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Energy concepts
Before looking at energy definitions, it is useful to understand where energy begins and ends. There are many forms of energy but you are required to understand just three forms. These are better learned if you follow the original source of all energy: light from the sun. Plants convert light energy into stored chemical energy , which humans then obtain by their consumption of those plants or of the animals that eat plants. People store this energy as carbohydrates, fats or proteins – chemical compounds composed of carbon, hydrogen and oxygen bonds storing energy. We do not directly use energy from these chemical stores for muscular work but further store this chemical energy in the form of a high energy compound called adenosine triphosphate (ATP) within our muscles. Energy stored within the compound ATP is termed potential energy and it is readily available as an energy source for the muscles to contract. The energy used to make the muscles contract is termed kinetic energy. Fig 16.1 shows the conversion of energy from light to chemical to potential and finally to kinetic energy in the form of muscular contractions.
By the end of this chapter you should have knowledge and understanding of:
**- how to define energy, work and power
- the role of ATP; the breakdown and re-synthesis of ATP; coupled reactions and**
exothermic and endothermic reactions
**- the three energy systems: ATP/PC; alactic; the lactic acid and aerobic system
- the contribution of each energy system in relation to the duration/intensity of exercise
- the predominant energy system used related to type of exercise
- the inter-changing between thresholds during an activity, for example the onset of**
blood lactate accumulation (OBLA), and the effect of level of fitness, availability of
oxygen and food fuels, and enzyme control on energy system used
- how the body returns to its pre-exercise state: the oxygen debt/excess post-exercise
oxygen consumption (EPOC); the alactacid and lactacid debt components; replenishment
of myoglobin stores and fuel stores and the removal of carbon dioxide
- the implications of the recovery process for planning physical activity sessions.
LEARNING OBJECTIVES
CHAPTER 16:
Energy
KEY TERMS
Chemical energy Energy stored within the bonds of chemical compounds (within molecules).
Adenosine triphosphate (ATP) Chemical energy stored as a high energy compound in the body. It is the only immediately usable source of energy in the human body.
Potential energy ‘Stored’ energy which is ready to be used when required.
Kinetic energy Energy in the form of muscle contraction/joint movement.
energy
Energy Energy is the ability to perform work or put mass into motion. When applied more directly, energy refers to the ability of the muscles to contract (kinetic energy) and apply force that may limit or increase performance in physical activity.
Energy is usually measured in joules (J), which is the unit to describe the force 1 Newton (equivalent to 1 kilogram) acting through a distance of 1 metre. Energy is also measured in calories, where 1 calorie is equal to 4.18 joules.
Work Work is done when a force is applied to a body to move it over a certain distance. It is expressed as follows:
Work = force (N) x distance moved (m)
The units of measurement for work are joules (j).
Sun (solar energy)
Plants (chemical energy)
ATP = energy
(Kinetic energy)
(stored chemical/potential energy)
Movement (^) (sweating)
Heat energy
CHOs
Carbohydrates, fats and proteins
ATP
Fig 16.1 Energy conversion from light to kinetic energy
‘The body’s maximum efficiency of converting food into motion is about 27 per cent. Hence the body is actually not very efficient at converting chemical energy into kinetic energy.’
1 What do you think happens to the remaining percentage of energy? 2 Discuss the statement above in relation to the efficiency of the human body.
stretch and challenge
KEY TERM
Force A pull or push that alters, or tends to alter, the state of motion of a body. It is measured in Newtons (N).
task 1
Calculate the work to move a sprinter
weighing 85 kg a distance of 4 metres.
APPLY IT!
Remember that 1 Joule = 1 Newton (1 Newton acting through a distance of 1 metre). Hence, to move a 100-metre sprinter weighing 75 kg a distance of 1 metre requires a force of 750 N, and therefore to move the sprinter 2 metres requires a force of 1500 N.
energy
an exothermic reaction as it releases energy and in doing so it leaves behind a compound termed adenosine diphosphate (ADP). Although this is more complex, it is easier to think of ADP as having lost its high energy bond between the last two phosphates.
Fig 16.2 highlights that the major role of ATP is to act as a potential energy store to supply the energy for muscle contractions (kinetic energy). But why is it so important? ATP is the only usable source of energy that the body/muscles can utilise for work. Hence no ATP means no energy for work and thus muscle fatigue.
