CHAPTER 7 Energy systems and physical activity

CHAPTER 7

CH

AP

TE

R 7

Energy systems and physical activity

The energy for muscular contractions comes from adenosine triphosphate, which is found in several sources including our food and drink. It may be released from carbohydrate, fat or protein, depending on the body’s state of activity or health.

The body produces adenosine triphosphate via three energy pathways. Each is the main provider under specifi c exercise conditions, but all contribute to energy across all degrees of activity. Each energy

system has strengths and weaknesses when compared with the others, and specifi c sporting performances exemplify each system’s majority contribution to the production of adenosine triphosphate. This chapter explores the three basic chemical pathways towards the production of adenosine triphosphate, along with their relative characteristics. The lactate threshold is a major concept in energy system theory.

CH

AP

TE

R 7

Assessment tasks

Assessment tasks Topics Page

Written report Diet assessment (activity 2) 211

Oral presentation Multi-stage fi tness test (activity 4) 218

Laboratory reports Phosphate recovery times (activity 3)Multi-stage fi tness test (activity 4)Step test (activity 5)

217218221

Data analysis Phosphate recovery times (activity 3) 217

Case study analysis Aerobic power test (activity 7) 225

Multimedia presentation Activity analysis – phosphate efforts (activity 6) 223

Report on participationin physical activity

Basketball analysis (activity 1) 211

Test Review questions 226

After completing this chapter, students should be able to:

• identify the three major energy systems that interplay during physical activity

• describe the various ways in which adenosine triphosphate (ATP) is created within the three energy systems

• explain the advantages and limitations of each of the three energy systems

• analyse how sports performance is controlled and predicted by their reliance on each of the three energy systems

• outline the causes of fatigue including the lactate threshold, energy substrate depletion and ineffi cient recovery.

210LIVE IT UP 1

Why energy?

Your body needs energy for basic body functions and activity during your whole life — energy for breathing, sleeping, digesting, sitting in a chair, sprinting for a bus, and everything else you do day and night.

The interaction between muscles and bones keeps the body upright and under control. To allow this teamwork between the muscular and skeletal systems (see chapter 5), the body needs energy sources that will permit muscles to work, for example, the effort needed by the abdominal and back muscles to enable good sitting posture, or by the muscles of the abdominals, back, legs, torso and arms during a softball game.

Adenosine triphosphate

The chemical compound adenosine triphosphate (ATP) provides the energy that allows muscular effort. ATP is the energy source for all muscular effort, whether for a small subconscious movement such as the blinking of an eye or a planned repetitious effort in weight training (see chapter 9, Live It Up 2, second edition).

Sources of ATPATP is an end product of your diet. All the food, processed drinks and water that you consume contain nutrients that your body requires for:– healthy growth– repair of body ‘wear and tear’ from everyday activities– energy for all bodily functions.

The components of a healthy diet are carbohydrate, fat, protein, vitamins, minerals and water. ATP can be created from carbohydrate, fat and protein. Chapter 11, Live It Up 2, second edition more fully explores the processes by which the body produces energy from food.

Carbohydrate

When carbohydrate is digested, it is broken down to glucose for blood trans-

portation and then stored as glycogen in the muscles and liver. Glycogen can provide the energy for ATP production under both anaerobic (no oxygen required) and aerobic (oxygen required) conditions.

Fat

Fat provides the major source of energy for long-term physical activity. During a long team game or a marathon, fat (as either triglycerides or free fatty acids) usually contributes to ATP production to meet sub-maximal energy demands. Under special conditions, the athlete may be able to use fat earlier in the activity to ‘spare’ the carbohydrate stores and therefore enable longer high-level effort. During rest conditions, fat produces the majority of the required ATP.

Protein

Protein only minimally contributes to ATP production. In extreme circum-

stances (such as starvation or ultra triathlon/marathon events) when the body has severely depleted its supplies of carbohydrate and fat, protein can become a viable source of ATP.

211CHAPTER 7 ENERGY SYSTEMS AND PHYSICAL ACTIVITY

Key knowledge• The cardiorespiratory

system: structure of

the heart and lungs,

mechanics of breathing,

gaseous exchange,

blood vessels, blood fl ow

around the body at rest

and during exercise

• Introduction to aerobic

and anaerobic energy

systems, including

aerobic and anaerobic

glycolysis

Key skills• Use correct terminology

to describe the role of the

body systems at rest

and when undertaking

physical activity.

• Observe and record how

the body systems function

during physical activity.

