Transcript Energy systems

The body’s response
to physical activity
Chapter overview
Energy
 Adenosine triphosphate
 Energy systems
 Fatigue and recovery
page 125
page 127
page 142
Training effects
 Immediate physiological responses to training
 Long-term physiological effects of training
page 146
page 146
Now that you’ve finished … answers
Energy
Page 125

Humans obtain chemical energy
from the food that we eat, and
energy from food is measured in
kilojoules

The energy gained from the
breakdown of food is used to make
a chemical compound called
adenosine triphosphate.
Adenosine triphosphate
Page 125
Figure
4.2
Figure
4.3



When ATP is broken down, releasing the final phosphate group
in the chain, it releases energy.
ATP is broken down into adenosine diphosphate (ADP) (see
Figure 4.3).
A great deal of energy is released when this bond is broken and
this provides the energy that powers the human body. It provides
energy for all processes, from breathing and digestion through to
muscle movement.
Carbohydrates
Carbohydrates are broken down by the body into glucose. The
glucose is then stored in the muscles and liver as glycogen, which
is a ready source of energy. Chemical reactions involving the
breakdown of glucose (glycolysis) or glycogen (glycogenolysis)
then produce ATP.
Fats




Fat is stored as triglyceride in both adipose tissue (fatty tissue)
and the muscles.
Triglycerides are broken down in a process called lipolysis.
Free fatty acids are the primary energy source when fat is used
for energy.
Adipose triglycerides are used if exercise is prolonged at a low
intensity.
Proteins
Under normal conditions, protein is not used to produce ATP.
During extreme conditions (for example, starvation or prolonged
exercise), protein will be used as a fuel source to produce ATP.
Energy systems
Page 127
ATP is produced using one of three energy systems:
1.
the alactacid system (also called the phosphagen or ATP–PC
system)
2.
the lactic acid system (also called the anaerobic glycolysis
system)
3.
the aerobic system.
The alactacid and lactic acid
systems resynthesise ATP
anaerobically, whereas the
aerobic system resynthesises
ATP aerobically.
Alactacid System

High intensity activities lasting for less than 10 seconds use this
system as the primary source of energy.

The amount of PC in muscles is limited. After about 5–10
seconds of strenuous work, it runs out.
Lactic Acid System



The energy released in the breakdown of glucose is used to fuel
the recombination of ADP and P to form ATP.
If the body continues to use the lactic acid system, as the
glucose is broken down to form energy, lactic acid is produced.
The lactic acid system provides a relatively quick supply of ATP,
and is an important energy source for intense, short bursts of
activity (usually 30–60 seconds, but can be up to 3 minutes).
<insert fig 4.9>
Personal reflection
Have you ever experienced
lactic acid build-up? If so,
how did your body respond
and how long did it take to
recover?
Aerobic System
The aerobic system allows the body to use carbohydrates, fats
and proteins as the fuel to produce ATP aerobically.
• Carbohydrates are broken down in a process called aerobic
glycolysis. Carbohydrates are the preferred fuel as their
breakdown requires the least amount of oxygen.
• The breakdown of fats (oxidisation) requires significantly more
oxygen to produce the same amount of ATP than the breakdown
of carbohydrates. Fats are the preferred fuel only during lowintensity exercise.
• Protein will usually be used as an energy store only in extreme
situations.
A comparison of the three ATP-replenishing energy systems
System
Source of fuel
Duration of
system
Cause of fatigue Efficiency of
ATP production
Phosphocreatine
(PC)
Up to 10 seconds Depletion of PC
stores
Rapid but limited
Glucose and
glycogen
Up to 3 mins
Build-up of lactic
acid in the
muscles
Rapid but limited
Carbohydrates,
glucose and
glycogen, fats,
protein
Indefinite at low
intensities
Depletion of fuel
sources
Slow but
unlimited
Anaerobic
Alactacid system
(ATP–PC)
Lactic acid
system
Aerobic
Aerobic system
Source: Adapted from ML Foss and SJ Keteyian, Fox’s Physiological Basis for Exercise and Sport, 6th edn,
WCB/McGraw-Hill, Boston, 1998
Integration
Consider the energy systems
contributing to the physical
activity you are currently
participating in.
1. Describe the contributing energy
systems.
2. Justify how and in what order
energy is provided for the duration
of the activity.
Energy systems in practice
Duration
10
30
 <insert table 4.2>
of event
secs secs
60
secs
2 mins 4 mins 10
mins
30 mins 60
120 mins
mins
Anaerobic 90%
80%
70%
50%
35%
15%
5%
2%
1%
Aerobic
10%
20%
30%
50%
65%
85%
95%
98%
99%
Event
(run)
100 m
200 m
400 m
800 m
1500 m 5000 m 10 000 m
ATP–PC/LA
ATP–PC/
LA/aerobic
Marathon
Aerobic
Source: Adapted from ML Foss and SJ Keteyian, Fox’s Physiological Basis for Exercise and Sport, 6th edn,
WCB/McGraw-Hill, Boston, 1998 and SK Powers and ET Howley, Exercise Physiology: Theory and Application to
Fitness and Performance, 3rd edn, Brown and Benchmark, Madison, 1997
Various sports and their predominant energy systems
Relative contribution of each energy system (%)
Sport or activity
ATP–PC and
anaerobic
glycolysis
Anaerobic
glycolysis and
aerobic
Aerobic
1 Aerobic dance
2 Baseball
3 Basketball
4 Hockey
5 Football
6 Golf
7 Gymnastics
8 Rowing
9 Skiing
a Slalom, jumping
b Downhill
c Cross-country
15–20
80
60
50
90
95
80
20
5
15
20
20
10
5
15
30
75–80
5
20
20
Negligible
Negligible
5
30
80
50
5
15
30
10
5
20
85
Various sports and their predominant energy systems
Relative contribution of each energy system (%)
Sport or activity
ATP–PC and
anaerobic
glycolysis
Anaerobic
glycolysis and
aerobic
Aerobic
10 Soccer
a Goalie, wing, strikers
b Halfbacks or sweeper
60
60
30
20
10
20
11 Swimming and diving
a Diving
b 100-m swim
c 400-m swim
d 1500-m swim
98
80
20
10
2
15
40
20
Negligible
5
40
70
12 Tennis
70
20
10
13 Walking
Negligible
5
95
Source: Adapted from ML Foss and SJ Keteyian, Fox’s Physiological Basis for Exercise and Sport, 6th edn,
WCB/McGraw-Hill, Boston, 1998
How the body obtains and uses oxygen

