aerobic and anaerobic energy systems
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Aerobic and Anaerobic Energy Systems. Learning Objectives: To be able to explain how energy is produced when oxygen is present. To be able to name and describe the two anaerobic energy systems. Adenosine Triphosphate (ATP). The body transforms the food we eat into ATP. - PowerPoint PPT PresentationTRANSCRIPT
Aerobic and Anaerobic Energy Systems
Learning Objectives:• To be able to explain how energy is produced when
oxygen is present.• To be able to name and describe the two anaerobic
energy systems.
Adenosine Triphosphate (ATP) The body transforms the food we eat into ATP. When ATP is broken down it releases ADP + P +
energy. The body can resynthesise ATP by the reverse
reaction: ADP + P + energy = ATP. The body cannot store much ATP (only enough
for about 2-3s of intense activity) so any energy required needs to be produced immediately.
Our Fuel
• We create energy from the food we eat.• ATP can be produced using carbohydrates, fats
or protein.• These cannot be used until they have been
broken down into glucose, fatty acids and amino acids, respectively.
• Excess glucose is stored in muscles and liver as glycogen.
Aerobic Energy Production from Glucose
• When oxygen is present the complete breakdown of glucose is possible.
• This occurs in the mitochondria and produces CO2, H2O, and energy.
• The advantages of aerobic energy production is that there are no fatiguing by-products, the energy sources are usually abundant and lots of ATP can be produced.
• The breakdown of glucose into energy (ATP) involves 3 stages: glycolysis, Kreb’s cycle, and the electron transport chain.
Glycolysis• The initial stage of glucose
breakdown (occurs in sarcoplasm).• This stage is identical in both the
aerobic and anaerobic systems).• Some complicated reactions take
place but all you need to know is….• Pyruvic acid is produced (pyruvate).• 2 ATP are used and 4 ATP produced.
Kreb’s Cycle• This follow’s on from glycolysis and
only occurs in the presence of oxygen.• Pyruvic acid from glycolysis is added
to coenzyme A to produce acetyl coenzyme A to start the cycle.
• 8 enzyme driven reactions occur to change acetyl coenzyme A into CO2.
• H atoms (which were part of acetyl coenzyme A) go on to the electron transport chain.
Electron Transport Chain• The final stage of glucose breakdown.• The H atoms from Kreb’s cycle are oxidised
(join with oxygen) to produce water (a by-product) and large amounts of ATP (32 molecules)
• Large amounts of oxygen are required at this stage (thus it is aerobic energy production).
Summary of Aerobic Energy Production from Glucose
• At the end of the 3 stages 38 molecules of ATP are produced and 2 are used (net production = 36 ATP).
• Glucose is broken down into pyruvic acid (glycolysis), then acetyl coenzyme A, and this is broken to form carbon dioxide (CO2), water (H2O) and energy to resynthesise ATP.
• Remember that glycolysis occurs in the sarcoplasm whilst Kreb’s cycle and ETC occur in the mitochondria. Muscle cells therefore have a large number of mitochondria.
Aerobic Energy production from Fat • Fatty acids are broken down by a process called beta-
oxidation to acetyl CoA which enters the Kreb’s cycle (and eventually electron transport chain).
• Even more ATP can produced from fat than from glucose (during electron transport chain) but far more O2 is required.
• The fatty acids we use are in the blood (very little is stored in muscles).
• Anymore fatty acids needed are taken from our adipose tissue (fat stores).
• Endurance training makes us better at releasing fat from adipose tissue. This is why long duration, low intensity exercise ‘burns’ fat.
So why not always just use Fat?Fatty acids release huge amounts of energy but:• Fatty acids cannot be broken down without oxygen
(aerobic only) so it is useless for high intensity exercise.• Extra fat means extra weight and this requires energy
to carry around.• Excess fat can cause overheating.• Kreb’s cycle will not operate without glucose being
present so fat cannot be used without at least some glucose.
• This is known as ‘hitting the wall’, when glucose stores totally run out and all energy production stops.
Anaerobic Energy Systems• When the body is unable to provide the oxygen
required to resynthesise ATP it must start to work anaerobically.
• There are two anaerobic energy systems:
1. Phosphocreatine (PC) energy system (or ATP-PC system)
2. Lactate anaerobic energy system
Phosphocreatine (PC) Energy System (or ATP-PC system)
PC → P + C + Energy AND Energy + P + ADP = ATPFor every molecule of PC broken down, one molecule of ATP
can be resynthesised.No oxygen is required.Energy is released very rapidly (as almost no reactions take
place) and there are no waste products.Stores only last for 5-8s of high intensity exercise.It is therefore excellent for very high short intensity
activities (e.g. 100m sprint) but not for anything longer.PC can be resynthesised quickly. 50% in 30s, 100% in less
than 4 mins (this requires O2 so intensity must be reduced).Creatine supplements allow us to work harder for longer (by
increasing PC stores), thereby improving strength.
Lactate Anaerobic Energy System
• This system involves the partial breakdown of glucose (oxygen is required for full breakdown).
• 2 molecules of ATP are produced (18 times less than aerobic!) as glucose only goes through the glycolysis stage.
• Lactic acid is produced as a by-product (causes pain).• This system can therefore only be sustained for
between 10 seconds and 3 mins.• Few chemical reactions involved so energy can be
produced quickly.
How/Why is Lactic Acid Produced?Hydrogen is released during both glycolysis and the Kreb’s cycle
(remember that both the aerobic and anaerobic systems can operate at the same time).
These H atoms combine with oxygen (in the electron transport chain).
At some point there becomes too many H atoms for the amount of O2 available. Excess H atoms combine with pyruvate (from glycolysis) to form lactic acid.
This point is the lactate threshold (2 mmol per litre of lactic acid above resting levels).
The build up in lactate acid is a contributing factor for fatigue. It produces an acidic environment which slows down enzyme activity and stops the breakdown of glucose. It also effects nerve endings causing some pain.
The fitter we are and the higher our VO2 max, the longer we can resist lactic acid forming and so the higher our lactate threshold.
Summary of the 3 Energy SystemsATP-PC System Lactic Acid System Aerobic System
Anaerobic Anaerobic Aerobic
Very quick ATP production Quick Slow
ATP and PC Glucose Glucose and fat
No by-products Lactic acid No fatiguing by-products
Short duration (0-10s) 10s – 3mins Up to 2 hours
High intensity (95-100% max) High intensity (60-95%) Low intensity (up to 60%)
Quick recovery (30s – 3min) 20 min – 2 hours Up to 24 hours to replenish glycogen stores