• Identify and discuss the

range of acute effects that

physical activity has on

the body.

• Perform, observe,

analyse, evaluate and

report on laboratory

exercises related to the

body systems.

Report on participation in physical activity

Basketball analysis

As a class, after an appropriate warm-up, play a hard game of basketball or netball. Hand out to-scale court drawings on which player movements can be plotted.1. Have the class organised into these work groups:

– players– body parameter recorders; paired off one-on-one with the players– games analysis recorders; paired off one-on-one with the players.

2. Play a number of 7–10 minute playing segments, each with an intervening 5 minute break. During the play, the games analysis recorders are to plot how far their partner has sprinted, jogged, walked and for how long they stood still in the playing segment.

3. During the breaks, the body parameter recorders are to talk with, assess and record their partners’ physical responses, including:– heart rates (polar heart rate monitors will be useful for this,

or do it manually with 10 second pulse counts)– respiration rates– observable perspiration amounts– verbal reports of fatigue levels (easy, bit puffed, tiring,

struggling, had it . . .).4. In your work groups, compile your results and address the following issues:

a Present your fi ndings in hard copy tables and/or a multimedia presentation.

b How far did your player sprint, jog and walk?

c What percentage of time did he or she spend in each of sprint/jog/walk, and for how long were they stationary?

d Plot their physical responses to the exercise segments against the other players.

e Establish a priority list of perceived fi tness among the players.f List the bases for your decisions in question e.g List the information that the class has established from this exercise

that cover fi tness, fatigue and energy.

Activity 1

The body’s storage of food fuel

Food fuel Stored as Site

Carbohydrate GlucoseGlycogenAdipose tissue (storage of excess carbohydrates)

BloodMuscle and liverAround the body

Fat Free fatty acidsTriglyceridesAdipose tissue

BloodMuscleAround the body

Protein MuscleAmino acids

Skeletal muscleBody fl uids

Table 7.1

Key knowledge• Introduction to aerobic


systems, including

aerobic and anaerobic

glycolysis

Written report

Diet assessment

Record your total diet for three days. Estimate the percentages of carbohydrates, fats and protein by using packet labelling and nutrition guides supplied by your teacher. Have a class discussion to establish how you could improve your diet to meet your energy needs.

Activity 2

212LIVE IT UP 1

Adenosine

Energy EnergyMuscle

activityFood

PP P

PP

P

Adenosine

ADP + P

ATP

Energy from ATP

ATP is stored in limited quantities within muscle, so each muscle fi bre must be able to create its own from the food fuels. Figure 7.1 illustrates how the metabolism of food creates ATP which then provides energy for muscular exertion.

ATP is an adenosine molecule with three phosphate molecules attached. When muscular activity is needed, one of the phosphate molecules breaks off, releasing energy and creating adenosine diphosphate (ADP) (see fi gure 7.1). This process is reversible: fi gure 7.2 shows how ADP can become ATP. This reversal can occur continually during the activity as long as suf-fi cient energy substrates are available. Depending on the type of physical activity (see chapter 8), energy substrates include phosphocreatine, glucose, glycogen, lactic acid, fat, protein and oxygen. These are substances the body can use to create ATP.

A muscle fi bre stores only a small amount of ATP, so the force and duration of a muscular effort is only as effective as the ATP replenishment process. During and after physical exertion, the body uses several methods of recovery to rebuild used supplies of ATP and food fuels.

Figure 7.1:

Energy for muscular activity

— from food to ATP to muscles


1

2

3

4

5

6

7

8Brain

CNS

Muscles

Adenosine

PP P

Adenosine

PP P

Adenosine

P P

Adenosine

P P

PPP

02

Adenosine

PP

Adenosine

P

02

P

P

PP

Energy

P

Adenosine

ATP for physical activity

1 Muscles have stores of ATP

ready for activity.

2 Movement is initiated

by a message from the

Central Nervous System (CNS)

to the muscle.

3 The muscle releases calcium salts

into the muscle depths that activate ATP.

4 ATP loses one of its three phosphate

molecules and thereby releases energy

for muscle contraction.

5 Muscles contract.

6 ADP amounts build as ATP diminishes.

7 During aerobic effort or during rest, spare

oxygen allows the reattachment of loose

P with the ADP, thus creating more ATP.

8 More ATP is constantly created during

rest or during the activity depending on

the intensity of the exercise.


