Laura Spenceley
Task 1 – Energy Systems
Tom Cross
Aerobic Energy System
The aerobic energy system uses fats, carbohydrates and sometimes proteins to resynthesize
ATP. The aerobic energy system produces far more ATP than other energy systems however
it produces ATP at a much slower rate so cannot produce ATP at the rate needed to fuel
intense exercise.
The aerobic energy system is comprised of 3 main stages;
1. AEROBIC GLYCOLYSIS
 Purpose – to break down glucose to form 2 pyruvates.
 Where – glycolysis takes place in the cytoplasm and requires no oxygen.
Stages of aerobic glycolysis:
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Glycolysis – the process of the breakdown of 6-carbon glucose into two 3-carbon pyruvic
acid units.
The hydrogen ions removed join with the hydrogen carrier NAD to form NADH2.
Whilst some energy is needed to begin glycolysis there is an overall net gain of 2 ATP.
The pyruvic acid (3C) enters the matrix of the mitochondrion where it is oxidized (i.e. 2H
removed) and a carbon dioxide is lost. This process forms a two carbon molecule called
acetyl-CoA (2C).
The hydrogen ions which have been removed join with NAD to form NADH2.
2. THE KREBS CYCLE
 Purpose - to produce energy carrier molecules such as NADH.
 Where – takes place in the mitochondria and requires oxygen.
Laura Spenceley
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Task 1 – Energy Systems
Tom Cross
Stages of The Krebs Cycle:
Acetyl-coenzyme A enters the Krebs cycle.
Acetyl-Coenzyme A is broken down into carbon
dioxide (a waste product which is expelled through
breathing) and hydrogen.
2 more ATP are synthesised during this process and
made available to fuel further muscle contractions.
Hydrogen is transferred to the electron transport
chain.
3. ELECTRON TRANSPORT CHAIN (ETC)
 Purpose – Produces 34 molecules of ATP for every 1 glucose molecule
 Where 
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Hydrogen ions from Krebs cycle are carried to the electron transport chain by carrier
molecules.
Hydrogen ions are transferred to carrier molecules embedded in the electron
transport chain where they go through a series of chemical reactions.
A hydrogen ion gradient is created. As hydrogen ions move across this gradient
another form of ATPase phosphorylates ADP (adds another phosphate group) to
form ATP.
Water is created as a by-product as hydrogen combines with oxygen.
Aerobic metabolism fuels the majority of the energy needed for long endurance activity. It
utilises oxygen to convert nutrients to ATP. This system is slower than the anaerobic
systems because it relies on the circulatory system to transport oxygen to the operating
Laura Spenceley
Task 1 – Energy Systems
Tom Cross
muscles before it creates ATP. The aerobic metabolism is used primarily during high
endurance exercise, which is usually less intense and can continue for long periods of time.
During exercise an athlete will move through these metabolic pathways. As exercise begins,
ATP is produced via anaerobic metabolism. With an increase in breathing and heart rate,
there is more oxygen available and the aerobic metabolism begins and continues until the
lactate threshold is reached. If this level is surpassed, the body cannot deliver oxygen
quickly enough to generate ATP and anaerobic metabolism kicks in again. Since this system
is short-lived and lactic acid levels rise, the intensity cannot be sustained and the athlete will
need to decrease intensity to remove lactic acid build-up. This can be shown when
comparing long distance running and short sprints. Whilst exercising aerobically, such as
long distance running, an athlete’s energy requirements remain at a steady state
throughout therefore they can run continuously at this steady rate, as soon as they begin to
run at a quicker pace their energy requirements change and they begin to work
anaerobically.
Spencer and Gastin tested highly
trained males who were
specialists in one of the distances
(200m, 400m, 800m and 1500m)
which were to be tested for their
investigation. Their aim was to
find the overall contribution from
the aerobic and anaerobic energy
systems for different length of
distance run. It was expected
that the shorter, more intense
runs would have a higher
anaerobic contribution than the longer, less intense runs which had a higher aerobic
contribution. As expected the results from their investigation showed that the shortest
duration/distance event relatively required the least amount of aerobic contribution whilst
the longest duration/distance event relatively required the highest amount of aerobic
contribution.
Laura Spenceley
Task 1 – Energy Systems
Tom Cross
LACTIC ENERGY SYSTEM
As shown above in the Aerobic Energy System when we exercise, the body converts
glycogen in to ATP which is used to provide energy for the muscles to contract with the
support of oxygen. Once those stores are depleted, the body resorts to an alternate source
of energy; anaerobic energy systems.
The lactic energy system is sometimes known as Anaerobic Glycolysis due to the initial
process being the same as aerobic glycolysis only without oxygen. As before 10 chemical
reactions occur within the sarcoplasm which turns Carbohydrate into Pyruvic acid and 2
molecules of ATP. The difference now being the lack of oxygen meaning the carrier molecule
NAD+ cannot offload the Hydrogen (H+) by-product of glycolysis causing a build-up in the
cell. To try to prevent an increase in acidity the pyruvic acid accepts the H+, forming Lactic
acid. If oxygen was present the H+ would be transported to the Mitochondria for use in the
Kreb's cycle. Lactic acid is thought to interfere with muscle contraction due to disrupting the
binding of Calcium to Troponin. Acidity also stimulates free nerve endings within the
muscle, causing pain. Due to lactic acid production, this energy system can only be
predominant for up to 2 minutes.
Following anaerobic exercise, despite the
metabolic process used not requiring
oxygen, your body will be in an Oxygen debt
meaning respiration rate will be very high.
The liver is responsible for clearing up the
lactic acid build up that develops. Your body
produces lactic acid as a safety precaution
when you remain in a constant anaerobic state
to prevent muscle contractile failure. The
diagram left shows the process in which the liver
prevents lactic acid build up to avoid any long
term issues with a build-up of lactic acid.
http://thefitnessgrail.wordpress.com/2012/04/01/lactic-acid-training-for-fat-loss/
Laura Spenceley
Task 1 – Energy Systems
Tom Cross
ANAEROBIC ENERGY SYSTEM
The Anaerobic energy system is also known as the Phosphocreatine energy system. The
system utilises Creatine phosphate to create ATP. ATP is a high-energy compound which is
stored in regulated quantities within the muscle. The high energy phosphate bond in
Creatine Phosphate is broken down to release energy and is immediately used to recreate
ATP. The anaerobic energy system acts as a reinforcement system for ATP as it helps
regenerate ATP from ADP immediately. The Creatine Phosphate stores within the muscles
are extremely limited whilst providing enough energy for 5 – 12 seconds of work at
maximum intensity. Once this process has been completed the Creatine Phosphate will
then need to be regenerated. Other useful fuels such as fat and glycogen are required to
supply energy for the effective regeneration of ATP.
The anaerobic energy system is used in sports which require explosive movements as it is
able to provide an instant rush of activity lasting a few seconds. Sports which will use this
energy system effectively may be;
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100m Sprints
Javelin
Long Jump
High Jump
Weight lifting