ATP is a simple compound which can be quickly broken down and is stored exactly where it is needed within the muscles. However, there is a major problem in that the body only has limited stores of ATP – enough to supply energy for approximately 2−3 seconds of muscular work. So, how can athletes exercise for long periods if the only usable source of energy runs out after 2 −3 seconds?
KEY TERMS
Compound A mixture of elements.
enzymes Protein molecules that act as catalysts for the body’s chemical reactions. The enzyme name typically ends with the suffix – ase.
ATPase The enzyme that helps break down ATP to release energy.
exothermic A chemical reaction that releases energy as it progresses.
ATP resynthesis Since ATP is the only usable source of energy for work, it is clear that the body needs to rebuild ATP as quickly as it uses it. This is achieved by a process called ATP resynthesis, by which the breakdown of ATP into ADP becomes a reversible reaction.
The simplest way to understand how ATP resynthesis works is to think of what was removed from ATP to form ADP. You will remember that energy from the last two P bonds was removed and used for muscular work. Therefore, to re-synthesise ADP back into ATP, additional energy is needed to rebuild the bond between the two phosphates. This reversible reaction requires energy and is therefore termed an endothermic reaction.
KEY TERMS
endothermic A chemical reaction that requires energy to be added for it to progress.
Coupled reactions When the products from one reaction, such as energy, are then used in another reaction.
There is, however, one major problem: where does the energy to resynthesise ADP back into ATP come from? The body has three energy systems: ATP/PC, lactic acid and aerobic, which have the same function. Via coupled reactions , these supply energy to re-synthesise ADP back into ATP. As you will see, these three energy systems do not work in isolation but work together to provide a constant supply of energy to resynthesise ATP. You will also see that the relative contribution of energy supplied from each energy system is primarily dependent upon the duration and intensity of exercise.
exerCise And sPorT Physiology
The ATP/PC (Alactic) system
The ATP/PC energy system provides energy, via coupled reactions, to resynthesise ADP back into ATP. PC (phospho-creatine) is another high-energy phosphate compound which stores potential energy. When ATP levels fall and ADP levels increase, this stimulates the release of the enzyme creatine kinase, which breaks down the PC bond releasing energy (exothermic reaction). This energy cannot be used for muscular work but is coupled to the resynthesis of ADP back into ATP. Fig 16.3 below shows this coupled reaction, where the energy released from PC is used to resynthesise ADP back into ATP in an endothermic reaction.
Although the ATP/PC system can work aerobically, it does not require oxygen so is termed anaerobic and takes place in the sarcoplasm of muscle cells. As a simple compound located exactly where it is required, PC is quickly broken down. However, with limited stores and with just one PC resynthesising only one ATP, it can only supply energy to resynthesise ATP for 3 to 10 seconds during an all-out maximal sprint.
Exam tip
When answering energy system questions, always ask ‘where has the energy come from?’ If it is not ATP then it cannot be used for muscular work; it is more likely to be energy that has been released to resynthesise ADP back into ATP as part of a coupled reaction.
KEY TERMS
Anaerobic A reaction that can occur without the presence of oxygen.
sarcoplasm Fluid-like gelatine that fills the spaces within the muscle cells and is a store of glycogen, fat, proteins, enzymes and myoglobin.
Time (s)
Exhaustion
100 80 60
40 20 (^0 0 )
PC ATP
4 6 8 10 12 14
% of resting value
Fig 16.4 Breakdown of PC coupled to ATP resynthesis during sprinting (Source: J. Wilmore and D. Costill, Physiology of Sport and Exercise, 2nd edition, 1998)
APPLY IT! The ATP/PC system is the predominant energy system used when requiring high intensity, very short duration moments or events, for example the 100-metre sprint, long/triple jump and team games requiring explosive jumping to head, catch or dive for a ball.
(PC) = C ENERGY C + + (^) ENERGY + ADP ATP
Creatine Kinase
P P
Fig 16.3 Break down of PC coupled to the resynthesis of ATP.