Figure 7.2:

The cycle of ATP being broken down for muscle

movement, consequentially creating ADP, then being

reconstituted as ATP with the presence of oxygen

214LIVE IT UP 1

Energy for rest and activityThe body can create energy (ATP) under two main conditions:• rest conditions, where there is suffi cient oxygen available

for the body to continue to function at a resting level• active conditions, where physical exertion means there is

insuffi cient oxygen available for the body to continue to function at a particular level without a marked increase in oxygen intake either during or after the effort. These conditions occur during anaerobic activity and aerobic activity.

ATP production during rest conditions

Rest is when the body is not under physical stress and when breathing and heart rates are at resting levels. The body has an abundant oxygen supply, so it produces approximately two-thirds of the ATP from fat stores within the muscle and elsewhere in the body. Fat is a much richer energy source than carbohydrates. To release this energy, the body must use much more oxygen than it would in activating the supplies of ATP from glucose. When at rest, you have an abundant supply of oxygen which is above the body’s metabolic demands.

The other third of ATP needed under rest conditions comes from carbohy-

drate in blood glucose and glycogen stores within both the muscle and liver. As with fat, glycogen is broken down in the mitochondria (structures within the muscle cell, referred to as the ‘powerhouses’ of the cell) (see fi gure 7.8).

The end products of aerobic metabolism are carbon dioxide, water and heat. No by-products limit body activity; only food fuels and the rate of aerobic metabolism limit ongoing aerobic ATP production.

ATP production during activity

‘Activity’ in physical education is a broad term that covers any physical state more exertive than rest. The level of activity is determined by factors such as:• how long the activity continues — activity duration• how hard the body works during the activity — activity intensity• the level of the individual’s aerobic fi tness• the level of recovery achievable between activity efforts.

When the body starts physical activity, it immediately demands an increased oxygen supply to the working muscles. The respiratory and circu-

latory systems (see chapter 6) are unable to meet this immediate demand, so the body uses two energy pathways to create ATP anaerobically (i.e. without oxygen). These anaerobic pathways produce ATP quickly and powerfully, but they have three disadvantages:• they produce relatively small amounts of ATP• they operate for only a short period• they result in fatiguing by-products.

If the physical activity is at a reasonably sub-maximal level, then the body is able to produce the required ATP aerobically because the body’s ability to use oxygen can meet the muscles’ demands for extra oxygen for greater ATP production. This aerobic pathway has opposite qualities to those of the two anaerobic systems:• it can produce ATP for sub-maximal efforts for long periods of time• it cannot quickly produce energy for high intensity efforts• it has no toxic by-products.

The body produces ATP under these varying levels of physical activity via three energy pathways: the phosphate energy system, the anaerobic gly-

colysis system and the aerobic system.


Three energy systems

All three energy pathways operate at any one time, but the contribution of each varies depending on the intensity of the activity. Figure 7.3 illustrates the overlapping nature of the three energy systems that underpins their ‘interplay’. Note that the identifi ed percentage contribution of each energy system to exertions of different durations has changed with sports physi-ology research over the years.

Phosphate energy systemThe phosphate energy system provides the bulk of ATP during powerful or explosive efforts. Such efforts may be once-off — such as a court-length pass in basketball or a take-off in the high jump — or ongoing — such as a sprint to position in netball or football. The phosphate energy is closely linked with several fi tness components (see chapter 5, Live It Up 2, second edition).• muscular strength • anaerobic power • agility• muscular power • speed • reaction time.

Following about 10 seconds of maximal effort, the phosphate system is largely depleted and the body needs to signifi cantly reduce the activity’s intensity as the anaerobic glycolysis system begins to become the dominant provider of ATP. The phosphate energy system relies on muscle stores of both ATP and a chemical compound called phosphocreatine.

If the activity requires a maximal effort for 5–10 seconds, such as an elite 100-metre sprint event, then stores of ATP and phosphocreatine in the working muscles jointly create most of the maximal effort for that activity.

After about 10 seconds of efforts, the muscles’ stores of ATP and phospho-

creatine are greatly depleted. Thus, with critically low stores the athlete must either slow down or stop.

Once this maximal effort is over, the body is able to take in more oxygen via puffi ng. This extra oxygen is able to create more ATP from ADP, and to reconstitute phosphocreatine from the broken phosphate and creatine mol-ecules remaining after the sprint (see fi gure 7.4).

Following a 10-second maximal effort, the body can take around 3–5 minutes to fully restore the ATP and phosphocreatine supplies to pre-exercise levels within the working muscles. If the effort was less than 10 seconds, then the recovery time to pre-exercise levels is faster than 3 minutes. (Chapter 4, Live It Up 2, second edition contains more detail on this recovery process.)

