Download Units of Competency

10/12/2013
Energy Systems
The information in this lecture is drawn from this unit of competency:
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SISFFIT305A Apply anatomy and physiology principles in a fitness context
Units of Competency
By the end of this lecture you will be able to...
 Identify energy systems
 Explain how food is converted into energy
 Identify which energy system is used in specific activities
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This lecture will work through the following topics;
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Energy systems
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Anaerobic & Aerobic
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Before discussing the various systems by which your body can provide energy to your muscles, we first need to define what muscle "energy" actually is. 
We know that your muscle cells need an energy source to be able to contract during exercise. 
At the highest level, the energy source for muscle contractions is the food you eat. 2
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A complex chemical process within your cells, called cellular respiration, ultimately converts the energy stored in the foods you eat into a form that is optimized for use at the cellular level of your muscles. 
Once food energy has been converted by cellular respiration it exists at the cellular level in the form of a molecule called adenosine triphosphate (ATP).
Energy from the food we eat is made available for use
through a molecule called ATP - Adenosine Triphosphate
Within the power plants of the cell (mitochondria), energy is
used to add one molecule of inorganic Phosphate (P) to a
molecule of Adenosine Diphosphate (ADP) to produce ATP.
ADP
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ADP + P + Energy ‐‐‐> ATP At the energy‐requiring site, the last phosphate group in the tail is broken off and the energy in the bond liberated. ATP ‐‐> ADP + P + Energy The ADP and the phosphate are then free to return to the power plant and be rejoined. In this way, ATP and ADP are constantly being recycled. 3
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Our cells only have enough ATP stored to last for a few seconds
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Our food can be broken down to provide energy which can be used to make ATP
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There are two energy systems at work in our body at any given time. These systems operate together, however the extent to which one takes over depends on the intensity (primarily) and duration (secondary) of the exercise
ANAEROBICALLY
Without oxygen
AEROBICALLY
With oxygen
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For short bursts of vigorous activity, such as sprinting, the muscles can break down glucose molecules in the absence of oxygen. An anaerobic system is often used for a short period of time when the blood cannot carry oxygen fast enough to the working muscle cells. What happens to glucose? 
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In the absence of oxygen, glucose is only partially broken down by a very complicated series of reactions. In humans, the end product is lactic acid; ATP is also formed. Lactic acid is actually a by‐product, and when it accumulates to high levels, it causes muscular fatigue. The production of ATP, on the other hand, is the sole purpose of glycolysis. 
For every glucose molecule that undergoes glycolysis, a net of 2 ATP molecules is produced. 
This yield represents only about 5 per cent of the total yield possible when the same amount of glucose is completely broken down to CO2 and H2O in the presence of oxygen (aerobic pathway). 
However, this anaerobic pathway, like the Alactic system, is extremely important to us, primarily because it also provides us with a very rapid supply of ATP. 5
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For example, exercises that can be performed at maximum rate for only about 2 or 3 minutes, such as sprints and underwater swimming (breath holding), depend primarily upon the ATP‐PC and lactic acid systems for ATP formation.
Can be separated into 2 further energy pathways
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Alactic – energy produced without the presence of Lactic Acid. This is abbreviated to the ATP, CP, or PCr system
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Lactic – energy produced in the presence of Lactic Acid. Lactic Acid is a by product of the Alactic system and the body resynthesises this as another energy source. Lactate/Lactic Acid is abbreviated to La
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This energy system is the first one recruited for exercise and it is the dominant source of muscle energy for high intensity explosive exercise that lasts for 10 seconds or less. For example, the alactic anaerobic energy system would be the main energy source for a 100 m sprint, or a short set of a weightlifting exercise. 
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It can provide energy immediately, it does not require any oxygen (that's what "anaerobic" means), and it does not produce any lactic acid (that's what "alactic" means).
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It is also referred to as the ATP‐PCr energy system or the phosphagen energy system.
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The alactic anaerobic energy system provides its ATP energy through a combination of ATP already stored in the muscles (about 1 or 2 seconds worth from prior cellular respiration during rest) and its subsequent rephosphorylisation (about 8 or 9 seconds worth) after use by another molecule called phosphocreatine (PC). 
Essentially, PCr is a molecule that carries back‐up phosphate groups ready to be donated to the already used ADP molecules to rephosphorylise them back into reusable ATP. 
