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ENERGY SYSTEMS
So we all thought energy just came
from food…
ENERGY SYSTEMS
Human body requires a continuous supply of energy both to meet the needs of its
systems and organs AND to power muscular contractions for movement.
However, unlike a car that carries fuel around in its tank – the body’s energy is stored I
chemical bonds that joins atoms and is released only as needed.
The transformation of food (chemical energy) to energy that the muscles can use
(mechanical energy) is the role od the energy systems.
FOOD & ENERGY
Energy provided by food is measured in kilojoules (kJ)
When food is digested, it breaks down to sugars, amino acids and fatty acids –
substances that become available as a usable form of energy
From these, ATP or adenosine triphosphate is produced and represents the most
important substance in energy production.
ATP can be likened to a spark plug in an engine as it enables the release of energy
where all other functions are possible.
ATP COMPOUND
The ATP compound consists of a large molecule called adenosine (A) and
three smaller molecules called phosphates (P). Each of the phosphates is held
together by high energy bonds. The chemical structure of ATP is shown below
ATP COMPOUND
When the last phosphate is detached, energy stored in bonds between the
phosphates becomes available and this is transferred to the cells. The process
is like flicking a switch. The light will not work until the current flows and
provides energy to light the globe. In muscle cells, the energy from ATP allows
the fibres to contract and make movement possible.
ATP COMPOUND
However, ATP now has only two phosphates attached. In this state it is
referred to as ADP (adenosine diphosphate) and is powerless to provide
energy.
ATP COMPOUND
Unlike food, used ATP does not become a waste product that is discharged
from the body. Instead, it has the ability to quickly rebuild and or resynthesise,
allowing us to continue to function on limited stores.
ATP needs to be continually rebuilt to enable energy flow. Under normal
conditions such as sitting, lying, only sufficient amount is produced to enable
basic function to be sustained. However, if intense physical demands such as
cycling, swimming or running are placed on the body, the systems respond by
producing much higher levels of ATP to ensure that our immediate energy
needs are met.
ATP COMPOUND
Three systems that make ATP available are:
•The Alactacid System (commonly known as ATP-PC)
•The Lactic Acid System (glycolytic system)
•The Aerobic System (oxygen system)
These systems are commonly called energy pathways because they eachy
supply ATP but use different processes to do so. Each system has their own
way of resynthesising – how well the system resynthesises ATP determines its
efficiency in energy production.
ALACTACID SYSTEM (ATP/PC)
• Supplies of ATP I the body are very limited.
• We have sufficient supply for only ONE explosive muscular contraction,
for example, a standing long jump or sprint start.
• Lasting 1-2 seconds
• An explosive movement causes ATP molecule to ‘split’ providing energy
for muscular contraction.
ALACTACID SYSTEM (ATP/PC)
• Further muscular work relies on creatine phosphate (CP)
breaking down to creatine and phosphate, and releasing energy
in the process. The energy is used to drive the ‘free’ phosphate
back to ADP so it can once again become triple phosphate.
• Once reformed, ATP can break down again – and the process
goes on.
• The problem is, however, is that CP supplies are exhausted
with 10-12 minutes and then takes 2 minutes to be restored.
SOURCE OF FUEL
• We have 90 grams (same weight as a large egg) of ATP in our body
• This is sufficient to power the muscles required in one explosive
movement such as a jump, start or throw.
• Allows for 1-2 seconds of hard work
• Following that, we rely on 120 grams of reserve fuel, CP, stored in our
cells
• Creatine phosphate, then, is the fuel of the ATP/PC system
EFFICIENCY OF ATP PRODUCTION
• The alactacid system function to ATP rapidly available. Occurs whether
or not oxygen is available.
• This is primarily possible by a concentration of CP within muscle cells
that is approximately 5 times greater than that of ATP.
• Supply of ATP is very limited if the demand is high, sustained, near
maximal or maximal.
• But the system can recover quickly.
• That is why it is integral to short, explosive movements such as weightlifting, discus throwing and sprint starts.
DURATION OF SYSTEM
• ATP supplies are exhausted after, 1-2 seconds of hard work
• CP supplies are exhausted in a further 10-15 seconds
• At rest, CP supplies are almost fully restored in 2 mins.
CAUSE OF FATIGUE
• Fatigue is caused by inability of system to continually resynthesise ADP
from CP because CP supplies are quickly exhausted.