Figure 7.3:

A graphic interpretation of the

three energy systems and their

periods of prominencePerformance time (seconds)

En

erg

y c

on

trib

uti

on

(%

)

Aerobic energy

Anaerobic glycolysis

Phosphate energy

25

50

75

100

0

10 30 60 90 120 180 240 300 3600

216LIVE IT UP 1

P × C

PP

Adenosine

P

Adenosine

PP P

P

P × C

P — C

P — C

P × C

Energy

P

Adenosine

P P

P

P ×C

Energy

PP

Energy

P

Adenosine

Adenosine

PP

P — C

PP

Adenosine

P

1

2

34

5

6

The phosphate system

1 The power athlete at the start of

the event, muscles primed and full of

ATP and PC stores.

2 At the starting gun, the maximal explosive

effort to leave the starting blocks

immediately uses up some of the stored

ATP in the muscles, resulting in ADP.

3 The muscle stores of PC split,

releasing energy.

4 This energy allows the single phosphate

molecules left from the spent ATP to be

reattached to the ADP creating more ATP

that allows the maximal effort to continue.

5 This replenishing process continues

while the athlete completes the race

at maximal effort.

6 The athlete crosses the finish line

with muscle stores of ATP

and PC depleted.

Adenosine

P P

Figure 7.4:

The cycle of ATP being broken down

and resynthesised for powerful

muscle movement centres around

the energy from PC splitting


Key knowledge• The cardiorespiratory system:

structure of the heart

and lungs, mechanics of

breathing, gaseous exchange,



and during exercise

• Introduction to aerobic and

anaerobic energy systems,

including aerobic and

anaerobic glycolysis



body systems at rest and when

undertaking physical activity.

• Observe and record how the

body systems function during

physical activity.

• Identify and discuss the range

of acute effects that physical

activity has on the body.

• Perform, observe, analyse,

evaluate and report on

laboratory exercises related

to the body systems.

Laboratory report and data analysis

Phosphate recovery times

As a class, choose half the class to thoroughly warm up and then attempt a series of 25-metre swimming sprints. Allow gradually reduced recovery periods after each sprint: 5 minutes, 3 minutes, 1 minute and 10 seconds. Each subject should take their heart rate for 10 seconds after each sprint. If you are not a test subject, help organise and record the sprints.1. Graph (by plotting it on graph paper or by using

graphing software) and discuss the results.2. Write a report in which you explain the peak time for the

phosphate energy system, its required recovery period and how the laboratory demonstrated the theory.

Activity 3

Anaerobic glycolysis systemThe anaerobic glycolysis system is also known as the lactic acid system. This system mainly provides the bulk of ATP production during high-

intensity, sub-maximal efforts. It may also become the dominant producer of ATP during repeated phosphate efforts which have insuffi cient recovery time to allow full phosphocreatine replenishment. Muscle stores of glycogen are anaerobically broken down during effort to release energy for ATP to be resynthesised from ADP.

The anaerobic glycolysis system operates as the dominant supplier of ATP in the period from around 10 seconds of maximal effort to around 60 seconds. Most recent studies suggest that the overlap period — when the body switches from using the anaerobic glycolysis system as the dominant ATP producer to using the aerobic system — could start as early as 30 seconds into high-level, sub-maximal activity (see fi gure 7.3).

The anaerobic glycolysis system is closely linked with several fi tness components (see chapter 5, Live It Up 2, second edition):• anaerobic power• local muscular endurance• speed• muscular power.

218LIVE IT UP 1

Figure 7.5:

Jana Pittman running another 400-metres hurdles race.

Her efforts produce large amounts of lactic acid.

Key knowledge• Introduction to aerobic and




Key skills• Use correct terminology to

describe the role of the body

systems at rest and when


• Observe and record how the

body systems function during

physical activity.






laboratory exercises

related to the

body systems.

Laboratory report and oral presentation

Multi-stage fi tness test

As a class undertake the multi stage fi tness test (see chapter 6, Live It Up 2, second edition).1. Stop when you reach what you think is your lactate

threshold.2. Record your HR at this time.3. Note the reasons why you have picked this stage of the test.4. Could you have kept running? Give some reasons.5. For how long?

6. Was the level you reached the best you have done for this test?

7. Write up your responses to the class’s efforts and share these with the class in an oral report.

Activity 4

It is classically exemplifi ed in the 400-metre run in secondary school athletics, but it is also highly relevant in a team game when the performer is required to undertake repeated sprints that do not provide suffi cient

recovery time for the phosphate system. Most players in team games can relate to a situation of having insuffi cient energy to allow continued top effort, and thus needing a time-out or a rest on the substitution bench.

