2. FOOD FUELS AND THE
ENERGY SYSTEMS
Area of Study 2 - Physiological Responses to Physical
Activity
3. Food Fuels
The food we eat refuels the three energy
systems.
Carbohydrates (CHO)
Pasta
Breads Cerea
l
Carbohydrates are the
preferred source of energy
during exercise as they
require less 02to be broken Fruit &
down. Vegetable
4. Fats
Fats are the body’s main
Oil Fatty meat source of fuel at rest and
during prolonged
submaximal exercise.
Require more 02 than
carbohydrates to be broken
down.
Milk &
cheese
Butter
Nuts
5. Protein
Legumes and grains
Lean
meat
Poultry Eggs
Used mainly for
growth and repair.
Fish
6. Food Types, Fuel Conversions and
Storage
Food Fuel Recommended Food Fuel Storage
Daily Intake (%) following
Digestion
Carbohydrate 55 – 60 Glucose Glycogen –
muscles and liver
Fats (Triglycerides) 25 – 30 Free fatty acids Adipose tissue at
various sites
Protein 10 – 15 Amino acids As muscle at
various sites
7. Energy for Muscle Contraction
Energy for muscular contractions comes from
splitting of a high energy compound called
Adenosine Triphosphate (ATP) which is
stored in very small amounts in the muscles.
Once it is depleted it is quickly replaced by the
three energy systems.
8. ATP Breakdown and Energy
Release
ADENOSI P P P Adenosine
NE Triphosphate
ADENOSI P P P Adenosine Diphosphate
NE
The three energy systems break down fuel stores releasing energy for the resynthesis o
ADENOSI P P P Adenosine
NE Triphosphate
9. Energy Systems
The body has three different ATP producing
systems or pathways:-
ANAEROBIC SYSTEMS (without 02 )
ATP-CP system – also called alactacid, creatine
phosphate or phosphogen system.
Anaerobic Glycolysis – also called lactic acid system
or lactacid system
AEROBIC SYSTEM (with 02 )
AerobicGlycolysis – breakdown of carbohydrates
Anaerobic Lipolysis – breakdown of fats
10. Contribution of Systems to Energy
Production
At rest the demands for ATP are low and an be
met aerobically.
At the onset of exercise the demand for ATP
increases rapidly – as oxygen uptake can’t rise
rapidly enough to meet the demand for ATP
the body calls on the anaerobic systems to
meet the energy shortfall.
It should be noted that all three energy
systems are activated at the start of exercise –
the contribution of each is determined by the
intensity and duration of exercise.
11. ATP – CP System
Chemical fuel – creatine phosphate
No 02 required
Fastest energy production as simple chemical
reactions involved in breakdown
Can supply energy for up to 10secs
Relative ATP production – few; very limited
The more intense the activity the more rapidly CP
stores are depleted
After 5secs of maximal activity CP stores are 50%
depleted and the lactic acid system becomes the
major contributor
13. Creatine Phosphate
Creatine is made:
by the body (from amino acids arginine, glycine and
methionine)
gained from the diet - occurs naturally in meats and
fish
Only 120g of creatine is stored in the body – mainly in the
muscles.
During high intensity exercise, the body allows creatine
phosphate levels to decline in order to use it to
regenerate ATP
Creatine phosphate regenerates during recovery, or
when the exercise intensity is low enough that ATP
demand in the muscles has decreased to the point the
body can use ATP to regenerate creatine phosphate.
14. Creatine Phosphate
CREATINE
PHOSPHATE
Creatine kinase breaks
down creatine phosphate
PHOSPHA
ENERG TE
CREATIN
Y
E
Free creatine can be Free phosphate combines
reformed to creatine with creatine to form
phosphate or released from creatine phosphate or ADP
the cell, processed by the to form ATP.
kidneys and excreted in Energy for this process is
urine. released from the
breakdown of ATP.
15. Anaerobic Glycolysis
Chemical fuel – glycogen (glucose)
02 required – no
Speed of breakdown – fast (chemical reactions
more complex than ATP/CP system
Energy produced – up to 2mins of high intensity
activity – peak usually between 15 and 20
seconds.
Contributes 40-45% of ATP during 100m sprint
Relative ATP production – few; limited (twice as
much as provided by ATP-CP system
By product – lactic acid (disassociates to lactate +
H+.
16. Anaerobic Glycolysis
Repeated high
intensity movements
completed without
rest
e.g. Fast passages
of play in basketball
1km time trial
400m
17. Anaerobic Glycolysis
GLUCOSE
Energy Investment Phase –
two ATP molecules are
GLYCOGEN Glucose 6
invested to prepare
phosphate
molecule to be split
Fructose 6
NAD
bisphosphate
NAD Energy Capture Phase –
NAD NADH four ATPs and two NADH
used to drive the produced per glucose
synthesis NADH NADH molecule
of ATP
2 ATP 2 ATP
LACTATE
PYRUVATE LACTIC
H+
ACID
18.
19. Aerobic System
Chemical fuel/s – glycogen
(carbohydrates), triglyceride (fats), amino acids
(protein)
Preferentially breaks down carbohydrates rather
than fats to release energy – fats produce more
ATP than carbohydrates but have a greater 02
cost (often used during sub-maximal exercise)
02 required – yes
Speed – slow – involves a series of complex
chemical reactions
By products – carbon dioxide/water (non-
fatiguing)
Also activated at the start of onset of intense
exercise – 02 uptake can be as high as 90% in 30-
20. Aerobic System
Cycling
(distance)
Running
(distance)
Triathlon
21. Aerobic Glycolysis
GLYCOGEN
GLUCOSE ATP
Aerobic Glycolysis – in
Energy
the for
Energ 2 -3
presence of 02 pyruvate y muscle
PYRUVATE ATPS contractio
is is converted to acetyl
n
coenzyme A, the entry
molecule for the Krebs
O2
ATP+ Pi
cycle.
ACETYL
COENZYME A
ATP
Energ
y
Energy
KREBS CYCLE 36 for
muscle
ATPS contractio
Energ n
y
ELECTRON ATP+ Pi
TRANSPORT
CHAIN
22. Aerobic Lipolysis
FATS
Lipolysis – metabolic breakdown of
triglycerides into free fatty acids
and glycerol in muscle cells.
GLYCEROL &
FREE FATTY
ACIDS Beta oxidation – is the process by
fatty acids are broken down in the
mitochondria to generate acetyl
coenzyme A, the entry molecule for
ACETYL the Krebs cycle.
COENZYME A
ATP
KREBS CYCLE Energ
y
Energy
for
147 muscle
ATPS contractio
Energ n
ELECTRON
y
TRANSPORT
SYSTEM ATP+ Pi
23. Krebs Cycle (Citric Acid Cycle)
The Krebs cycle is a complex series of
chemical reactions that continues the
oxidization of glucose and fats. Acetyl
coenzyme A enters the Krebs cycle and is
broken down in to carbon dioxide and
hydrogen allowing more two more ATPs to be
formed.
Hydrogen combines with two enzymes called
NAD (forms NADH) and FAD (forms FADH2)
both of which are high energy
compounds, and is transported to the Electron
Transport Chain.
26. Electron Transport Chain
Hydrogen is carried to the electron transport
chain, another series of chemical
reactions, and here it combines with oxygen to
form water thus preventing acidification. This
chain, which requires the presence of
oxygen, also produces heat and results in 34
ATPs being formed.
