Energy Systems
©Subject Support 2010.
Learning Objectives
 To understand the different energy
systems
 To understand each energy systems use
in sport and exercise
REMEMBER
Energy can be defined as the capacity to
do work!
Grading Criteria
 P7 – Describe the three different energy
systems and their use in sport and exercise
activities
 M4 – Explain the three different energy
systems and their use in sport and exercise
activities
 D2 – Analyse the three different energy
systems and their use in sport and exercise
activities
Unit Content
 Energy systems – Phosphocreatine; Lactic
Acid; Aerobic energy system
 Amount of ATP produced by each systems
 Sports that use these systems to provide
energy
 Recovery time
Energy Systems
• ATP-PC System
(anaerobic)
• Lactic Acid System
(anaerobic)
• Aerobic Energy System
©Subject Support 2010.
Energy Systems
The use of each system depends on the intensity and
duration of each activity:
 If the activity is short in duration (less than 10
seconds) and high intensity, we use the ATP-PC
system
 If the activity is longer than 10 seconds and up to 3
minutes at high intensity, we use the lactic acid
system
 If the activity is long in duration and submaximal
pace, we use the aerobic system
Energy Continuum
Sometimes we need to use all three systems to
regenerate ATP because the demands of an activity are
varied. For example, in rugby:
 A short sprint to tackle a player uses the ATP-PC
system
 A long sprint the length of the pitch to score a try
uses the lactic acid system
 Positional play will use the anaerobic system
Adenosine Triphosphate (ATP)
 ATP is vital for muscle contraction it is the only
form of useable energy in the body
 The body only has enough ATP stored for 1
explosive act (about 3 seconds)
 After that there is none left
 Then energy has to be created by other means
ATP (1 explosive act) = ADP (adenosine
phosphate)
ATP – Adenosine TriPhosphate
ADENOSINE
PHOSPHATE
High
energy
bond
PHOSPHATE
PHOSPHATE
ADP – Adenosine DiPhosphate
ADENOSINE
PHOSPHATE
PHOSPHATE
ENERGY
PHOSPHATE
Phosphocreatine Energy System (ATP/PCr
System)
ADP + Creatine Phosphate (PCr) = ATP
 Lasts about 10 seconds
 High intensity maximum work
 Extremely efficient
 Does not need oxygen
 Has no waste products
Think 100 meters
 Advantages
ATP-PC System

Phosphocreatine stores can be regenerated quickly (50%
replenishment in 30 s; 100% in
3 mins)

No fatiguing by-products

Creatine supplementation extends the time that the ATP–PC system
can be utilised
 Disadvantages

There is a limited supply of phosphocreatine in the muscle cells, i.e.
it can only last for 10 s

Only 1 molecule of ATP can be regenerated for every molecule of PC

PC regeneration can only take place in the presence of oxygen (i.e.
when the intensity of the exercise is reduced)
Lactic Acid Energy System
ADP + Glucose = ATP
 When PCr runs out, the muscles call upon
stores of glucose (glycogen).
 Lasts between 10-60 seconds.
 Has a waste product called pyruvic acid
 If not enough oxygen is breathed in to break
pyruvic acid down (oxygen debt) it converts
into lactic acid
 This is also called anaerobic glycolysis
Think 400m
Lactic Acid Energy System
Glycogen in Liver
Carbohydrate in
Food
Glucose in
bloodstream
Muscle
Sarcoplasm
ANAEROBIC
Glucose in Muscle
2 ATP
Glycolysis
Pyruvic Acid
Lactic Acid (1)
+ O2
Acetyl Coenzyme A
Lactic Acid (1)
Lactic Acid System
Advantages
ATP can be regenerated quite quickly because few chemical
reactions are involved.
In the presence of oxygen, lactic acid can be converted back
into liver glycogen, or used as a fuel by oxidation into carbon
dioxide and water.
It can be used for a sprint finish (i.e. to produce an extra
burst of energy).
Lactic Acid System
Disadvantages
Lactic acid is the by-product! The accumulation of acid
in the body denatures enzymes and prevents them
increasing the rate at which chemical reactions take
place.
Only a small amount of energy (5%) can be released
from glycogen under anaerobic conditions (as opposed
to 95% under aerobic conditions).
Aerobic Energy System
 Starts similar to the Lactic Acid system
ADP + P + Glucose = ATP + Pyruvic Acid
 As oxygen is present the pyruvic acid does
not convert into lactic acid but into another
34 molecules of ATP
 Long term low intensity exercise
 Carbon dioxide (CO2) and water (H2O0 are
waste products of this system
Think long distance running
Aerobic Energy System
O2
 The aerobic system of energy production needs
oxygen.
 Breaks down carbohydrates & fats into CO2, H20 and
ENERGY
 Takes approx 3 mins to extract 95% of energy from
glucose molecule
 This supplies the body with a prolonged and steady
supply of energy.
Aerobic Energy System
 Immediate energy production, therefore comes
from the other two anaerobic systems used.
 Heart rate and ventilation rate increase during
exercise. The vascular system distributes more
oxygenated blood to our working muscles.
 Within 1-2 mins the muscles are being supplied
with enough oxygen to allow effective aerobic
respiration
ATP (1 burst of energy) =ADP
ADP+ PCr = ATP (3-10s of work) = ADP
ADP + Glucose= ATP (10-60s of work)
= ADP + Pyruvic Acid
(No oxygen = lactic acid)
ADP + P + Glucose = ADP + Pyruvic Acid
+ Oxygen =34 ATP + CO2 + H20
ANAEROBIC
Muscle Sarcoplasm
Pyruvic Acid
Acetyl CoA
Muscle
Mitochondria
O2
AEROBIC
2 ATP
Glycolysis
+ Oxaloacetic Acid
2 ATP
Citric
Acid
Krebs
Cycle
Hydrogen
Electron Transport Chain
Carbon
Dioxide
Electron Transport
Chain
The Aerobic System
Advantages
 More ATP can be produced — 38 ATP from the complete
breakdown of one glucose molecule.
 There are no fatiguing by-products (only carbon dioxide
and water).
 Stores of of glycogen and triglyceride are plentiful, so
exercise can last for a long time.
The Aerobic System
Disadvantages

This is a complicated system so it cannot be used
immediately. It takes time for enough oxygen to become
available to meet the demands of the activity and ensure
glycogen and fatty acids are completely broken down.

Fatty acid transportation to muscles is low and fatty acids
require 15% more oxygen to break them down than
glycogen.
Food Fuels
 Food is the basic form of energy for ATP regeneration. The
main energy foods are:
 carbohydrates — stored as glycogen and converted into
glucose during exercise
 glycogen — a complex sugar supplied from muscle or
liver stores
 glucose — a simple sugar supplied from the blood
 fats — stored as triglycerides in adipose tissue under the
skin and converted by the enzyme lipase to free fatty
acids when required
When are These Fuels Used During Exercise?

The intensity and duration of exercise play a
huge a role in determining whether fats or carbohydrates
are used.

The breakdown of fats to free fatty acids requires more
oxygen than that required to breakdown glycogen. It is
also a much slower process.

Therefore, during high-intensity exercise when oxygen is
in limited supply, glycogen will be the preferred source of
energy.