LEWIS: Aerobic Energy System Flashcards
In order to move our muscles need to
contract
For our muscles to contract they need a supply of
energy
The energy we need for muscle contractions is supplied to us in the form of food which is broken down within cells to release energy that is used to form
chemicals
These chemicals can be broken down to release the energy stored within them, therefore the body uses
chemical energy
Muscles use the chemical energy stored in specific compounds to move. The body then converts the energy found into a form that it can
handle
The immediately/directly usable form of chemical energy for muscular activity is
Adenosine Triphosphate (ATP)
It’s the body’s job to transfer the chemical energy stored in the food we eat into the suable energy found in ATP. Energy is released when ATP is
broken down
Energy is required when ATP is
resynthesised
The breakdown of ATP releases
adenosine diphosphate (ADP) and phosphate (P)
Equation for ATP breakdown:
ATP -> ADP + P + ENERGY
The body then rebuilds/re-synthesises ATP from the breakdown products:
ADP + P + ENERGY -> ATP
When a muscle fibre needs ATP to supply the energy for the fibre to contract, that ATP has to be
produced or resynthesised right away
Able to resynthesise ATP from 3 different types of chemical reactions that take place within the muscle cells:
2 depend on the food we eat
3rd relies on phosphocreatine found in muscles
Everyday tasks uses energy that involves chemical reactions that use
oxygen
Using oxygen in order to produce the ATP that we need is said to involve
aerobic processes
We obtain our energy from the food we
eat
6 classes of food - 3 which can be used as energy sources:
Fats
Carbohydrates
Proteins
Carbohydrates broken down/digested to
glucose
Glucose is the main form of carbohydrate found in the body and dissolves in
blood plasma
Fats broken down/digested to
Fatty acids and glycerol
Fats are stored in cells that make up a special tissue mainly found under the skin and surrounding major organs known as
adipose tissue
When fats are stored and used as an energy source they are known as
triglycerides
Proteins are digested into
amino acids
These energy sources once broken down then enter the blood system and become available for the
body
Carbohydrate -> glucose dissolves into the blood plasma and circulates around the body in the blood system
This glucose may be used by
all cells and tissues, including working muscles, as an energy source for the resynthesis of ATP
Any excess glucose that enters the blood following digestion of a meal may be stored in
muscles and liver as glycogen
glycogen may also be used as a source of ATP by muscles as it is
easily and quickly broken down into glucose
When our liver and muscle glycogen stores are full, any excess glucose from digestion is converted into fat droplets and stored in
adipose tissue
The glycerol and fatty acids (called free fatty acids when in the blood) that are formed during fat digestion may be used directly from the blood, but most are converted back into
fats and stored as triglycerides in adipose tissue
Glycerol may be converted into glucose which is what happens when the diet is lacking in carbohydrate or when
glycogen stores have been depleted as may happen during long-duration exercise that demands continuous energy supplies (e.g. a marathon)
Amino acids (breakdown products of proteins) are usually used by the body for
growth and repair
Unlike carbohydrates and fats, amino acids cannot be stored, instead they are
broken down by the liver, and the nitrogen-containing part of the molecule is excreted as urea
When we exercise, the part of the amino acid left after the urea has been removed may be
converted into glucose or used in some stage of the energy production system
Interconversions of the energy sources are mainly a function of the
liver
Some conversions are easier than others, thus the liver readily converts excess glucose into fat, but less readily into
glycogen
Reverse reactions, the conversion of glycogen into glucose is easily done in the liver, but less readily accomplished in
muscles
Resting 1/2 - 2/3 of our energy comes from
fats
Resting 1/2 - 1/3 of our energy comes from
carbohydrates
Ratio of energy sources changes when exercising, but the exact proportions depends on many factors such as:
- Type of exercise
- Type of diet
- Performer’s fitness level
- Type of muscle fibres involved in the exercise
Provided that the supply of oxygen to the muscles can be maintained, the complete breakdown of glycogen and glucose to provide energy for ATP resynthesis is
possible
Breakdown of glycogen and glucose using oxygen is said to be an
aerobic process
Exercising muscles can obtain carbs from
glycogen stored in the liver and muscles
glucose circulating in the blood
fat either circulating in blood or stored in adipose tissue
Most of the glycogen stored in the liver is used for
an emergency supply for the brain in case blood glucose levels fall
The use of protein as an energy source is fairly complex but also happens to be small enough to be
negligible
Problems with using glycogen as an energy source are:
- stores are limited
- muscle fatigue occurs rapidly when stores are depleted
Muscle glycogen stores are fully depleted with any exercise that lasts longer than
2 hours
During recovery from exercise, there is an initial rapid replacement of used glycogen, but complete recovery may take more than
24 hours
The longer an exercise lasts (more endurance based it is) the more we tend to use
fats as an energy source
Fats may only be used as an energy source if
oxygen is present
The use of fat as an energy source therefore depends on the supply of oxygen to the
muscles
In slow-twitch muscle fibres, especially, fat is the main source of energy during most activities that last
longer than 1 hour
Because training increases the body’s capacity to supply oxygen to the working muscles, it also increases the muscle fibres’ ability to use
fats as an energy source
Glycerol and fatty acids need to be supplied by the blood when used as
energy sources
Glycerol released from fat stores may enter the energy pathways or be converted into
glucose for use in the normal way
Adipose tissue releases free fatty acids, which are transported around the blood, bound to
proteins
Molecules of glucose, glycogen and fats are completely broken down in the presence of
oxygen
Complete breakdown of carbs and fats produces:
- carbon and oxygen (CO2)
- Hydrogen and oxygen (Water)
- energy for ATP resynthesis
Majority of ATP production is confined to
mitochondria
Muscle cells tend to have large numbers of
mitochondria
The aerobic production of ATP has 4 advantages over other systems:
- No fatigue by-products
- Abundant supply of starting chemicals
- 36-38 ATP molecules gained from 1 ATP
- Slow twitch fibres provide a continuous supply of energy over a long period of time
1st stage of aerobic system:
Glycolysis
Glycolysis involves:
- Glycogen broken down into glucose
- Production of pyruvic acid (pyruvate)
Glycolysis takes place in the
sarcoplasm of muscle cells
During glycolysis how many ATP molecules are made for each molecule of glucose?