• This is why we are unable to run at maximal effort for distances longer
than 100m.
BY-PRODUCTS OF ENERGY PRODUCTION
• No fatiguing by-products but hear is produced during muscle
contraction
RATE OF RECOVERY
• ATP/PC system recovers quickly from exercise. Within 2 minutes, most
ATP and CP supplies have been fully restored, with 50% of CP
replenishment occuring in first 30 seconds of rest recovery.
• This is why high jumpers, weight lifters and discus throwers can ‘back
up’ almost immediately after their 1st and 2nd attempts
Video: ATP & How it works
LACTIC ACID SYSTEM
• Following 10-12 seconds of maximal exercise, CP supplies are
exhausted
• ATP still needs to be produced to provide energy, assuming activity
requires effort for longer than this eg. 400m
• Oxygen is not readily available (even though breathing rate has
increased) as it takes time for the blood to move fro lungs around the
body, then to working muscles where oxygen is in high demand
• CP supplies are at a low level, so a different source must be used
• Immediate sugar supplies circulating in the blood (blood sugar), as well
as, our sugar storage supplies in the muscle and liver. We refer to our
blood sugar as glucose.
LACTIC ACID SYSTEM
• Pancreas constantly regulates our levels of glucose, when we
accumulate too much in the body stores, the excess in the liver and
muscle. Stored glucose is called glycogen.
• The process of using glycogen or glucose as fuel is called glycolysis
• As the system works without oxygen, and glycogen is the only fuel, the
system of degradation is referred to as anaerobic glycolysis.
• During intense exercise – lactic acid levels rise and continue to rise as
intensity increases
• Lactic acid is produced because insufficient oxygen results in the partial
breakdown of glucose -> provides quick but limited ATP, as well as the
by-product, lactic acid
Examples of activities: 200m, 400m, 800m, 200m freestyle and gymnastic
routines
SOURCES OF FUEL
The only fuel that can be used by the lactic acid system is
carbohydrate. This exists in two forms:
• as glucose in the blood
• in the storage form called glycogen.
Glycogen is broken down, producing ATP and energy for muscular
contraction.
EFFICIENCY OF SYSTEM
The lactic acid system provides ATP quickly, but this requires large quantities of
glucose. In other words, ATP is rapidly available but at considerable cost.
For example, 1 mole of ATP is produced for 180grams of glycogen.
DURATION OF SYSTEM
The duration (work span) of the system depends on the intensity of the activity.
Generally speaking, the lactic acid system produces energy for high
intensity activities lasting from 10 seconds to 1 minute or more depending on the
effort involved. It is the dominant system for all maximal activity performed
between 30 seconds and 2 minutes
For example, 200 metre sprint, 400 metre running, 800 metre running, 200 metre
freestyle and gymnastic routines
CAUSE OF FATIGUE
Fatigue occurs when lactic acid build up within the muscle cells. Although, it is not
directly lactic acid that hinders performance, rather it’s the rate of removal – this
varies on an individual basis.
Lactic acid is produced whenever the body uses carbohydrate as a fuel, and this
occurs most of the time, even at rest. Lactic acid is produced because the
carbohydrate is being metabolised.
The speed of lactic acid production depends on exercise intensity.The faster you
work, the more rapidly lactic acid accumulates.
CAUSE OF FATIGUE
Excessively high levels of lactic acid prevent muscle fibres from contracting and
result in rapid deterioration in performance. However, while lactic acid levels cause
fatigue, tolerable levels can enhance performance because lactate is a fuel source.
Finding a balance and building a tolerance, comes with training, as do removal rates.
WORK SHEET
Relationship between lactic acid and fatigue.
RATE OF RECOVERY
During the post-exercise period, lactic acid diffuses from the muscle
and into the bloodstream where its use as a by-product is important.
In the liver, lactic acid is reconverted to glycogen and can once again
be used as a source of fuel .The process takes about 30 minutes to an
hour.
This further contributes to the body’s efficiency by resynthesising
waste for use at a later stage.
AEROBIC SYSTEM
• Physical activity lasting more than a few minutes requires the presence
of oxygen to ensure the continuation of muscular contraction
• Oxygen is not immediately available at the onset of activity but
becomes gradually available as the oxygen-rich blood fills the muscle
cells.