Highly trained endurance athletes
have efficient respiratory and
cardiovascular systems.
How the body obtains and uses oxygen
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
Oxidative capacity refers to the muscles’ ability to obtain and use
oxygen.
Athletes with a high proportion of muscles will be better able to
produce energy from ATP aerobically as greater muscle mass =
greater mitochondria.
Steady state

A ‘steady state’ is when the oxygen supply meets the body’s
demands.
VO2 max
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An individual’s highest possible oxygen consumption during
exercise is known as the volume of maximum oxygen (VO2
max).
The body’s ability to deliver and use oxygen is the main factor
determining VO2 max.
Other factors determining an individual’s VO2 max include:
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Genes
Age
Gender
VO2 max comparisons by sport and by gender
VO2 maximum
Men
Women
Basketball
40–60
43–60
Cycling
62–74
47–57
Gymnastics
52–58
35–50
Rowing
60–72
58–65
Soccer
54–64
50–60
Swimming
50–70
40–60
Track and field –
60–85
50–75
running
Source: Brian Mackenzie, UK Athletics Level 4 Performance
Coach; www.pponline.co.uk
Anaerobic and aerobic training thresholds
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During exercise, heart rate, ventilation and blood lactate all
increase in proportion to the exercise.
The anaerobic threshold can be defined as that workload
intensity (or level of oxygen consumption) when lactic acid starts
to accumulate in the blood and muscles.
The threshold is the maximum
speed or effort that an athlete
can maintain and have no
increase in lactic acid.


