This document discusses the different fuel sources and energy systems used during exercise. Carbohydrates are the primary energy source and are broken down into glucose. Fat is also an important fuel during prolonged, less intense exercise. Protein is a minor fuel source used during starvation or severe depletion of other fuels. There are three energy systems: immediate uses ATP and phosphocreatine and lasts up to 15 seconds; short term uses anaerobic glycolysis to break down glycogen for 1-2 minutes; long term is the oxidative system and is the primary fuel for endurance events using fat and carbohydrate oxidation. The different systems contribute varying amounts depending on the duration and intensity of the exercise.

1. Fuel for Exercising
Muscle

2. Fuel for Energy
Energy
Source
Carbohydrate
Fat
Protein

3. Carbohydrate
Primary source of energy
All carbohydrate is ultimately broken down to
glucose or stored in the muscle or liver as glycogen
Dietary sources of starches and sugar to replenish
carbohydrate reserve.

4. FAT
Large source of energy during prolonged, less
intense exercise.
Rate of energy release is slow.
Less readily available for cellular metabolism because
it must be reduced from its complex form.

5. Protein
Minor energy source
Utilized during severe depletion of the other
macronutrients or during starvation.
It can be used to generate free fatty acids FFAs for cellular
energy
Or converted to glucose through the process of
gluconeogenesis.
It can supply 5 to 10% of the energy needed to sustain
prolonged exercise.

6. Rate of Energy Release

7. Bioenergetics
Phosphorylation
Anaerobic metabolism
Aerobic metabolism

8. Fuel for Energy
Three Energy Systems
Immediate (ATP – Phosphocreatine System)
Short Term (Glycolytic System)
Long Term (Oxidative System)

9. ATP – PCr System
Simplest of the energy systems.
This process does not require oxygen, but it can occur in
the presence of oxygen.
During the first few seconds of intense muscular activity
(sprinting), adenosine triphosphate (ATP) is maintained at
a relatively constant level as phosphocreatine (PCr)
declines.
Combination of ATP and PCr stores can sustain the
muscles energy needs for up to approximately 15 sec of an
all out sprint.

10. Short term system
Liberation of energy through the breakdown of
glucose.
Anaerobic glycolysis entails a complex process
involving 10 – 12 enzymatic reactions for the
breakdown of glycogen to lactic acid.
Does not produce large amount of ATP.
Predominates during early minutes of high intense
exercise (all out sprint for 1 – 2 min).

13. Long Term System
Most complex of the three system
Slow to turn on, but has a tremendous energy –
yielding capacity
Primary method of energy production during
endurance events.

17. Oxidation of Fat
Triglycerides - major
energy source
Lipolysis carried out by
lipases
Beta Oxidation – Enzymatic
catabolism of fat by the
mitochondria.
FFA is cleaved to acetic acid

18. Oxidation of Protein
Gluconeogenesis
Conversion into intermediates (pyruvate / acetyl
CoA)
Energy yielded approx. 4.1 kcal/g

19. Interaction of the three
energy systems
Do not work independent of each other.
Each system contributes to the total energy needs of
the body.
One system usually predominates, depending on the
activity.

20. Running Event Immediate Short Term Long Term
100 m 95 3 2
200 m 95 2 3
400 m 80 15 5
800 m 30 65 5
1,500 m 20 55 25
3,000 m 20 40 40
5,000 m 10 20 70
10,000 m 5 15 80
Marathon (42.2
km)
5 5 90
Percentage of Emphasis on the Three Metabolic Energy Systems in Training
For Various Running Events