during training.
OBLA and training
Improvements in endurance capacity can be observed
where lower lactate levels are recorded for any given
exercise intensity. This shows that the body has
Key terms
Onset of blood lactate accumulation
(OBLA):
the point at which lactic acid begins to accumulate in the
blood. Usually taken when concentrations of lactic acid
reach 4mmole/litre of blood
Millimole (mmole):
a unit used to measure the amount of a chemical
substance. It is equal to 1/1000 of a mole
Lactic acid from blood
Conversion into CO2
and H2
O Up to 65%
Conversion into glycogen Up to 20%
Conversion into protein Up to 10%
Conversion into glucose Up to 5%
Conversion into sweat and urine Up to 5%
Table 1.02 The fate of lactic acid
Apply it!
Lance Armstrong can tap into an exceptionally high
percentage of his VO2
max. His OBLA reportedly
occurs at 88.6% of his VO2
max.
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J7417
A2 PE For AQA
V499501_aw_020
190
180
170
160
150
140
130
120
110
12
10
8
6
4
2
0
30 33 40 45 50 55 60
Oxygen consumption
Heartrate
Lactateconcentration
Heart rate
Lactate concentration
Relationship of Oxygen Consumption to
Heart Rate Lactate Concentration
applied physiology to optimise performance
24
• The trained status of the working muscles:
If muscles are trained then they benefit from the
associated adaptive responses. These include
improved capacity for aerobic respiration due
to higher mitochondrial and capillary density,
improved use of fatty acids as a fuel (which do
not produce lactic acid!) and increased stores
of myoglobin.
Factors influencing the rate of
lactic acid accumulation
• Exercise intensity: the higher the exercise
intensity the greater the ATP demand which can
only be sustained using glycogen as a fuel. As fast
twitch fibres possess greater stores of glycogen
(and therefore lactate dehydrogenase) pyruvate is
soon converted to lactic acid.
• The respiratory exchange ratio (RER):
VCO2
expired/min
VO2
uptake/min
The closer the value is to 1.0 the more likely
the body is using glycogen as a fuel and the
greater the chance of lactic acid accumultation.
If the value is nearer 0.7 then fatty acids is the
likely fuel. This is also known as the respiratory
quotient.
• Muscle fibre type: Slow twitch fibres produce
less lactate at a given workload than fast twitch
fibres. As slow twitch muscle fibres possess
greater amounts of mitochondria, pyruvate will
tend to converted into Acetyl Co A and move into
the mitochondria with little lactate production.
• Rate of blood lactate removal: If the rate of
lactate removal equals the rate of production
then blood lactate concentrations should remain
constant. When the rate of lactate production
exceeds the rate of removal then blood lactate
will accumulate as we reach OBLA.
Task 1.13
Using the information from table 1.04 plot a
graph of blood lactate accumulation (mmol/litre on
y axis) against running speed (ms–
¹ on x axis).
1. On your graph show the point of OBLA. Give a
brief explanation as to why you have chosen this point
on the graph.
2. At what running speed did OBLA occur?
Blood lactate
(mmol/litre)
2.9 3.7 5.7 9.1
Running speed ms–
¹ 3.5 4.00 4.5 4.9
Task 1.14
The graph below provides data gained from an
OBLA test on a middle distance runner.
1. Use the graph to calculate OBLA of the runner
given she has a VO2
max of 61ml/kg/min.
2. If her HRmax is 182bpm at what percentage of
HRmax does OBLA occur?
Fig 1.23 The relationship of oxygen consumption
to heart rate and lactate concentration of a middledistance
runner during a maximal test to exhaustion
Apply it!
A cyclist during a time trial can use data from the
OBLA test to determine her racing heart rate by
calculating the percentage of HRmax that leads to
OBLA. If she had a HRmax of 182bpm and OBLA occurred
at a HR of 158bpm this equates to about 87 per cent of
HRmax. Her racing heart rate should be somewhere just
below this point.
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energy systems
25
Key terms
Buffering:
a process which helps in the removal of lactic acid and
maintains blood and muscle pH (acidity)
Adaptive responses:
the anatomical and physiological changes that occur to
the body as a consequence of training
Exam tips:
1. Although lactic acid and lactate are often used
interchangeably, they are not in fact the same thing.
2. The following equation can be used to calculate the
percentage of VO2
max used by a performer:
VO2
(amount of O2
used)
VO2
max (max potential)
Athlete Profile
Becky Wing is currently studying AS PE at Sixth Form College in Farnborough, Hampshire.
At the age of 16, Becky is already an Olympian. She was a member of the Great Britain
Gymnastics team in the Beijing Olympics finishing in 9th place in the team event. She is
currently preparing for the 2012 London Olympics.