Because the anaerobic system operates without oxygen being used for ATP production, lactic acid (LA) is produced as a by-product. This

affects the muscles’ ability to contract and creates fatigue in the per-

former. If the performer tries to continue exercising at the same anaerobic intensity, the levels of lactic acid increase and will cause the individual to either slow down or stop.

As the individual tries to continue exercising at this high anaerobic inten-

sity while fi ghting the fatigue caused by the lactic acid, they will reach what is known as their lactate threshold. This is the level at which the lactic acid levels prevent their ability to continue working at the same intensity.

During 20 minutes of a football or netball game, an involved player may carry out over 100 power (or phosphate) efforts. Even if adequate oxygen-

rich recovery conditions are available between each effort, there is still only around 10 seconds for recovery each time. Therefore, the phosphate energy system usually becomes severely depleted in sources of ATP production, and the next quickly available system (anaerobic glycolysis) takes over as the dominant ATP supplier.

During a 400-metre run, lactate accumulation affects the runner during the home straight but can generally be endured until the race fi nishes. A team game is quite a different situation: the lactate threshold cannot be ignored.


ADP + PC

ATP

ADP + glycogen

ATPNo O2

ADP + glycogen

ATPNo O2

ADP + glycogen

ATPNo O2

ADP + glycogen

ATPO2

LA

LA

LA

LA

Adenosine

PP

P ×C

The anaerobic glycolysis system

1 On blocks at start of 400 m race.

2 At 15–20m point. ATP–PC system

is depleted. Anaerobic glycolysis

system now becoming dominant

ATP supplier.

3 End of back straight at 200 m mark.

Cruising, feeling good.

LA increasing in blood stream, but

not noticeable.

4 Entering home straight, about 80 m

from home. Increasing LA levels

beginning to be uncomfortable.

5 Building LA levels do not prevent

finishing the race, but do cause

a slowing down during the last

80 m of the race.

6 Much puffing after the race

helps reduce LA levels to

resting values within the

next half hour or so.

1

2

34

5

6

Figure 7.6:

Anaerobic glycolysis is best

exemplifi ed in the 400 m run. It

provides most of the needed ATP

but produces lactic acid.

220LIVE IT UP 1

ADP + glycogen

ATPO2?

ADP + glycogen

ATPO2

LA

LA

P

Energy

P

Adenosine

P

02

Adenosine

P P

P

1

2

3

4

5The aerobic glycolysis system

1 Start of 20 minute cross-country race.

2 Low sub-maximal effort with HR

around 70–80 per cent of maximum.

3 Sufficient O2 levels allow ATP to be

continuously replenished from ADP.

4 Any periods of acceleration or hill work

will increase LA levels, but are generally

controlled by following periods of lower

exertion where O2 supplies become

plentiful again.

5 At end of race, fatigue is generally

from joint fatigue, dehydration,

mental fatigue, higher than normal

LA levels or reduced muscle glycogen.

ADP + glycogen

ATPO2

Figure 7.7:

Aerobic glycolysis is best

exemplifi ed in any longer

aerobic effort. It provides the

vast bulk of the required ATP.

Aerobic energy systemThe aerobic energy system is also known as aerobic glycolysis. It is relevant to all of the fi tness components because it provides either the basis for recovery between strength and power efforts, or the bulk of energy for sub-

maximal efforts.Aerobic glycolysis, as with all the energy systems, contributes to ATP

production under all conditions. However, it contributes the majority of ATP during continuous sub-maximal activities that go beyond 1 minute.

With the rich oxygen supplies in the aerobic system, fat is able to become a signifi cant contributor to ATP production. Fat requires a complex series of reactions that depend on oxygen within the muscle cell’s mitochondria. Protein is similarly metabolised for ATP production, but only under extreme conditions.

The body’s supply of fat exceeds even the physical requirements of a highly trained athlete, so the aerobic system could theoretically operate for an unlimited work period.




systems, including aerobic

and anaerobic glycolysis

• The cardiorespiratory system:

structure of the heart

and lungs, mechanics of

breathing, gaseous exchange,



and during exercise

Key skills• Use correct terminology to

describe the role of the body

systems at rest and when










laboratory exercises related to

the body systems.

Laboratory report

Step test

If they are available use Polar HR monitors. If not, work in pairs and take HR manually.