Once the PCr stored in your muscles runs out the alactic anaerobic energy system will not provide further ATP energy until your muscles have rested and been able to regenerate their PCr levels
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• Fuel = CP Stores
Stored in muscle
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0‐15 seconds
• Short Duration
• Explosive movements
• 3 minutes recovery
This system is the dominant source of muscle energy for high intensity exercise activities that last up to approximately 90 seconds. For example, it would be the main energy contributor in an 800 m sprint
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Essentially, this system is dominant when your Alactic anaerobic energy system is depleted but you continue to exercise at an intensity that is too demanding for your aerobic energy system to handle. 
Like the alactic anaerobic energy system, this system is also anaerobic and so it does not require any oxygen. 8
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However, unlike the alactic anaerobic energy system, this system is lactic and so it does produce lactic acid. 
It is also referred to as the lactic acid system or the anaerobic glycolytic system.
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In contrast to the alactic anaerobic energy system, which uses ATP stored from previous cellular respiration in combination with a PCr phosphate buffer, the lactic anaerobic energy system must directly recruit the active cellular respiration process to provide ATP energy. 
The cellular respiration process consists of a very complex series of chemical reactions, but the short summary of it is that it ultimately converts food energy (from carbohydrates, fats, and proteins) into ATP energy. 
When oxygen is not available for cellular respiration, as is the case for the lactic anaerobic energy system, lactic acid is produced as a by product.
•Fuel = Carbs
From foods we eat
15 sec –
2 minutes
• Short duration
• 45 seconds –
10 minutes active recovery
Recovery
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Anaerobic glycolysis
Glycogen
Glucose
NB: 2 molecules of ATP are produced
Pyruvic Acid
Insufficient Oxygen
Lactic Acid 
Try rowing on a rowing machine, cycling or sprinting for a short burst (60 – 90 seconds) at 100%.
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Can you feel the lactic acid build up??
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How does it make you feel? 
Can you feel your energy stores kick in? Alactic and Lactic?
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1.
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In your own words – describe “Energy”
What are the 2 ways energy can be made?
Which one uses oxygen?
What is an example of where you would predominately use the anaerobic energy system?
These questions are not assessable. However, having a clear understanding of
key terms and principles for Exercise Science will aid in your learning
journey.
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A system that requires oxygen is called an aerobic system
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During continuous aerobic exercise, your intensity level will be reduced so that the energy demand placed on your muscles equals the energy supply Compared to the Alactic anaerobic and lactic anaerobic systems, where demand usually exceeds supply and energy stores are quickly depleted. 
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A continuous supply of oxygen allows you to maintain a reduced intensity level for a long period of time. If you are able to extend an exercise activity beyond approximately two minutes in length it will be due to the fact that you are working at an exercise intensity level that can be accommodated by your aerobic energy system. By five minutes of exercise duration the aerobic energy system will have become your dominant energy source. As an example, the aerobic energy system would be the main energy contributor to a marathon runner. The aerobic energy system does not produce lactic acid, but unlike the other two energy systems, it does require oxygen.
Just like the lactic anaerobic energy system, the aerobic energy system must directly recruit the active cellular respiration process to provide ATP energy. 12
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Food energy is converted into ATP by your muscle cells through a very complex series of reactions. 
The difference, relative to the lactic anaerobic energy system, however, is that since oxygen is now available to your muscles no lactic acid will be produced as a byproduct. 
The generation of ATP energy by the aerobic energy system can be continued as long as oxygen is available to your muscles and your food energy supplies don't run out.
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In the presence of oxygen, a glucose molecule is completely broken down to CO2 and H2O and a total of 38 molecules of ATP is produced. 
Two of these molecules of ATP come from glycolysis. 
This may come as a surprise to you since we just said that glycolysis is an anaerobic pathway.
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Actually, there is only one difference between the anaerobic glycolysis we discussed earlier and the glycolysis that occurs when there is a sufficient supply of oxygen ‐‐ lactic acid does not accumulate in the presence of oxygen. 
In other words, the presence of oxygen inhibits the accumulation of lactic acid but not the formation of ATP.
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Oxygen does this by diverting the majority of the lactic acid precursor, pyruvic acid, into the aerobic pathway after the ATP is formed. 
