ENERGY SYSTEMS
•
LESSON 6
Factors Affecting the Energy
System used
LEARNING OBJECTIVES
1.
Can I explain the factors affecting the
energy system used?
STARTER
STARTER ANSWER
 The
bus is headed to the right,
otherwise we would see the
entrance door!
FACTORS AFFECTING THE
ENERGY SYSTEM USED

Explain how the following affects the energy
system used by athletes:
Exercise Intensity and Duration
 Energy System Threshold
 O2 Transport/Supply
 Food/Fuel available
 Enzyme Activation Levels
 Fitness Level

EXERCISE INTENSITY AND
DURATION

A combination of exercise intensity and duration
can determine the predominant energy system(s)
being used. When exercise intensity is anaerobic
(high intensity, short duration), then the
ATP/PC and LA Systems will be predominant.
If the exercise intensity is aerobic (medium/low
intensity, long duration), then the Aerobic
System will be predominant.
EXERCISE INTENSITY AND
DURATION

When the aerobic system cannot supply energy quick
enough, it has to use the LA system to continue to
provide energy for re-synthesis of ATP. During high
intensities lactate production will start to accumulate
above resting levels. This is termed Lactate
Threshold. When blood lactate levels reach 4mmol/L
(normal resting levels are 1-2mmol/L), the exercise
intensity is referred to as ‘the Onset of Blood Lactate
Accumulation’ (OBLA). OBLA continues to increase
if exercise intensity is maintained or increased and will
cause muscle fatigue.
EXERCISE INTENSITY AND
DURATION
 After
training the intensity level for
lactate threshold is increased and this
will delay the point at which OBLA is
reached and therefore increases the
potential duration/threshold of the LA
energy System.
ENERGY SYSTEM
THRESHOLD

The Threshold for any system is ‘the point at
which that energy system is unable to
provide energy.’ Or ‘the point at which one
energy system is taken over by another as
the predominant energy system to provide
energy for ATP re-synthesis.’
ENERGY SYSTEM THRESHOLD
Performance
Duration
Less than 10
seconds
10-90 seconds
90 secs – 3 mins
3+ mins
Energy
System(s)
Involved
(predominant in
bold)
ATP/PC
ATP/PC
LA
LA
Aerobic
Aerobic
Practical Example
Triple Jump/100m
sprint
200-400m sprint
100m swin
Boxing (3 min
rounds)
800/1500m
Low impact aerobics
class
Marathon
ENERGY SYSTEM
THRESHOLD

The energy system threshold alters in response to a
combination of both intensity and duration of
exercise and will not always go through each energy
system in turn. For example, a cyclist cycling at a
low intensity will be using the Aerobic System,
although when going up hill they may exceed the
intensity threshold of the aerobic system and the
lactic acid system will take over as the predominant
energy system. In team games, players will switch
between the three energy systems.
O2 TRANSPORT/SUPPLY

If there is O2 present then the aerobic
system can provide energy to re-synthesise
ATP. If O2 supplies falls below that
demanded by the exercise then the aerobic
system threshold is met and the lactic acid
system will start to break down glucose
anaerobically.
FOOD/FUEL AVAILABLE

If the body has sufficient stores of PC, it is able to use
the ATP/PC system for very high intensity, short
duration activity/movements. PC stores are limited, but
are available at the start and after recovery during
exercise. If exercise starts too high then PC stores will
quickly deplete and exercise at that intensity cannot be
sustained. PC stores can be conserved by pacing and resynthesising PC stores during recovery periods using
spare energy from the aerobic system.
FOOD/FUEL AVAILABLE

Glycogen is the major fuel for the first 20
minutes of exercise. This is due to O2
supplies being limited as it takes 2-3
minutes for the cardiovascular system to
supply sufficient O2. As well as glycogen
being readily available in the muscles,
requires less O2 and is easier to break
down than FFA’s
FOOD/FUEL AVAILABLE

After about 20-45 minutes there is a
greater breakdown of fats alongside
glycogen as the energy fuel. FFA’s are a
more efficient fuel than glycogen, but
require 15% more O2. If a performer has
larger muscle/liver glycogen store, then
they can perform work aerobically at a
higher intensity.
FOOD/FUEL AVAILABLE

Glycogen stores become nearly depleted after
about two hours, then FFA’s have to be used for
aerobic energy production, and unless exercise
intensity is reduced it can bring on the sudden
onset of fatigue (‘hitting the wall’). Once OBLA
is reached the body has insufficient O2 available
to burn FFA’s and will then have to break down
glycogen ‘anaerobically’ to re-synthesise ATP
ENZYME ACTIVATION LEVELS
Factors Affecting Enzyme Activation for the
Energy Systems
Activating Factor
Releases
Controlling
Enzyme(s)
Activating Energy
System
Increase in ADP;
decrease in ATP
Creatine Kinase
PC
Decrease in PC
PFK
LA System
Increase in
adrenalin; decrease
in insulin
PFK
Aerobic System
FITNESS LEVEL

The more aerobically fit the performer, the more
efficient their cardiovascular and respiratory
systems are. Aerobic athletes have also shown
that they can start to use FFA’s earlier during
sub-maximal exercise, which conserves glycogen
stores. The overall effect is that the aerobic
threshold in terms of intensity and duration can
be increased as the lactate threshold/OBLA
would be delayed.
FITNESS LEVEL

A typical untrained athlete would reach OBLA
at about 50-56% of their VO2 max, whereas an
aerobic-trained athlete would not reach OBLA
until about 85-90% of their VO2 max.


An anaerobic-trained athlete will increase their
ATP/PC, glycogen stores, anaerobic enzymes
and tolerance to lactic acid. All of this would
increase the threshold of both ATP/PC and
Lactic Acid Systems.
PLENARY
Summarise
the factors that
affect the energy system
used