Fig 16.4 is a graphical representation of how PC is broken down in order to maintain the body’s supply of ATP during a sprint. There are no fatiguing by-products, creatine and Pi remain in the muscle cell until, during recovery, they are resynthesised back into PC via energy from the aerobic system.
exerCise And sPorT Physiology
During glycolysis, the enzyme phosphofructokinase (PFK) initiates the partial breakdown of glucose into pyruvic acid (pyruvate C 3 H 4 O 3 ), but in the absence of sufficient oxygen, pyruvic acid is further broken down into lactic acid by the enzyme lactate dehydrogenase (LDH). Fig 16.5 summarises how the breakdown of one mole of glucose is coupled to the resynthesis of two moles of ATP.
Although more complex and therefore slower than the reactions of the ATP/PC system, the LA system is still a relatively quick process as it is not dependent upon oxygen. Furthermore, glycogen is readily available as an energy fuel in the muscles.
The LA system provides energy to resynthesise ATP during the first 2–3 minutes of high- intensity short-duration anaerobic activity. If exercise is flat out to exhaustion, the LA system may only last for up to 30 seconds, but if the intensity is lowered then duration may prolong for up to a few minutes of anaerobic activity. The main limitation of the LA system is due to the onset of blood lactate accumulation (OBLA). As lactic acid (C 3 H 6 O 3 ) accumulates it decreases the pH (higher acidity) within the muscle cells, which inhibits the enzymes involved in glycolysis and thus prevents the breakdown of glucose and induces muscle fatigue.
Muscle/liver glycogen
M U S C L E
S A R C O P L A S M
Glycogen phosphorylase
PFK
LDH
Anaerobic ENERGY glycolysis
Pyruvic acid
2 ATP
Lactic acid
Glucose
Fig 16.5 Anaerobic glycolysis – the breakdown of glycogen into glucose and ATP
remember The energy released from glycogen/glucose via anaerobic glycolysis is not used for muscular work but to resynthesise ADP back into ATP in a coupled reaction.
APPLY IT!
The LA system is the predominant energy system for the 400-metre sprint and for midfield team games players when they have a high number of repeated high-intensity sprints without any time to recover.
KEY TERM
lactate/lactic acid Anaerobic glycolysis produces lactic acid (C 3 H 6 O 3 ), but it is quickly converted into a substrate salt called lactate which is easier to disperse via the blood stream. Although different compounds, the terms ‘lactate’ and ‘lactic acid’ are often used interchangeably.
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Training adaptations Repeated bouts of anaerobic training which overload the LA system increase the body’s tolerance to lactic acid and its buffering capacity against high levels of lactic acid. Similarly, they increase the body’s stores of glycogen. This has the effect of delaying the OBLA and prolonging the lactic acid system threshold by delaying fatigue. This allows athletes to work at higher intensities for longer periods, which is invaluable in events such as the 400-metre sprint/hurdles and 50−100m events in swimming. It also allows team games players to carry out a higher percentage of repeated sprints before muscle fatigue occurs.
Table 3 Advantages and disadvantages of the lA system
Advantages disadvantages
- Large glycogen store in muscle/liver is readily available as a potential energy source
- Resynthesises two molecules of ATP – more than the PC system
- Requires fewer reactions than the aerobic system so provides a quicker supply of energy
- Glycogen phosphorylase and PFK enzyme activation due to a decrease in PC
- Provides energy for high-intensity exercise lasting between 10 and 180 seconds
- Can work aerobically and anaerobically
- Not as quick as ATP/PC system
- Produces lactic acid, which is a fatiguing by-product
- Reduces pH (increased acidity) which inhibits enzyme action
- Stimulates pain receptors
- Net effect is muscle fatigue and pain
remember
Don’t be misled by questions which ask you to explain when and why the energy systems are used. Simply answer which of the advantages/ disadvantages are applied to when or why as highlighted in Tasks 3, 4 and 5.
task 4
For each of the advantages and
disadvantages listed in Table 3, identify
whether they can explain when or why the
lA system will be used.