It is in the aerobic pathway that glucose, which has already been broken down to pyruvic acid, is further broken down to CO 2 and H 2 O, with the simultaneous production of additional ATP
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• Fuel = Carbs, Fats, Proteins
2 minutes onwards
• Long Duration
From foods we eat
• As long as it takes to replace fuel
Recovery
Aerobic glycolysis
Glycogen
Glucose
KREBS CYCLE
36 ATP + Carbon dioxide + water
Pyruvic Acid
Oxygen
NB: 38 molecules of ATP are produced from the breakdown of 1 glucose molecule 14
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ENERGY
SYSTEM
DURATION
FUEL
LIMITATIONS
/WASTE
RECOVERY TIME
Alactic System
1‐15 seconds
Creatine Phosphate
Depletion of CP stores
3‐5 minutes
Lactic System
15 seconds‐ 2 minutes
Carbs
Lactic acid accumulation
45 seconds –
10 minutes
active recovery
Aerobic System
2 minutes onwards
Carbs, fats, proteins
Lactic acid As long as it accumulation, takes to replace fatigue
fuel
Often referred to as MVO2
Is the maximal amount of Oxygen your body can use to produce the greatest continuous output or effort.
 Usually reported as mL/min/kg (relative) or L/min (absolute)
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o 35 mL/min/kg is considered average
o 65 mL/min/kg is considered elite level
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Ability to uptake and transport O2
Max volume of O2 consumed per minute during exercise
Ability of muscles to use O2
Anaerobic Threshold
• The highest intensity of exercise where lactate production equals lactate resynthesis
Steady State
• When O2 consumption plateaus at a level to maintain aerobic metabolism
EPOC
• Excess Post‐exercise Oxygen Consumption
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The point where the body cannot supply oxygen as fast as it is needed to produce aerobic energy, so the body is forced to produce energy from the anaerobic system. 
This causes lactic acid accumulation.
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The fitter the individual, the longer it will take to reach anaerobic threshold.
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Is a by product of anaerobic glycolysis
Causes muscle fatigue
Lactic acid is removed from the blood and muscles during recovery, with the removal being faster when active recovery is performed Lactic acid enters the blood stream and goes to the liver where it is converted back into glycogen 
The mitochondria in the muscle cells are responsible for breaking down glucose for usable energy. 
This demand for usable energy increases as the workload increases. 
This demand for energy is met by increases in oxygen consumption as the result of increased respiratory rate (RR) and heart rate (HR) 
Both of these variables (RR & HR) increase linearly with oxygen consumption up to the point of maximal oxygen consumption (VO2max) during a graded exercise bout. 17
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When exercise workload is constant, however, there is a predictable curve that includes a plateau of HR and BR during the phase of exercise known as stead state. This plateau is the result of the energy demand of the workload being met at a certain HR and BR. When an exercising subject goes from rest to exercise their physiological systems cannot reach steady state immediately because there is a lag time when the HR and BR need to catch up.
The HR and BR will increase sharply until steady state is met. Rest
Recovery
Steady State
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Essentially, the workload and energy demands are greater than can be met through aerobic means, and must be supplemented through the anaerobic breakdown of stored glycogen and creatine phosphate. 
The volume of O2 deficit is dependent upon many factors including workload/exercise intensity, ambient conditions such as temperature and humidity, and subject fitness level.
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Oxygen debt The difference between oxygen demand and oxygen consumed is called oxygen deficit. Once exercise ceases extra oxygen is still consumed to repay the oxygen deficit that occurs before steady state is reached. This is known as Excess Post‐exercise Oxygen Consumption (EPOC).
The extra oxygen is used for a number of tasks:
 To replenish oxygen reserves
 To convert lactic acid into pyruvic acid
 To replace glycogen stores
 To replenish creatine phosphate stores
 Re‐oxygenation of venous blood.
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EPOC has two components – a fast component and a slow component
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Fast component: This is the initial component and utilises up to 4 liters of oxygen. The main functions of this component are:
Replenish myoglobin and haemoglobin stores.
Restore ATP and CP stores to resting levels.
 Provide energy for increased ventilation and elevated heart rate.
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2. Slow component: This component may take hours or up to one day. It utilises between 5‐14 litres of oxygen. The main functions are:
Convert lactic acid to pyruvic acid and glycogen.  Replenish glycogen stores.  Repair tissue damage.
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Fast Component
Slow Component
Myoglobin and Oxyhaemoglobin
Convert lactate to pyruvate and glycogen.
ATP and CP stores
Replenish glycogen stores
Increased ventilation and HR
Repair damaged tissues
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Please ensure you have taken notes (if applicable) and understand the principles outlines in this lecture.
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Look at your Work Book for learning tasks and activities that relate to this specific Lecture.
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Complete your online exam
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Complete all the logbook tasks for this topic
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Time to move on to the next topic!
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