Sit quietly on some benches in the physical education centre at school, and put on a heart–rate monitor. Check the monitor is displaying your heart rate. Do not talk or walk around. Concentrate on breathing slowly and evenly. Take note of your heart rate after sitting quietly for three minutes. Record your heart rate.

Begin the test under your teacher’s directions: step up and down on the bench at a set rhythm that allows you to complete a full stepping sequence each fi ve seconds, or 20 sequences per minute. Put your left foot up, right foot up, left foot down, right foot down . . . and so on. When both legs are on top of the bench, both legs should be straight.

Continue stepping until told to stop and then sit down on the bench.

After 5–10 seconds record your heart rate and continue to record every 30 seconds for fi ve minutes. Record all measurements on the sheet.

Complete the table below with your results after you fi nish exercising.

Graph your results. Answer the following questions:1. What was your maximum heart rate at the end

of the step-up exercise?

2. On the same graph draw the results of another subject. Clearly label both graphs.

3. Compare the two graphs. Which subject’s heart rate dropped the greatest distance?

4. Who do you think is fi tter for this exercise?

5. What evidence could you give to support this?

6. What factors control resting, exercise and recovery heart rates?

Activity 5

Time 00 sec 30 sec 1.00 min 1.30 min 2.00 min 2.30 min 3.00 min 3.30 min 4.00min 4.30 min 5.00 min

Heart rate

Figure 7.8:

The mitochondrion

carries out aerobic glycolysis,

involving glycogen breakdown

with oxygen present. Also, both fat

and protein may be metabolised.

Mitochondrion

Glycogen

GlucoseATP

Pyruvic acid

Fat ProteinOxygen

HydrogenCitric acid cycle

Carbon dioxide ATP

Electron transport chain

Water

222LIVE IT UP 1

Table 7.2

Summary of the three energy systems Characteristic

Phosphate

energy

Anaerobic

glycolysis

Aerobic

glycolysis

1. Energy source for ATP production

Phosphocreatine CarbohydrateGlycogen

CarbohydrateFatProtein

2. Duration of dominant energy production

5–10 Seconds 30–45 Seconds >60 seconds

3. Recovery time until repeat effort

Phosphocreatine replenishment: 3–5 minutes

Removal of lactic acid to rest levels:

• With active recovery: – 95% removal:

30 minutes

Restoration of body glycogen stores:

• 6–48 hours

4. Limiting factor when operating maximally

Depletion of phosphocreatine

Lactic acid accumulation

• Lactic acid accumulation

• Lower glycogen stores

• Dehydration

5. Intensity and duration of activity where the system is the dominant ATP provider

Maximal intensity (>95% max hr) and duration of 1–10 seconds

High, sub-maximal intensity (85–95% max hr) and duration of 10–30 seconds

Sub-maximal intensity (<85% max hr) and duration of >30 seconds

6. Specifi c sporting examples

• any athletic fi eld event

• elite 100 m athletic sprint

• golf drive• gymnastic vault• volleyball spike• high mark

and long kick in AFL

• tennis serve• water polo

centre forward-

centre back contest

• 200–400 m in athletics

• 50 m swim• consecutive

basketball fast breaks• high intensity

15–20 second squash rally

• repeated leads by AFL full forward

• elite netball centre in close game

• quadriceps in downhill skiing

• water polo consecutive fast breaks and defends

• marathon• cross-country

skiing• triathlon• AFL mid fi eld• hockey wing• all elite team

players• rowing

2000 m race• water polo

game

7. Everyday activity examples

• running up one fl ight of steps

• carrying heavy shopping from car to house

• sprinting for train

• running up four fl ights of stairs

• running 200 m to catch bus

• chopping wood• moving heavy

furniture

• shopping• going to the

cinema• gardening• mowing lawn• dancing• ironing• studying


Key knowledge• Introduction to aerobic and




Key skills• Observe and record how








laboratory exercises

related to the body systems.

Multimedia presentation

Activity analysis — phosphate efforts

Watch a replay of any high-level team game, then assign groups to record all phosphate efforts by the players.1. Assess the average length of each effort and the average

recovery time between each.2. Determine the relative importance of each of the three

energy systems to the game.3. Display your percentages in pie charts and as a

PowerPoint presentation.

ATP production — different exertion conditions

The length and intensity of physical exertion determine which of the energy systems is the dominant contributor to ATP production (fi gure 7.9). As the activity time increases, the infl uence of the aerobic system on ATP production also increases. However, the relative contribution of each of the three energy systems varies according to the intensity and duration of the activity.