The aerobic energy system The aerobic or ‘oxidative’ system breaks down glycogen, glucose and fats to provide energy, via coupled reactions, which is used to resynthesise ADP back into ATP. Unlike the LA system, the aerobic system uses oxygen to completely break down one mole of glucose into H 2 O and CO 2 in three complex stages:
- Stage 1: Aerobic glycolysis
- Stage 2: Kreb’s cycle
- Stage 3: Electron transport chain (ETC)
Stage 1: Aerobic glycolysis Aerobic glycolysis is the same process as anaerobic glycolysis except that the presence of oxygen inhibits the accumulation of lactic acid by diverting pyruvic acid further into the aerobic system. Pyruvic acid combines with coenzyme A to form Acetyl CoA. This is a complex series of reactions which is easier learned diagrammatically in stages using Fig 16.6 and translating (+) into ‘combines with’ and (=) into ‘to form’.
APPLY IT! The ATP/PC and LA systems are the predominant energy systems used during the first few minutes of high-intensity low-duration exercise. However, they are unable to provide all the energy required beyond this time and they are both reliant on the aerobic energy system to help them recover during and after exercise.
energy
Stage 2: Kreb’s cycle The Acetyl CoA from Stage 1 combines with oxaloacetic acid to form citric acid. This is then further broken down in a series of complex reactions within the matrix of mitochondria , where four events take place:
1 CO 2 is produced and removed via the lungs 2 hydrogen atoms are removed (oxidation) 3 energy is produced to resynthesise two molecules of ATP 4 oxaloacetic acid is regenerated.
Follow the four events above in Stage 2 of Figure 16.6b to identify how the Kreb’s cycle can continue to break down the Acetlyl CoA produced from aerobic glycolysis in Stage 1.
e- + ETC
H + ETC
=
= H 20
Mitochondria cristae folds
Mitochondria matrix
C R I S T A E
of
M I T O C H O N D R I A
=
NAD & FAD
NADH & FADH
H
H+
e-
e-
H+
- Energy for 34 ATP
Fig 16.6 c) Electron transport chain (ETC)
KEY TERMS
Matrix Intracellular fluid within the mitochondria where oxidation takes place.
Mitochondria Small sub-unit (membrane) sites of a muscle cell where aerobic respiration takes place.
Exam tip
You should never write in an answer that aerobic glycolysis is the same as anaerobic glycolysis. You must write out the process again but add the changes that occur in the presence of oxygen.
(c)
exerCise And sPorT Physiology
Stage 3: Electron transport
chain (ETC) In Stage 3 the hydrogen atoms combine with the coenzymes NAD and FAD to form NADH and FADH, and are carried down the electron transport chain (ETC) where hydrogen is split into H+^ and e-. This takes place within the cristae folds of the mitochondria, where three important events take place:
1 the hydrogen electron (e-) splits from the hydrogen atom and passes down the ETC 2 this provides sufficient energy to resynthesise 34 ATP 3 the hydrogen ion (H +) combines with oxygen to form H 2 O (water).
The total energy produced via the aerobic system is therefore 38 ATP:
- 2 ATP from aerobic glycolysis
- 2 ATP from the Kreb’s cycle
- 34 ATP from the ETC.
This is summarised by an equation that represents aerobic respiration:
KEY TERM
Cristae
Internal membrane/compartments/fold-like structures within mitochondria.
Follow the three events above in Stage 3 of Figure 16.6c to identify how the ETC completes the full breakdown of glucose by converting hydrogen into H 2 O and providing energy to resynthesise 34 ATP.
C 6 H 12 O 6 + 6O 2
= (carbon dioxide) + (water) + energy
(glucose) + (oxygen)
= 6CO 2 + 6H 2 O + energy (for the resynthesis of 38 ATP)
Table 4 The advantages and disadvantages of the aerobic system
Advantages disadvantages
- Large potential glycogen and FFA stores available as an efficient energy fuel - Slower rate of ATP resynthesis compared with LA system due to points 2−4 below
- Efficient ATP resynthesis when good O 2 supply guarantees breakdown of FFAs - Requires more O 2 supply (15 per cent more for FFAs)
- Large ATP resynthesis: 38 ATP from one molecule of glucose compared to 2 ATP from LA system and 1 from ATP/PC - More complex series of reactions
- Provides energy for low/moderate-intensity high-duration exercise (3 minutes to 1 hour) - Cannot resynthesise ATP at the start of exercise due to initial delay of O 2 from the cardiovascular system
- No fatiguing by-products; CO 2 and H 2 O easily removed - Limited energy for ATP during high-intensity short-duration work
Although seemingly complex, this equation is simply showing that glucose (C 6 H 12 O 6 ) is completely broken down by oxygen (6O 2 ) in the aerobic system into carbon dioxide (6CO 2 ) and water (6H 2 O) to release sufficient energy to resynthesise 38 ATP.