The aerobic training threshold is the intensity at which an
athlete needs to work to produce an aerobic training effect or a
physiological improvement in performance.
This occurs at about 70 per cent of the person’s maximum heart
rate, or at approximately 50–60 per cent of that person’s VO2
max.
Fatigue and recovery
Page 143
Fatigue
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Three areas of the body can account for the physical fatigue: the
central and peripheral nervous systems, muscle fibres and
energy systems.
Fatigue can also be caused by psychological and environmental
factors.
Recovery
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Rest recovery is a period of no movement.
Active recovery includes performing light tasks, such as slow
running, walking, stretching and minor games.
After an all-out exhaustive effort, an active recovery is
recommended to restore ATP–PC stores and to remove lactic
acid.
Recovery times for various physiological functions
Function
With active recovery
With rest only
Restoration of ATP–PC
2 minutes
5 minutes
Increase in oxygen consumption
3 minutes
6 minutes
Replenishment of muscle glycogen
10 hours
46 hours
(continuous exercise)
Replenishment of liver glycogen
5 hours
24 hours
Reduction of lactic acid in muscles and blood
30–60 minutes
1–2 hours
Restoration of oxygen stores
10–15 seconds
1 minute
Source: Adapted from ML Foss and SJ Keteyian, Fox’s Physiological Basis for Exercise and Sport, 6th edn,
WCB/McGraw-Hill, Boston, 1998
Fuel depletion and recovery
Predominant
energy system
ATP–PC
Likely causes of fatigue
Types of recovery
Fuel depletion, ATP and PC
Rest recovery
Lactic acid
Accumulation of metabolic by-products
•
H+ (hydrogen ions
•
Pi (inorganic phosphates)
NB: Lactic acid is no longer thought to
contribute to fatigue. In fact, it is being
regarded more as appositive
performance enhancer rather than a
negative.
Fuel depletion
•
Glycogen stores, then fats
•
Elevated body temperature
leading to :
– dehydration
– blood flow away from muscles
Non-dietary
•
Active recovery
•
Massage
•
Water-based therapies, e.g.
contrasting via hot/cold baths
Aerobic
Dietary
•
High GI foods
•
Rehydration via sports drinks:
– Hypertonic to replace glycogen
– Hypotonic to replace lost fluids
Non-dietary
•
Active recovery
•
Massage
•
Water-based therapies, e.g.
contrasting via hot/cold baths
Source: R Malpeli and A Telford, A+ Phys Ed Notes: VCE Physical Education Units 3&4, Nelson Australia, Sth Melb., 2008
Oxygen deficit
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The lactic acid energy system accumulates lactic acid that has to
be broken down.
Breaking down lactic acid and resynthesising depleted PC
requires oxygen during recovery.
The difference between the amount of oxygen the body uses
when truly at rest and the amount of oxygen used when exercise
has just stopped is called the oxygen deficit. Oxygen deficit is
also referred to as ‘oxygen debt’, ‘recovery oxygen’ and ‘excess
post-exercise oxygen consumption’ (EPOC).
Personal reflection
Have you ever been short of
breath after exercise? What
did it feel like? At what
level of intensity were you
working?
Training effects
Page 146
Immediate physiological responses to training
Page 146
Immediate physiological responses to training


