1. Energy Systems
Muscle Contraction
ATP

2. Foods consumed to Produce
Energy
Food Consumed
Digestion
Absorption into blood
transported to
Active cells
Immediate usage
or storage
Carbohydrate
Glucose
Energy
Pathways
to ATP
Storage
As
glycogen
ATP
Fat
Fatty Acids
Energy
Pathways
To ATP
Storage
As adipose
tissue
Protein
Amino Acids
Energy
Pathways
To ATP
Storage
& repair
of tissue

3. The muscles of the body use both carbohydrates and fats to produce
energy. The following diagram shows how carbohydrates are used.
Making Energy Available to the Cells of the Body
 Carbohydrates in the form of starch gained from foods such as
pasta, bread and potatoes are eaten.
 The starch is digested in the gut and turned into glucose molecules.
 The glucose enters the small intestine where it passes into
the blood.

4. The glucose is then used in 3 different
ways…
Here some of the
glucose is stored
as glycogen and
used to maintain
blood sugar levels.
Glucose is stored here
as glycogen and is used
when the body is
working harder.
Glucose diffuses
easily into the
cells and is used
to meet their
energy demands.
Skeletal Muscle
LiverBody Cells

5. The ATP
Cycle
• Energy is released in the body by the breakdown of
carbohydrates, fats and proteins to produce adenosine
triphosphate or ATP.
• ATP consists of a substance called adenosine and three
phosphate groups.
• Special high-energy bonds exist between the phosphate
groups.
• Breaking one of the phosphate bonds releases energy. In
a muscle cell, the breakdown of ATP results in
mechanical work (muscle contraction) and heat.
• When ATP loses one of its phosphate bonds, energy is
produced and it is converted to ADP (adenosine
diphosphate).
• Once this has occurred ADP is resynthesised back into
ATP by a process called 'coupled reactions' which is a bit
like a shuttle system.
Click here to see a demonstration of ATP

6. ATP & Exercise
• ATP can be resynthesised in three different ways and
these are referred to as the ‘energy systems’.
• The first two energy systems (phosphcreatine & lactic
acid) are termed ‘anaerobic’ because ATP is produced
very quickly without oxygen.
• The third energy system, ‘aerobic’, produces ATP
slowly with oxygen.

7. ATP-PC System (anaerobic)
• Creatine Phosphate is found in our muscles and stored in
limited amounts. When added to ADP, will remake ATP.
• The ATP-PC system is used when an activity lasts between
6 and 10 seconds, such as short sprints in some sports,
lifting weights and some gymnastic events such as vaulting
• After 6-10 Seconds, Creatine Phosphate must be
regenerated, so other fuels eg glycogen and fats, must
supply energy for the regeneration of ATP.

8. Lactic Acid System (anaerobic)
• The Lactic acid system uses glycogen in the absence of oxygen to make
ATP.
• ADP and glycogen (made from carbohydrates) are combined to make more
ATP.
• Without oxygen, glucose can produce a little ATP, known as ANAEROBIC
GLYCOLYSIS but these stores deplete very quickly.
• During glycolysis, glycogen produces by products called pyruvate and
hydrogen ions. These compounds together form Lactic acid.

9. Lactic Acid System (anaerobic)
• If the rate of lactic acid production exceeds the rate of removal, muscles
become tired and muscle contraction is impeded.
• To avoid fatigue, exercise intensity must be reduced so that the lactic acid
can be carried away from the muscles by the bloodstream to the liver, for
conversion back into glucose or used by other cells receiving a sufficient
supply of oxygen.
• Type 2a fibres are well adapted to carrying fast rates of glycolysis, but
cannot tolerate high levels of lactate. Suitable activities are 400m, & sports
that have repeated sprints, eg football, rugby or high energy activities
• Lasts for up to 90 seconds

10. Glucose Produces…

11. Glucose produces…
Lactic acid quickly
builds up & makes
the muscles feel
tired & painful. ‘All
out effort’ cannot
last for very long!
Some is used for
muscle contractions,
creating movement.

12. Glucose produces…
Lactic acid quickly
builds up & makes
the muscles feel
tired & painful. ‘All
out effort’ cannot
last for very long!
The rest is
converted into heat
to warm the body.
Some is used for
muscle contractions,
creating movement.

13. Aerobic System (aerobic!)
• The aerobic production of ATP takes place in the presence of oxygen using a
mixture of fatty acids and glucose as fuel. This is very efficient at producing energy.
• This process occurs within specialised structures in the muscle cell, called
mitochondria, that contain special enzymes needed by the cell to use oxygen.
• The by product of this system is Carbon Dioxide and Water.
• A key adaptation to regular aerobic training is the body becomes more efficient in
mobilising, transporting and oxidising fatty acids. This is because the body
develops a greater number of mitochondria and fat oxidising enzymes. So the
body becomes more efficient at burning body fat.
• This is important for endurance activities, because glycogen is in much shorter
supply than fat. By using more fatty acids you can make your glycogen stores last
much longer

14. Glucose and
oxygen produce…

15. Aerobic respiration is how marathon runners produce the energy that
is used in long periods of less intensive effort.
Glucose and
oxygen produce…
Some is used for
muscle contractions,
creating movement.

16. Aerobic respiration is how marathon runners produce the energy that
is used in long periods of less intensive effort.
Glucose and
oxygen produce…
Carbon dioxide,
which is carried
away by the blood
& excreted through
the lungs.
Water, which is
carried away by the
blood and excreted
through the lungs,
sweat and urine.
Some is used for
muscle contractions,
creating movement.
The rest is converted
into heat to warm
the body.

17. Summary Table
Energy System Fuel Used Rate of ATP
Production
Capacity of
Energy
System
Main Use
Phosophocreatine Creatine Phosphate
(stored in the muscle)
Very rapid Very limited ATP
production
Very high intensity
short duration
activities of 1-
10 seconds
Lactic Acid Glycogen
(stored in the muscle
and liver)
Rapid
By-product is
lactic acid
which can
lead to
muscular
fatigue
Limited ATP
production
High intensity
short duration
activities of 20
secs – 90 secs
Aerobic Glycogen
Fatty Acids (stored in
the adipose
tissue)
Slow
By-products are
carbon-
dioxide and
water
Unlimited ATP
production
Moderate to
vigorous
intensity
activites, long
duration 3
mins +
The higher the exercise intensity, the more dependant you are upon glycogen.
The type of fuel you use depends upon exercise duration, intensity and type.

18. Energy Systems and Special
Populations
•Children have more mitochondria in their muscles and
are therefore more able to use oxygen more efficiently.
•They have a high anaerobic threshold, so as long as
they are working at an appropriate intensity, they are
able to keep going.
•But they have limited supplies of muscle and liver
glycogen, smaller anaerobic fuel stores and the capacity
to use it. So they are not able to tolerate short bursts of
energy ot exercises that require high intensity and short
reps.
•This does improve with age

19. Energy Systems and Special
Populations
•There is a gradual increase in energy expenditure
as pregnancy advances.
•Pregnant exercisers use more carbohydrates than
fat during moderate exercise. Therefore, blood
sugar levels can fall quickly.
•It should be noted that blood glucose can be
reduced after strenuous exercise especially in the
latter stages of pregnancy

20. Energy Systems and Special
Populations
The ability of skeletal muscle to produce energy
becomes less efficient with age.
Levels of ATP and creatine phosphate decline
with activity in older people. This means that
they may be less able to regenerate ATP.
Also the enzymes responsible for energy
release reduce in concentration and
effectiveness.
This can lead to reduced energy production