Exam tip
If the equation for aerobic respiration is too daunting, just remember to describe the process without the complex equation.
exerCise And sPorT Physiology
Predominant E system/s
0.1 s 1/3 s 10 s 2/3 min Time (sec/min)
LA System
- Enzyme activation levels 4. Food / Fuel available
- Energy System THRESHOLD
- 0 2 transport / supply
- Exercise Intensity & Duration
- Fitness level
Aerobic System
Anaerobic work
Overall performance / work rate
Aerobic work
Energy System thresholds
ATP ATP-PC
45+ min
Capacity of energy system %
100
0 10 20 2 min Time
Anaerobic Glycolysis (LA) System Aerobic Energy System
ATP-PC
5 min +
Fig 16.7 Energy system interaction linked to exercise duration
Fig 16.8 Factors affecting the energy system/s utilised
energy
Factors affecting the
energy systems used
Intensity and duration of exercise Figs 16.7 and 16.8 show that it is a combination of both exercise intensity and duration that determines the predominant energy system/s being used. When the exercise intensity is anaerobic (high intensity, short duration) then the ATP/PC and LA systems will be the predominant systems, whereas if the intensity is aerobic (medium/low intensity, long duration) the aerobic system will be predominant.
When exercise intensity reaches a point that the aerobic energy system cannot supply energy quick enough, it has to use the lactic acid system to continue to provide energy for the resynthesis of ATP. You will remember that the LA system produces lactic acid as a by-product. During higher intensity exercise, lactate production will start to accumulate above resting levels and this is termed the ‘lactate threshold’. When blood lactate levels reach 4 mmol/L, the exercise
intensity is referred to as ‘the onset of blood lactate accumulation’ (OBLA; see Fig 16.9). This 4 mmol/L is an arbitrary standard value for when OBLA is reached and in essence represents a point where the production of lactate exceeds the speed of its removal. OBLA will continue to increase if this exercise intensity is maintained or increased and will eventually cause muscle fatigue. Fig 16.10 shows that after training the intensity level for lactate threshold is increased and this subsequently delays the point that OBLA is reached and therefore increases the potential duration/threshold of the lactic acid energy system.
Blood lactate (mmol/L)
2
4
6
8
10
12
14
1.0 1. Exercise velocity (m/s)
1.4 1.6 1.8 2.0 2.
LT OBLA
Fig 16.9 The link between lactate threshold and OBLA
Blood lactate (mmol/L)
0
2
0
4
6
8
10
12
14
5 Treadmill speed (km/h)
10 15 20 25
Pretraining Post-training
LT
LT
Fig 16.10 The effect of training on the lactate threshold
APPLY IT!
- A sprint athlete may have the potential to sprint at a higher/the same intensity for a longer duration before OBLA induces muscle fatigue.
- An endurance athlete can exercise just below the lactate threshold/OBLA at a higher pre-training intensity without inducing muscle fatigue.
energy
intensity of about 85 per cent of their maximal, whereas a 400m sprinter may be at 65 per cent and the 800m runner below this again. This shows that although all these events are predominantly LA/anaerobic (high intensity, short duration) events, by changing the intensity the duration before the threshold of the LA system is reached can be altered. Similarly, during team games a performer will be continually switching between all three energy systems and will not be limited to the times in Table 6, which assume that exercise continues to use the same energy system until it is completely exhausted. The ATP/PC system in particular demonstrates this as Table 6 suggests it can last for up to 10 seconds of flat-out sprint activity. However, during a team game the aerobic system is continually resynthesising ATP/ PC during periods of recovery. This allows it to repeatedly be used intermittently during the game as the predominant system when explosive/short sprint-type movements are performed.
Fuel availability As long as 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 intensity starts too high, then PC stores will quickly deplete and continued high-intensity explosive activity cannot be sustained. PC stores can be conserved by pacing and by resynthesising PC stores during periods of recovery using spare energy from the aerobic system.
