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ENERGY SYSTEMS
What you need to know…
• ATP-PC, Lactic Acid, Aerobic systems
– Key points, how they work
• Summary of the three energy systems
• Energy systems interplay
The Three Energy Systems
• There are three pathways or energy
systems responsible for the resynthesis
(___________) of ATP and supply of
energy
• Which of the three energy systems
operates during exercise depends on:
– ___________ of exercise
– How urgently the energy is required
– ___________ of exercise
– Whether or not ___________ is present
The Three Energy Systems
• The energy for muscular contractions is
produced either anaerobically or
aerobically via three energy systems
– Anaerobic systems
1. ATP-PC system
2. Lactic Acid system
– Aerobic system
3. Aerobic system
The Three Energy Systems
• The three energy systems do not function
independently or one at a time; all three energy
systems are activated at the start of exercise
and their relative contribution is determined by
intensity and duration of exercise
• At rest, our demands for ATP are ___________
and can be met ___________
• As we start to exercise, the demand for ATP
___________ rapidly, especially during maximal
activities and the ATP demands are met
___________
• However, if the exercise is less intense and
longer ATP demands can be mostly met
aerobically
Energy for Rest and Activity
•
The body can create energy (ATP) under two
main conditions
1. Rest: where there is enough (sufficient)
oxygen available for the body to continue to
function at a resting level
2. Activity: where physical exertion means
there is not enough (insufficient) oxygen
available for the body to continue to function
at a particular level without a large increase
in oxygen intake
At Rest
• The body has lots of oxygen available
• 2/3 energy comes from ___________
– More ___________ is contained in fat than
carbohydrate
• 1/3 energy comes from ___________
• The end products of aerobic metabolism
are:
– Carbon dioxide (CO2), water (H2O) and heat
During Activity
• Increased oxygen supply needed to go to
working ___________
• Exercise of short duration and high
intensity the ___________ systems
supply most of the required energy
– Carbohydrate main fuel
• Exercise of longer duration and low
intensity ___________ system supplies
energy
– Carbohydrate initial fuel, then fat main fuel
once CHO is used
ATP-PC System
• Also known as: phosphate, PC, CP,
phosphocreatine systems
• It’s an anaerobic system = no oxygen
• A small amount of ___________ is
stored in the muscles
• Primary system for maximal intensity
efforts of 1-10 seconds duration
– Eg:
ATP-PC System
How it works
• Once ATP (stored in muscles) is used ATP
needs to be ___________
• As we learnt earlier ATP is reformed using ADP
and a free phosphate molecule (Pi)
• This process requires energy
– Phosphocreatine (PC) is the chemical compound
that provides this energy
– There is ~4 times the amount of PC in muscles than
ATP
• So, PC is broken down to create energy and
this energy is used to reform ATP from ADP
– PC releases a free phosphate:
– PC = P + C
– ADP + P = ATP
ATP-PC System
Summary
• Provides most rapidly available source of ATP
for energy because it depends on short and
simple chemical reactions
• Anaerobic system so it doesn’t rely on
___________ to release energy
• ATP & PC both stored in ___________ and
available for immediate energy release
• Although, after 5 seconds ~50% is depleted
• Once PC is completely used, ATP must be
reformed in other ways
– Usually via glycogen (stored in muscles and liver)
using anaerobic glycolysis from the lactic acid system
Lactic Acid System
• Also know as: anaerobic glycolysis,
lactacid systems
• It’s an anaerobic system = no oxygen
• Provides bulk of ATP production for high
intensity, sub-maximal efforts
– Eg:
• Duration: 10 sec – 2-3 mins
• Intensity: 85 – 95% max HR
Lactic Acid System
How it works
• As we know, there is not enough PC in the
muscles to continuously repair ADP  ATP
• In the lactic acid system this resynthesis of ATP
is done differently
• This energy comes from the breakdown of
___________ (process is known as glycolysis)
• Because oxygen is not present the glycogen is
not totally broken down
– Pyruvic acid is created and because there is no oxygen it
is converted to lactic acid
– Hydrogen ions also released
– See figure 2.10, p.69
• As by-products (lactic acid and hydrogen ions)
increase in the muscles it decreases the rate of
ATP rebuilding and leads to ___________
Lactic Acid System
Summary
• Requires no oxygen
• More complex reactions than the
ATP-PC system to release energy
• Requires glycogen to be broken
down to release energy (glycolysis)
• Produces lactic acid, which
contributes to fatigue
• Is the system used for sub-maximal
activities when the PC is depleted
until the aerobic system can be used
Aerobic System
• Also known as: aerobic glycolysis, oxygen
systems
• Creates the most energy out of all three
systems
• Is the ___________ at creating energy
• Contributes majority of ATP production in submaximal, longer efforts
– Eg:
• Duration: >30 sec
• Intensity: <85% max HR
Aerobic System
How it works
• Stage 1: Carbohydrates (glycogen) is broken
down into glucose and pyruvic acid using
oxygen (aerobic glycolysis)
– Occurs in the mitochondria (aerobic powerhouse)
– See figure 2.11, p.70
• Because oxygen is present a more complete
breakdown of glycogen occurs resulting in no
lactic acid
• Stage 2: Instead of pyruvic acid becoming lactic
acid it is further broken down in the citric acid
cycle (Kreb’s cycle), releasing ___________
and CO2
• Stage 3: The electron transport chain also
produces large amounts of ATP along with
___________ and ___________
– See figure 2.12, p.71
Aerobic System
Summary
• Requires oxygen
• Dominant system for sub-maximal activities
• Many more complex reactions than the ATP-PC
& lactic acid systems
• Prefers to break down CHO rather than fats
– Although ___________ can produce more ATP
– However, fats require more oxygen to produce the
same amount of ATP as CHO
• Releases no toxic by-products and can be used
indefinitely
• Produces far more ATP than the anaerobic
systems
• However, still contributes significant amounts of
energy during high intensity efforts lasting 1-2
minutes
Comparing the Three Energy Systems
• Complete the summary table
ATP (Energy) Production
• The ___________ and ___________ of
the physical activity determine which of
the energy systems is the dominant
contributor to ATP (energy) production
• See figure 2.14, p.74 and figures 2.15 &
2.16, p.75
Energy System Interplay
• Virtually all physical activities receive
energy from each of the three energy
systems
• Each system is best suited to supplying
energy for specific types of events or
activities
• They overlap each other depending on
the type of activity and exercise
demands
• They do not turn themselves on and off
REVISION QUESTIONS
1/ The ATP-PC system is the quickest to supply energy because it:
A
has an indefinite supply of stored ATP
B
does not use oxygen
C
is immediately available, is the simplest and quickest system
for breaking down PC to create ATP, and is stored in muscle cells
D
is more powerful than fats
2/ Marcus runs a 100m heat at his school athletics carnival,
qualifying for the final in 12 secs. Most of the PC depleted during
the 100m will be resynthesised during:
A
the first 3 minutes of an active recovery
B
1 minute of active recovery and eating high GI food
C
30 seconds
D
the first part of EPOC
REVISION QUESTIONS
3/ Discuss the energy system contribution for a 200m swimming
event lasting 1 minute 45 seconds.
4/ What are triglycerides? (2 marks)
5/ What are they broken down to? (1 mark)
6/ Why and when would a recreational marathon runner possibly
rely on fat as a fuel? (2 marks)