Activity 6

6 seconds

6.3%

44.1%

49.6%

30 seconds

30%

20%

50%

60 seconds

50%

50%

120 seconds

65%

35%

1 hour

92%

8%

4 hours

50%

50%

ATP

Creatine-phosphate

Anaerobic glycolytic

Aerobic glycolytic

Aerobic lipolytic

Figure 7.9:

The average energy contributions

of different energy systems during

high-intensity competition

Source:

Burke, L. and Hawley, J. 1998,

Peak performance: training

and nutritional strategies

for sport, Allen and Unwin,

St Leonards, p. 47.

224LIVE IT UP 1

Aerobic system

Anaerobic systems

LA

accum

ula

tion m

mo

l/L

Exercise intensity

4

Figure 7.10:

The aerobic and anaerobic

contributions to ATP production

as exercise intensity increases.

The lactate threshold is the point

at which lactic acid production

affects performance.

Onset of blood lactate accumulation

OBLA is the acronym for the onset of blood lactate accumulation. At rest, everyone has lactic acid (LA) in their muscles. It is only when exercise begins that the muscular levels of LA begin to rise. If the exercise or activity is anaerobic in nature, then the levels of LA rise more signifi cantly.

At the early stages of anaerobic work, the rising muscular concentrations of LA easily fl ow from the working muscles through the capillary walls into the circulatory system. This increase in blood levels of LA is the signal that OBLA has occurred. This is easily measured at elite training venues such as the AIS in Canberra where technological facilities and sports scientists are available to quickly take and measure blood samples from athletes. When these readings are combined with an athlete’s record of physiological responses to exertion, training can be tightly geared around his or her lactate threshold.

Lactate threshold

Lactate threshold is the common term used at the elite level of sports physi-ology. It is the point above which lactic acid begins to rapidly accumulate in the blood, and below which blood levels of lactic acid do not inhibit effort at the desired level.

Beyond the lactate threshold, muscle and blood lactate levels exponentially increase and the athlete has to reduce or stop muscle effort. For untrained people, the lactate threshold is usually around 4 mmol/L, (mmol/L — the measure of how many units of LA are present in one litre of blood).

Trained athletes can increase their tolerance to LA accumulation and are able to continue effective performance or training with much higher lactate levels in their working muscles and circulatory system.

At the AIS, athletes’ LA levels have been measured at above 20 mmol/L while continuing to effectively train or compete anaerobically.

Once the athlete passes the lactate threshold and continues the activity until reaching exhaustion, all energy systems are still functioning but the body’s increasing reliance on the anaerobic glycolysis system results in lactic acid levels that curtail the activity.

Figure 7.10 indicates there is no exact physical state at which the lactate threshold occurs. It will differ with each individual, the individual’s state of fi tness and the intensity of the activity. However, some indicators (which vary in their precision) provide coaches and athletes with a means of assessing the effort required by a work-out (table 7.3).


Lactic acid removalExisting exertion levels determine the rate of lactic acid removal. An active recovery provides the best conditions, with exertion levels less than the level of the lactate threshold, and with a heart rate ideally 15–30 beats per minute lower than that at the lactate threshold. With blood fl ow greater than at rest levels, the blood fl ow through the muscle capillaries is still substantial enough to disperse lactic acid.

The bulk of lactic acid is converted back to ATP inside the mitochondria creating new ATP supplies. Once exercise is fi nished, the liver can also reconvert lactic acid to glycogen. The body also deals with small amounts of lactic acid through respiration, perspiration and excretion.

Ways of determining the lactate threshold

Method Determinant

1. Percentage of maximum heart rate

Untrained athlete — around 60%

Trained athlete — around 90%

2. Blood lactate levels Untrained athlete — 4 mmol/L

Trained athlete — more than 4 mmol/L

3. Conversation during exercise

Ability to talk continues, but extended conversation is uncomfortable.

4. Respiration Breathing rate is still comfortable at the onset of blood lactate accumulation but becomes more rapid as effort continues past it.

Table 7.3









physical activity.




• Identify and discuss

the range of acute effects

that physical activity

has on the body.



laboratory exercises related

to the body systems.