Heart rate, ventilation rate, ventilation depth, stroke volume,
cardiac output and lactate levels increase.
Muscles contract and different muscle types are recruited.
Long-term physiological effects of training
Page 146
Long-term physiological responses to training
Increases
Decreases
Stroke volume and cardiac output
Resting heart rate
Oxygen uptake and lung capacity
Haemoglobin level
Muscle size
Muscle fibre type being trained
Now that you’ve finished …
Answers
1. Explain how ATP provides energy for muscle contractions.
The energy in ATP is stored between the phosphate bonds. When
a muscle needs to contract, a phosphate bond is broken off from
the ATP molecule, releasing the energy it needs to make that
contraction.
2. Describe the relationship between the breakdown of each of the
nutrients and the intensity and duration of exercise.
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
Carbohydrates are broken down easily and can be used to
provide energy in high intensity exercise for moderate durations.
Fats are more difficult to break down but produce more energy.
This makes them suitable for lower intensity exercise that does
not require energy to be produce quickly. Due to the large
amount of energy that is produce from each fat molecule,
exercise can be prolonged using this fuel source.
Proteins are only used in times of starvation or after prolonged
exercise where fats and carbohydrate stores are depleted. It is
difficult to break down proteins so the intensity and duration of
exercise using this fuel source is minimal.
3. Identify the by-products of energy production for the lactic acid
and aerobic energy systems
The lactic acid energy system produces lactic acid as a fatiguing
by-product. The by-products of the aerobic energy system include
heat, carbon dioxide and water which are easily removed from the
body without fatigue.
4. Distinguish the energy system contributions for athletes in the
following sports, events and positions:
a. hockey mid-fielder
A hockey mid-fielder would require a combination of all three energy
systems. The predominant system used would be the alactacid system.
There are many short, high intensity sprints involved in this position
with some time given for recovery of the phosphocreatine which would
enable this system to be used on and off for the entire game.
When mid-fielder is given inadequate time to replenish PC, the lactic
acid system would provide the energy needed to fuel the athlete. This
would occur when high intensity effort is prolonged or repeated with
very short rest breaks.
At times when there are stops in play or when the ball is moved to an
area of the field not controlled by a mid-fielder, the intensity of effort
would be reduced considerably, enabling the body to access the
aerobic system for energy.
4. Distinguish the energy system contributions for athletes in the
following sports, events and positions:
b. pole vault
As pole vault is an event requiring high intensity effort lasting less
than 8 seconds, the energy system used by such an athlete would
be the alactacid system. The rest period between attempts would
use the aerobic system and during this time, the phosphocreatine
stores would be replenished allowing for repeated maximal effort.
4. Distinguish the energy system contributions for athletes in the
following sports, events and positions:
c. equestrian
The dominant energy system for equestrian events would be the
aerobic system. The rider needs to stay calm and let the horse do
the work. Even though muscular strength is required, the major
energy system is aerobic. Equestrian events can range from 5
minutes in dressage and show jumping, to 24 hours in enduro
events. During enduro events, there is a small contribution of the
lactic acid system when the rider needs to dismount and run up
hills to conserve the horse’s energy.
4. Distinguish the energy system contributions for athletes in the
following sports, events and positions:
d. 200-metre freestyle.
The lactic acid system would be the predominant system for this
event, although all three systems would contribute. As this event
requires a maximal, all out effort, the alactacid system would be
used at the beginning of the race until the phosphocreatine is
depleted after about 8 seconds. The lactic acid system would
supply the energy where intensity is high but PC is not available.
Once lactic acid begins to accumulate in the muscles (anaerobic
threshold) the swimmer would be forced to slow down and the
aerobic system would be able to supply the energy. When each of
these systems is used would vary depending on the race strategy
of the swimmer.
5. Outline the factors affecting an individual’s oxygen consumption
and delivery.
An athlete’s heart and lung function impact upon oxygen
consumption and delivery. Oxygen uptake is dependent upon the
stroke volume (how much blood is pumped from the heart each
beat), lung capacity (the amount of oxygen that can move in and
out of the lungs each breath) and the amount of haemoglobin
(oxygen-carrying molecules) in the blood.
6. Explain the concept of VO2 max.
VO2 max is the maximum volume of oxygen an individual can
consume in any one minute.
7a. Outline the adaptations that can occur as a result of aerobic
training.
Increased number of breaths per minute, increased size of the
lungs, increased number of capillaries in the lungs, increased size
of heart, ventricles and ventricle walls, increased blood volume,
increased haemoglobin, increased muscle size, increased number
of capillaries in muscle fibres.
7b. Explain how these adaptations lead to an improvement in
performance.
Increasing the number of breaths per minute combined with a
larger lung size, enables more oxygen to be breathed into the
lungs and increased capillaries in the lungs combined with
increased haemoglobin for carrying oxygen in the blood allows
more oxygen to be absorbed into the bloodstream. Once in the
bloodstream, the ability of the heart to pump this oxygen quickly to
the working muscles can be improved by the increased size and
strength of the heart causing stronger pumps of the heart. An
increased number of capillaries in the muscles allows this oxygenrich blood to be delivered more quickly and efficiently to the
working muscles. By increasing the size of muscles, the strength
of the muscles and their ability to carry out work will improve.
8. Predict three physiological adaptations that could occur from long-term
strength training.
Muscle hypertrophy (increasing the size of the muscle) is a result of:
1.
An increase in the size of the muscle fibres due to an increase in the
number of muscle fibrils. After strenuous exercise, muscle fibrils will
split into two. Each half of the muscle fibril will grow to the size of the
parent fibril, hence, an increase in size.
2.
Muscle fibres will also increase in size due to the increased storage
of glycogen, adenosine triphosphate and phosphocreatine.
3.
Slow twitch and fast twitch muscle fibres cannot be changed, but
each can take on the characteristics of each other through specific
training.
4.
Muscle fibres can contract with greater force (an increase in the
number of actin and myosin filaments which will have an increase in
cross bridges required for contraction).
9. Explain the difference between sub-maximal exercise and maximal
exercise.

Sub-maximal exercise is exercise performed at a level that leaves the
heart rate in a plateau (a consistent rate for an extended period of time)
below its maximum number of beats per minute. Generally, this level of
exercise can be maintained for more than 20 minutes at a time.
Maximal exercise, however, is activity that leads to a heart rate that
approaches its maximum level and is hard to maintain for a long period
of time.
10. ‘Elite athletes are born, not made.’ Using your knowledge of muscle
fibres, justify your opinion about this statement.

There are 3 types of muscle fibres: red slow-twitch fibres, which contain
a large number of capillaries and produce a large amount of ATP
slowly; red fast-twitch fibres, which contain some capillaries and can
rapidly produce ATP but fatigue faster than slow-twitch fibres; and white
fast-twitch fibres, which contain few capillaries and rapidly generate
ATP anaerobically. Although an increase in muscle fibre size and
number can be a physiological adaptation to long-term training, an
individual’s genetic make-up determines their proportion of muscle fibre
type and consequently, their suitability to certain sports. An athlete, for
instance, born with large proportions of white fast-twitch fibres will be
more suited to sprinting.
Image credits
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Slide 1, Getty Images/Ian Walton
Slide 4, Getty Images/Jupiterimages
Slide 25, Australian Sports Commission