Aerobic and Anaerobic
Pathways- An
Introduction to Energy
Systems
YEAR 11 PE
Chapter Overview
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ATP (adenosine triphosphate) is used for muscle
contraction. This is stored in muscles (in small amounts)
and can be converted from food fuel sources.
During exercise, ATP is broken down to adenosine
diphosphate (ADP) and phosphate molecule.
As ATP stores as depleted, resynthesis occurs to convert
ADP back to ATP.
3 energy systems:
 ATP-PC system (No O² required)
 Anaerobic glycolysis- Lactic acid system (No O² required)
 Aerobic system (O² required)
ATP for energy use
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Food is our primary energy source.
These sources include carbohydrates, fats and protein.
Our main fuel source is carbohydrates, with protein used
very sparingly.
Foods and their Conversion to
Energy
Immediately available, quickest source of energy
(PC)
 Does not require O²
 Dominant energy system for first 1-5 secs of
exercise, peak power between 2-4 secs
 Depleted after 10 secs of exercise
 Once PC has been depleted, 50 per cent
replenishment is achieved within 30 seconds of
passive recovery, total replenishment takes 3+
minutes.
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ATP-PC SYSTEM
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Used for high-intensity activities involving
explosive movements such as sprinting, long
jumping and throwing the javelin.
Linked to the fitness components of muscular
power and speed.
PC is not used for muscle contraction, it is mainly
used for resynthesising ATP. ATP is broken down
to adenosine diphosphate (ADP). As rapidly as
this breakdown occurs, the remaining PC is
broken down to join with the ADP to form ATP
again. This is the resynthesising process of ATP.
ATP-PC SYSTEM
ATP-PC SYSTEM
1.
What is the body’s primary source of
energy?
1.
Why do we call upon the ATP-PC system
at the start at exercise?
Check Your Understanding
Glycogen is broken down to form ATP.
Lactic acid is produced as a by-product to energy
release
 Does not require O²
 Predominant energy system for activity lasting
10-75 secs, peak power occurs between 5-15
secs.
 Used for activity including 100-metre freestyle
swimming at the elite level, or gymnastics
routines.
 Linked to the fitness components of muscular
power and speed.
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ANAEROBIC GLYCOLYSIS
ANAEROBIC GLYCOLYSIS
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Requires O²
Glycogen is broken down to form ATP without
producing any by-products.
At rest or during extended endurance
activity, aerobic system uses fats. Fats can
produce more ATP than carbohydrates, but
they require more oxygen to produce the
equivalent amount of ATP.
Peak power occurs between 1 and 2 minutes.
Dominant system for activities that are more
than 75 seconds in total duration.
AEROBIC SYSTEM
3 stages in aerobic energy production
 Stage 1 – the breakdown of carbohydrates and
fats to produce 2 ATP molecules
 Stage 2 – Kreb’s cycle, which involves the
breakdown of pyruvic acid into carbon dioxide.
Further energy is released to resynthesise to ATP
for a net production of 1 ATP molecule.
 Stage 3 – the electron transport stage, which
involves water, heat and produces the largest
yield of ATP – a total of 34 molecules
AEROBIC SYSTEM
ANAEROBIC VS AEROBIC
The 3
energy
systems
Fuel
Oxygen?
Max ATP
produced
(moles)
Peak
power in
Max effort
Typical
events
100m
jumps
throws
hitting
ByRecovery
Intensity
products
time
Small amount of
stored ATP
Phosphocreatine
(PC) - broken
down to make
more ATP
NO
0.7
2-4 sec
Lactic Acid Glycogen - from
System
Carbohydrates
NO
1.2
5-15 sec
200400m
lactic acid
50m swim
YES
98 (38per
mole of
glycogen)
1-2 min
marathon
cycling
archery
ATP-PC
System
Aerobic
System
Carbohydrates
Fats
3 ENERGY SYSTEMS
nil
H20
CO2
Heat
95-100%
50% in
30sec
100% in
3 min
85-100%
20min - 2
hr
60-85%
up to 25days
1.
What is the by-product produced by
anaerobic glycolysis?
2.
How do the aerobic and anaerobic
systems differ?
Check Your Understanding
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All three energy systems are activated at the
start of exercise and no single system works by
itself.
ENERGY SYSTEM INTERPLAY
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All 3 systems begin to produce energy at the start of the event.
The ATP-PC system contributes by far the most ATP (energy) in
the first 5 seconds, after this time the PC is depleted to about
50%
The Lactic Acid system is at its peak between 5-15 seconds so it
becomes the major contributor as the ATP-PC system slows down
from 5 seconds.
The ATP-PC system continues to supply ATP until fully depleted
after around 10-15 seconds.
The Lactic Acid system continues to be the major contributor until
around 30 seconds when the Aerobic system has had time to
begin to supply more ATP. The Lactic Acid system begins to slow
down after 30 seconds as the Aerobic system takes over more.
The Lactic Acid system continues to supply some ATP for the
duration – but has slowed down to avoid fatigue caused by
excessive Lactic Acid accumulation.
The Lactic Acid system supplies the most ATP for this event.
400m Race example
Choose either shotput, 100m or 800m
event
 In regards to this event, explain the
contribution of each energy system.
 Explain the interplay relationship between
the energy systems
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eg. 400m race
Check Your Understanding