Becky has access to three personal coaches at her Heathrow Gymnastics Club
and two National gymnastic coaches. She trains between 4 to 6 hours, 6 days
per week. Each session will consist of a half-hour warm up and up to 1
hour of conditioning work. The conditioning work mainly focuses on the
development of explosive strength and muscular endurance, the two
key components of fitness required by gymnasts. Her explosive
strength training which consists of plyometrics type activity will
help develop and improve the efficiency of her ATP-PC system whilst the muscular endurance
training will seek to enhance the removal of lactic acid extending the time that she can use the
lactate anaerobic system before fatigue sets in. This will of course be essential during a floor
routine which consists of approximately 90 seconds of very high intensity activity.
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26 ExamCafé
Refresh your memory
ExamCaféRelax, refresh, result!
Revision checklist
Make sure you know the following:
3 Energy is the capacity to perform work.
3 Energy is measured in calories (kcal) or joules (J). 1 calorie = 4.184 joules.
3 The food fuels: fats, carbohydrates and proteins are the major energy sources in
the body.
3 Food fuels however are only a secondary source of energy – the energy stored
within them must first be converted and stored as adenosine triphosphate (ATP)
before it can be accessed.
3 ATP is the energy currency of all cells and is the only direct source of energy in
the body.
3 When energy is required ATP is broken down by the enzyme ATPase to release
energy plus ADP (adenosine diphosphate) and an inorganic phosphate (Pi)
ATP ADP + Pi + Energy.
3 This reaction is exothermic which means that energy is released in the form of heat.
3 There is only sufficient ATP stored within the muscles to perform high intensity
exercise for 2 or 3 seconds.
3 Once ATP has been broken down to release energy it must be constantly recycled.
3 There are three energy systems that provide the energy for ATP resynthesis.
3 The source of energy for ATP resynthesis is dependent upon primarily the intensity
and then the duration of the activity.
3 During low intensity exercise of longer duration the aerobic (oxidative) energy
system is used for ATP resynthesis.
3 During medium–high intensity exercise the lactic acid system is used for
ATP resynthesis.
3 During short periods of maximum exercise intensity the ATP-PC (alactic) energy
system is used for ATP resynthesis.
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ExamCafé 27
Aerobic energy systems
3 The aerobic system uses a combination of fats and carbohydrates to provide the
energy for ATP resynthesis.
3 The aerobic system is the most efficient energy system yielding 18 times more
energy than anaerobic processes.
3 The site for aerobic respiration are the mitochondria which are the powerhouses of
the muscle cells.
3 The Krebs cycle takes place in the matrix of the mitochondria and produces carbon
dioxide and sufficient energy to recycle 2 moles of ATP.
3 The electron transport system is the final stage of the aerobic system which
produces water and enough energy to resynthesise 34 moles of ATP.
3 Enzymes used in the aerobic system include phosphofructokinase (PFK), glycogen
phophorylase (GP) and lipase.
3 As the duration of the exercise period increases fatty acids become the preferred
fuel as more energy can be elicited from one mole of fatty acids than from one
mole of glycogen.
3 The complete breakdown of one mole of glycogen can be summarised as follows:
C6
H12
O6
+6O2
6CO2
+ 6H2
O + Energy
Energy + 38ADP + 38Pi 38ATP
3 Recovery is concerned with returning the body to its pre-exercise state.
3 Recovery can only occur via the aerobic system and only then when there is
sufficient oxygen available.
3 The oxygen deficit is the volume of oxygen required to complete an activity entirely
aerobically.
3 Excess post-exercise oxygen consumption (EPOC) is the volume of oxygen
consumed during recovery above that which normally would have been
consumed at rest during the same period of time.
3 There are two stages to EPOC: the fast and slow stages.
3 The fast stage of EPOC occurs rapidly, taking just 2–3 minutes.The oxygen consumed
during this stage is used to replenish ATP and PC stores and to re-saturate myoglobin.
3 The slow stage of EPOC takes up to 1 hour.The oxygen consumed during this stage
is used to remove lactic acid and provide the energy to maintain elevated heart
and respiratory rates.
3 A low VO2
max score can limit performance in endurance activities.
3 Factors that can limit VO2
max include: genetics, physiological make-up, lifestyle
choices, age, sex, and the volume of training undertaken.
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Anaerobic energy systems
3 The ATP-PC system is the first of the anaerobic energy systems and used in those
activities that are of the highest intensity but short in duration, lasting between 3 and
10 seconds – such as a 100m sprint.
3 The fuel for resynthesis in the ATP-PC system is phosphocreatine, a high energy
compound found in all muscle cells.
3 Enzymes used in the ATP-PC system include creatine kinase which breaks down PC.
3 The ATP-PC system involves a coupled reaction which occurs when the product of
one reaction is used in a second reaction.
3 The ATP-PC system can be summarised as follows:
PC Pi + C + Energy; Energy + ADP + Pi ATP
3 The main drawback of the ATP-PC system is that there is only a limited supply of PC
in the muscle cell which is exhausted after approximately 10 seconds.
3 The lactate anaerobic or lactic acid system is predominant in activities of moderate
to high intensity that are of 1–3 minutes’ duration – such as a 400m run.
3 The lactate anaerobic system involves the process of glycolysis, which relates to the
breakdown of glycogen and glucose.