Glycogen is the major fuel for the first 20 minutes of exercise, initially because oxygen supplies are limited as it takes 2–3 minutes for the cardiovascular systems to supply sufficient oxygen. Similarly, glycogen is readily available in the muscles, requires less oxygen and therefore is quicker/easier to break down than free fatty acids (FFAs), to allow a higher aerobic intensity of activity. After about 20−45 minutes there is greater breakdown of fats alongside glycogen as the energy fuel. Although FFAs are a more efficient fuel than glycogen, they require about 15 per cent more oxygen to break them down and will result in the athlete having to work at lower intensities. The greater the liver/muscle glycogen stores, then the longer the performer can work aerobically at a higher intensity.
When glycogen stores become almost fully depleted, after about two hours, FFAs have to be used for aerobic energy production, and unless exercise intensity is reduced it can bring on the sudden onset of fatigue which many athletes refer to as ‘hitting the wall’. Similarly, once the onset of blood lactate accumulation (OBLA) is reached the body has insufficient oxygen available to burn FFAs and therefore has to break down glycogen ‘anaerobically’ to continue resynthesising ATP. Generally it can be said that high-intensity short-duration activity will break down glycogen as the energy fuel, for example a team game player will use glycogen when sprinting. Low-intensity long-duration aerobic activity will break down FFAs and glycogen as energy fuel, for example in a team game a player will use FFAs to last the full duration of the game.
Exam tip
A common mistake is to think a threshold is when an energy system ‘stops’ providing energy to resynthesise ATP. If you do use the term ‘stop’, it is best to word your response as ‘stops being the predominant energy system’.
Oxygen availability As long as there is a sufficient supply of oxygen, the aerobic system can provide the energy to resynthesise ATP. If oxygen supply falls below that demanded for the exercise, then the aerobic system threshold is met and the LA system will begin to breakdown glucose anaerobically to resynthesise ATP. The availability of oxygen is dependent upon the efficiency of the respiratory and cardiovascular systems to supply oxygen to the working muscles and ultimately determines the efficiency and therefore threshold of the aerobic system to resynthesise ATP. Oxygen supply also affects which food fuels can be broken down to resynthesise ATP.
exerCise And sPorT Physiology
Enzyme activation level You will remember that enzymes are catalysts that activate the many reactions that help break down PC, glycogen, glucose and FFAs to provide the energy to resynthesise ATP. Hence, without enzymes there would be no reactions and therefore no energy for ATP resynthesis. Table 7 summarises the factors that activate the enzymes for each of the energy systems.
Fitness level Generally, the more aerobically fit the performer, the more efficient their respiratory and cardiovascular systems are to take in, transport and use oxygen to break down glycogen and FFAs aerobically to resynthesise ATP. Aerobic athletes have also shown that they can start to use FFAs earlier during sub- maximal exercise and therefore conserve glycogen stores. The net 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 approx 50/56 per cent of their VO 2 max , whereas an aerobic-trained athlete wouldn’t reach OBLA until about 85/90 per cent of their VO 2 max.
In the same way, an anaerobic-trained athlete will increase their ATP/PC, glycogen stores, anaerobic enzymes and tolerance to lactic acid, which would increase the threshold of both the ATP/PC and LA systems.
Table 7 Factors affecting enzyme activation for the energy systems
Activating factor releases controlling enzyme/s Activating energy system
Increase in ADP; decrease in ATP Creatine Kinase
PC
Decrease in PC PFK LA system
Increase in adrenalin; decrease in insulin PFK Aerobic system
KEY TERM
Vo 2 max
Maximum oxygen consumption attainable during maximal work.
APPLY IT! A marathon runner uses glycogen/glucose as the primary energy fuel for the first 20− 30 minutes of exercise. After about 45 minutes, glycogen stores begin to deplete and there is a greater mix of glycogen and FFA fuels as exercise continues. FFAs can only be broken down aerobically and require 15 per cent more oxygen. This places greater demands on the cardiovascular system to deliver sufficient oxygen quickly enough to sustain exercise intensity. As glycogen depletion increases, more FFAs have to be used. If the exercise intensity is to be maintained there will be insufficient oxygen supply to break down FFAs and the LA system would be used to break down the remaining glycogen stores. As a consequence this will bring about the onset of blood lactate accumulation (OBLA) and thus eventually muscle fatigue. The athlete would have the choice to reduce their exercise intensity to match their body’s capacity to supply oxygen and continue using the aerobic system to break down the FFAs. After about two hours, glycogen stores are almost fully depleted and the runner will most likely ‘hit the wall’ and has two options: slow down to a pace where the available oxygen supply can break down FFAs aerobically, or risk muscle fatigue and failure to complete the race. This stresses the importance of conserving, maintaining or increasing the body’s most important energy fuel – glycogen.