Case study analysis

Aerobic power test

Select two high-level endurance athletes from the class and obtain a medical clearance for each.1. Design an aerobic power laboratory test on bikes or treadmills

that can be continued to maximal levels.2. Ensure you can record accurate heart rates. Use Polar HR monitors.3. Predict when the onset of blood lactate accumulation is likely

to occur for each of the two subjects.4. Have the subjects perform the test until they have to stop,

recording as many body responses as possible during the test.5. Try to pinpoint when the onset of blood lactate accumulation

occurs. Give reasons for your decision.6. Try to notice when the lactate threshold occurs.7. Assess the value of the test and answer questions your

teacher will prepare. Some possible areas to investigate include: levels of oxygen consumption during the test; the percentage contributions of each energy system; differences in the onset of blood lactate accumulation for each subject; reasons for respiration rates and other body responses to the test.

Activity 7

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Chapter summary• The energy for physical activity is released by adenosine triphosphate

(ATP).• This energy source is stored in only small amounts within muscles,

so the body must continually reproduce it for continued muscular effort.• ATP is produced via three energy pathways:

– the phosphate energy system, which uses phosphocreatine to create new ATP supplies without oxygen

– the anaerobic glycolysis energy system, which uses glycogen but no oxygen

– the aerobic energy system, which uses primarily glycogen and fats (and protein under extreme conditions) to create ATP.

• The phosphate energy system can create ATP very quickly, with a major energy contribution to powerful exertions of up to around 10 seconds duration. It depletes quickly, taking around 3–5 minutes to replenish.

• The anaerobic glycolysis system takes longer to create ATP. It is the major contributor to high-level exertions of 10–60 seconds, but creates lactic acid as by-products.

• The lactate threshold is the stage when lactic acid concentrations within the blood reach the level at which continued high-level muscle activity cannot continue.

• It can take up to 60 minutes to restore lactic acid to resting levels.• The aerobic glycolysis system becomes the major contributor to muscle

activity from around 60 seconds into a sustained sporting performance. It relies on an effi cient circulo-respiratory system.

• The aerobic creation of ATP within the muscle occurs in the mitochondria.

Review questions1. Defi ne in your own words the key terms listed below, all of which appear

in this chapter. When you have fi nished, check your defi nitions with those in the glossary on page 285:

adenosine triphosphate (ATP)adipose tissueaerobic glycolysisanaerobic glycolysiscarbohydrate (CHO)energy substratesfatglucoseglycogen

lactate thresholdlactic acid (LA)mitochondrionmmol/L of LAOBLAphosphate energy systemphosphocreatine (PC)protein

2. In class, discuss the following sports or individual events and predict, using pie charts, the relative importance of each of the three energy systems in the successful completion of the activity. Assume they are being performed by elite adult sportspeople:(a) netball(b) cricket(c) Australian Football(d) high jump(e) gymnastics fl oor routine(f) rowing — 2000 m race(g) 400 m run(h) 25 m swim.





• The cardiorespiratory

system: structure of the

heart and lungs, mechanics

of breathing, gaseous

exchange, blood vessels,

blood fl ow around the body

at rest and during exercise





physical activity.




• Identify and discuss the

range of acute effects

that physical activity

has on the body.


evaluate and report

on laboratory

exercises

related to the

body systems.

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3. Explain the differences between OBLA and the lactate threshold.4. What would be the recovery times between one elite performance

of the following efforts and a repeat effort?(a) a long jump in athletics(b) a clean-and-jerk lift in a weight-lifting competition(c) an 800 m race in athletics(d) a 100 m race in swimming(e) an Olympic distance triathlon(f) a 100 m athletic heat and the semi fi nal(g) a netball game

5. How does the body deal with the high lactic acid levels created by a high level sub-maximal effort?

Useful websites

Aerobic energy system —www.brianmac.demon.co.uk/siteindx.htm

Energy systems, aerobic and anaerobic —http://predator.pnb.uconn.edu/beta/virtualtemp/muscle/exercise-folder/muscle.html

Lactate physiology and sports training —www.lactate.com/eslact1c.html

Body systems —http://sln.fi .edu/biosci/systems/systems.html

The lactate threshold —http://home.hia.no/~stephens/lacthres.htm

www.sport-fi tness-advisor.com/anaerobicthreshold.html

Major muscle groups and microscopic structure —www.anatomy.usyd.edu.au/mru/lectures/

Muscle biochemistry —http://web.indstate.edu/thcme/mwking/muscle.html

Muscle physiology homepage —http://muscle.ucsd.edu/musintro/struct.shtml

Muscles —www.e-muscles.net/

Nismat exercise physiology corner: muscle physiology primer —www.nismat.org/physcor/muscle.html

CHAPTER 7 Energy systems and physical activity

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Transcript of CHAPTER 7 Energy systems and physical activity