3 Under the lactate anaerobic system, energy resulting from the breakdown of
glycogen into pyruvate is sufficient to recycle 2 moles of ATP.
3 Enzymes involved in glycolysis include phosphofructokinase (PFK) and glycogen
phosphorylase (GP).
3 In the absence of oxygen pyruvate is converted into lactic acid by the enzyme
lactate dehydrogenase.
3 Any lactic acid produced during exercise can be converted back into liver glycogen
or used as a metabolic fuel by reconversion into pyruvate and entry into the aerobic
system.
3 The lactate anaerobic system can be summarised as follows:
C6
H12
O6
2C3
H6
O3
+ Energy; Energy + 2ADP + 2Pi 2ATP
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3 Drawbacks of the lactate anaerobic system include the fatiguing effect of lactic
acid on the muscles, and the fact that only a tiny amount (5%) of the energy stored
within the glucose molecule can be accessed to provide energy for ATP resynthesis.
3 The onset of blood lactate accumulation (OBLA) is the point at which lactic acid
begins to accumulate in the blood.
3 OBLA is usually said to have occurred when concentrations of lactic acid reach
4mmol/litre of blood.
3 OBLA can be expressed as a percentage of VO2
max.Trained performers can
achieve a higher percentage of their VO2
max than the untrained.Training
therefore delays OBLA.
3 The rate of lactate accumulation is dependent upon exercise intensity,muscle fibre
type,the trained status of the working muscles and the rate of blood lactate removal.
3 Buffering is a process which helps in the removal of lactic acid and maintains blood
and muscle pH at acceptable levels.
3 The removal of lactic acid occurs in a number of different ways: up to 65% is
converted into carbon dioxide and water; up to 20% is converted back into muscle
and liver glycogen; up to 10% is converted into protein, up to 5% is converted into
blood glucose; up to 5% is removed as sweat and urine.
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30 ExamCafé
1. Write out an equation which
summarises each of the three energy
systems.
2. Explain the specialist role of the
mitochondria in the production
of energy.
3. Draw a diagrammatic representation
of each of the three energy systems.
4. Compare the three energy pathways
with regard to their relative efficiency.
5. Explain the energy continuum in
relation to a games player of your
choice. Use specific examples from
the game when each energy system is
likely to be in use.
6. Explain what happens when a
marathon runner ‘hits the wall’.
7. What nutritional advice would you
give a marathon runner preparing for
a major competition in the coming
week?
8. Construct a food fuel graph which
illustrates the predominant food fuel
against time during a triathlon.
9. Why might performers take creatine
supplements? What type of performer
is likely to benefit from creatine
supplementation?
10. Outline some methods of training you
would use to develop and improve
your ATP-PC system. For one of these
methods give an example of a
training session.
11. Define VO2
max.
12. Suggest typical VO2
max values for the
following:
a) a healthy male ‘A’ level PE student
b) a centre in netball
c) an Olympic rower.
13. The multi-stage fitness test or ‘bleep
test is often used to determine the
VO2
max of an athlete. Briefly outline
this test and give reasons why this may
not be the most accurate test to use.
14. Identify and explain the procedures of
a more valid test that may be used.
15. Outline the factors that could limit
VO2
max.
16. Suggest a method to improve VO2
max.
17. Explain why the VO2
max of women is
typically 15–20 per cent lower than that
of men from the same activity group.
18. Define the following terms:
• recovery
• oxygen deficit
• EPOC
19. How long does it take the fast
component of EPOC to recover?
20. How is lactic acid removed from the
muscle following a 400m run? What
organs and tissues are involved in the
removal of lactate?
21. Explain the terms ‘active recovery’ and
‘rest recovery’. How do these different
types of recovery influence the speed
of lactate removal?
Revise as you go
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31ExamCafé
22. Explain the replenishment of muscle
glycogen stores with reference to:
• the type of exercise performed
• the post-event meal.
23. Outline the recovery patterns for the
following performers:
• a gymnast performing a vault
• an ‘iron-man’ triathlete
• a 200m butterfly swimmer.
24. Swimmers are often required to
compete in several events during a
swimming gala.What advice would
you give a swimmer concerning
recovery between events?
25. Briefly explain why EPOC is often larger
than the oxygen deficit.
26. How can knowledge of the recovery
process be of use to the coach and
athlete when designing training
programmes?
27. Explain what you understand by the
term ‘OBLA’.
28. OBLA and lactate threshold are often
used interchangeably. How is the
lactate threshold related to VO2
max?
29. At what point does OBLA typically
occur? What might cause an athlete
to reach OBLA?
30. Andrew Johns represents Great Britain
in Triathlon. Explain how knowledge of
blood lactate levels during a triathlon
might assist his performance.
31. Briefly outline the factors that affect
the rate of lactate accumulation.
32. Explain what you understand by the
term ‘buffering’. How does the body
buffer lactic acid?
33. What happens to lactic acid once it
has been produced in the body?
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