4
Pyruvic acid formed during glycolysis is added to the enzyme
coenzyme A (CoA)
Pyruvic acid + CoA =
acetyl CoA to allow it to enter the next stage
2nd stage of aerobic system =
Krebs cycle
Krebs cycle occurs within the
mitochondria
The Krebs cycle consists of a series of 8 enzyme-driven reactions that oxidise acetyl CoA to
carbon dioxide
(KC) Hydrogen atoms that are part of acetyl CoA are transferred to chemicals called
hydrogen carriers
(KC) Hydrogen carriers eventually enter the next stage of aerobic metabolism known as
the electron transfer chain
In the ETC a series of carrier molecules are involved in the oxidising of the hydrogen contained within the hydrogen carriers, producing water as a by-product and generating a large supply of ATP:
34 molecules of ATP for each glucose molecule
Pyruvic acid from glycolysis eventually becomes converted into CO2 and water and large amounts of energy are released in the form of ATP - this process requires large amounts of
oxygen for its completion
Fatty acids from the breakdown of triglycerides are themselves broken down within the sarcoplasm by a process called
beta-oxidation
Beta-oxidation is the breakdown of fats into
acetyl CoA within the sarcoplasm
(BETA-OXIDATION) acetyl CoA can then enter the KC and eventually the ETC for
ATP production
During exercise, reliance on fats diminishes dramatically in explosive sports, but in endurance events the mixed use of
fats and carbs = important
Mix of carbs and fats depends on 4 factors:
intensity
duration
athlete’s level of fitness
diet and nutritional status
1st stage of fat break down is the beta-oxidation of these free fatty acids into acetyl CoA. This ‘prepares’ the fatty acid for entry into the
mitochondria
Final result of fat break down once fatty acid is in mitochondria =
water and carbon dioxide are produced
Energy is released from ATP resynthesis
If exercise is slow continuous activity, fats can be the
main energy source
Fat requires more oxygen for breakdown than glucose as it has more carbon atoms in its structure. Aerobic processes convert those carbon atoms into
co2
Limited oxygen supply =
limits KC and ETC
Limited oxygen supply occurs during
intensive exercise
When there is not enough o2 available, the preferred energy source =
glucose
Appropriate training increases the body’s ability to
take in oxygen to the muscles and therefore increase the ability to use fat for energy
Limitations of fat as an energy source:
- Unavailable in limited oxygen supplies (explosive exercise)
- Fat stores = excess non-functional weight
Endurance training increases the body’s ability to
release free fatty acids from their fat stores - trained performer can use more fats for energy than untrained
Breakdown of fats requires carbs presence as they enable the KC within the mitochondria to
operate
Demand for energy remains high during prolonged, continuous exercise, glycogen stores become depleted and the breakdown of fats will slow because of the
lack of carbs
When glycogen stores have depleted and KC slows as a result as well as ATP resynthesis, it is known as
‘hitting the wall’
Disadvantage of fats:
-Can restrict joint movement
11 Adaptations due to training:
- cardiac hypertrophy
- increased resting stroke volume
- decreased resting HR
- reduced exercising and maximal heart rate
- increased blood volume and haemoglobin
- increased muscle stores of glycogen and triglycerides
- increased myoglobin content in muscles
- increased capillarisation of muscle
- increased number and size of mitochondria
- increased concentrations of oxidative enzymes
- beta-oxidation becomes more efficient
As a result of adaptations following training what increases:
VO2 max
VO2 max is the
maximum amount of oxygen consumed and utilised per minute
VO2 max is also known as
aerobic capacity
fuels used in
GLYCOLYSIS =
KREBS CYCLE =
GLYCOGEN/GLUCOSE
FATTY ACIDS
Molecules of ATP produced in:
GLYCOLYSIS =
KREBS CYCLE =
ELECTRON TRANSPORT CHAIN =
2
2
34
2 Drawbacks of aerobic energy system:
- presence of oxygen = lower intensity or 3 minute threshold
- relies heavily on glycogen stores initially
training methods for aerobic energy system:
- continuous training (60-80% max HR)
- low intensity fartlek training
What sports use aerobic energy system:
1500m
marathon
When we exercise, or even when we are at rest, our bodies are using oxygen to
Resynthesise ATP
ATP is needed for:
The heart
The muscles of respiration to contract
Keep brain functioning
The amount of oxygen used by the body to produce ATP is called
Oxygen consumption
When we begin to exercise we need more ATP and therefore use more oxygen so our
Oxygen consumption increases
When we exercise, or even when we are at rest, our bodies are using oxygen to
Resynthesise ATP
ATP is needed for:
The heart
The muscles of respiration to contract
Keep brain functioning
The amount of oxygen used by the body to produce ATP is called
Oxygen consumption
When we begin to exercise we need more ATP and therefore use more oxygen so our
Oxygen consumption increases