• This allows the aerobic pathway or oxidative system to become the
predominant supplier of ATP. This process of fuel degradation is
sometimes called aerobic metabolism because oxygen is present. In the
breakdown of glucose and fat (sometimes protein) to produce ATP.
• Lactic acid does not accumulate as oxygen is present.
SOURCES OF FUEL
• Aerobic system can use carbohydrate, fat, even protein as fuel
• During early stages, carbohydrate is the preferred fuel, if exercise
continues beyond an hour or so, fat becomes increasingly important as
a fuel and reigns as the dominant energy source if glycogen supllies
become exhausted
EFFICIENCY OF ATP PRODUCTION
• Lactic acid system is able to generate only 3 moles of ATP from 180
grams of glycogen, the aerobic system is able to generate 39 moles of
ATP from 180g of glycogen.
• Enables us to continue sustained work for longer periods of time
DURATION OF THE SYSTEM
The total amount of glycogen in the body is approximately 350 grams. This is
sufficient for 12 hours of rest or one hour of hard work.
In intermittent exercise, such as football or netball, glycogen supplies last for
approximately four to six hours. However, in the case of marathon runners,
supplies could be exhausted in about two hours.
The body has virtually unlimited supplies of fat and this is used as a fuel
source as glycogen supplies are depleted. In well-trained athletes, the body
mixes carbohydrate and fat in endurance events. This process, called glycogen
sparing, results in some fat fuel being used earlier so that glycogen can be
available at a later stage, such as for a sprint finish. These fuels used jointly, yet
sparingly, ensure that the body can operate using this system for long periods
of time.
DURATION OF THE SYSTEM
The aerobic system is the predominant system for use during extended
endurance events such as marathons and low demand activities such as
walking, sitting and reading.
BUT HOW DOES IT WORK EXACTLY?
Worksheet: Aerobic System
explained
CAUSE OF FATIGUE
The aerobic system is so versatile in fuel usage (remember it can use
carbohydrate, fat and even protein to produce energy), it is not a lack of fuel
but other factors that contribute to fatigue while this system predominates.
During endurance work, slow-twitch muscle fibres will do most of the work.
These fibres have many capillaries and a rich oxygen supply. Before a run,
these fibres may be saturated with glucose. However, activity beyond an hour
or so results in depletion of fuel and, although some is replaced from the liver,
glycogen is exhausted. Glycogen is premium fuel for muscles. When it runs
out, the body tires.
CAUSE OF FATIGUE
A second cause of fatigue is the exhaustion of carbohydrate and subsequent
reliance on the secondary fuel, fat. Although fat is much higher in energy than
carbohydrate, its use as a sole fuel can cause problems. Fatigue occurs because
fat requires more oxygen for metabolism than does carbohydrate. This
increases the runner’s body temperature and rate of respiration.
BY-PRODUCTS OF ENERGY PRODUCTION
During aerobic activity, oxygen is required to burn the fuels in the body
(carbohydrate and fat). As with most fuels that are burnt, by-products are
produced, in this case, carbon dioxide and water.
The carbon dioxide is breathed out through the process of respiration and
the water is available to the cells. These by-products are not harmful to
performance.
RATE OF RECOVERY
The recovery rate of the aerobic system depends on the duration of use. If
used for a short period of time, the system recovers quickly because glycogen
stores have not been depleted. However, if used for hours, glycogen storage
areas could well be exhausted. In this case, it may take days to fully replenish
glycogen reserves.
ENERGY SYSTEMS SUMMARY
The energy systems should not be thought of as individual metabolic units
that operate independently of one another. Although the systems have been
referred to individually, they actually function together (see figure 5.15). This
gives rise to the term predominant energy system, or the system that is being most
utilised at that point in time. This concept is further illustrated in figure 5.15,
where, after 120 seconds of running time, the ATP/PC system is contributing
little to energy supply and the lactic acid system is in decline, although still
assisting to some extent. The contribution of the aerobic system at this point is
predominant and rising gradually.
APPLYING THE ENERGY SYSTEMS
Split into the following groups and work together to complete your assigned task,
groups will need to report back to class with their findings.
Group 1
Group 2
Group 3
 Sham
 Ulia
 Luke
 Ferah
 So’o
 Nahren
 Pisu
 Derek
 Vinnie
 Jerod
 Chantelle
 Katerina
 Jazz
 Billy
 Janita
 Haani
 Vaoesea
 Adrian