On pages 488–491 we will be looking in more detail at the use of nutritional ergogenic aids before, during and after exercise in an attempt to overcome this problem of glycogen depletion.
exerCise And sPorT Physiology
The task investigation above highlighted that the recovery process is concerned with the events occurring in the body primarily after a performer has completed exercise. But when and why is it important for a performer/coach to have an understanding of the recovery process? It is important to maintain a performer’s readiness to perform:
- during exercise, to allow the performer to maintain performance, for example repeated sprints during a team game
− Performer 2 is allowed 30 seconds recovery between each 10 x 10-metre shuttle sprint
− Performer 3 is allowed 180 seconds recovery between each 10 x 10-metre shuttle sprint.
record your results in Table 8 below. show the + or – time, as compared with the
performer’s first shuttle time, for the second and third shuttles, and add these together
for a total + or – time in the final column.
Table 8
Performer First 10 shuttles second 10 shuttles Third 10 shuttles Total + / - sprint times from first shuttle
**1. (+/- ) (+/- )
- (+/- ) (+/- )
- (+/- ) (+/- )**
Compare/discuss your results in relation to the rest/relief interval and each subject’s
performance and answer the following questions.
1 What happened to the performance of each subject?
2 Do any of the relief intervals allow sufficient time for a full recovery?
3 If you were trying to improve your subject’s muscular endurance, which recovery time
would you choose? Explain your answer.
4 If you were trying to improve your subject’s speed, which recovery time would you
choose? Explain your answer.
5 list three opportunities within a team game of your choice where you can allow time
for recovery.
6 how would knowledge of the recovery process be beneficial to you as a performer or
a coach?
- after exercise, to speed up their recovery in time for their next performance, for example the same or next day.
Task 9 identifies that the recovery process involves both the removal of the by-products produced during exercise and the replenishment of the fuels used up during exercise. We will identify the products that are removed and those that are replenished now as we look at the recovery process in more detail.
The main aim of the recovery process is to restore the body to its pre-exercise state; in other words, to return it to how it was before a performer started exercise.
remember
Remember the processes involved in the energy systems when considering the events taking place in the recovery process.
energy
At AS-level you saw that the body does not immediately return to resting levels after exercise, but that respiration and heart rate remain elevated during recovery. This is the key process of recovery known as excess post-exercise oxygen consumption ( EPOC ; formerly termed the oxygen debt). This excess oxygen consumption, above that of a resting level during recovery, explains why respiration remains elevated after exercise to restore the body to its pre-exercise state. Figure 16.11 shows that EPOC is thought to consist of two stages, an initial rapid recovery stage, termed alactacid debt, and a slower recovery stage termed lactacid debt.
task 9
An exhaustive bout of exercise like that completed in Task 8 causes many changes within
muscle cells, for example an increase in lactic acid. Create a table using the following
headings:
1. Changing factor 2. increase/decrease 3. Action to reverse change
1 Make a list in the ‘Changing factor’ column of any additional internal changes that you
think will take place (refer to the energy systems for some pointers to help you).
2 indicate in the ‘increase/decrease’ column if the change increases or decreases
during exercise.
3 indicate in the ‘Action to reverse change’ column what is required to reverse the changes
you have identified.
02
consumption
02 deficit
Resting 0 2 consumption
2/3 min
Time
Alactacid Lactacid
EPOC
Steady state V0 2 consumption = energy requirements of exercise
End recovery 1/2 hrs
End exercise
Exercise V0 (^2)
Start exercise
Fig 16.11 EPOC showing alactacid and lactacid stages of recovery process
KEY TERMS
excess post-exercise oxygen consumption (ePoC) The excess oxygen consumption, above that at a resting level, during recovery, to restore the body to its pre-exercise state.
Alactacid The ‘a’ before lactacid signifies it is without lactic acid.
