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Aerobic fitness refers to a persons capacity to take up and use sufficient oxygen to sustain work for long periods. Work in this case
meaning physical activities, including exercise.
The function of respiration is to get oxygen from the air into body cells where it can be used in a chemical reaction that releases energy
, and to remove carbon dioxide a waste product of this reaction. Respiration is broken down into three section:
- External respiration
- Oxygen transport
-Oxygen use/ uptake
External respiration involves inspiration (breathing in) and expiration (breathing out). The process of breathing in and out is called
ventilation. The air that a person inspires contains a mixture of gases, including oxygen. It is only the oxygen that a person needs. Some
of the oxygen in inspired air is absorbed by the lungs. The air expired contains carbon dioxide and less oxygen than inspired air.
The inside surface of the lungs comprises a large number of tiny sacs, called alveoli. The wall, or membrane of each sack is damp and has
a good blood supply just below the surface. Some of the inspired air defuses across this membrane and into the blood, where it
combines with the iron-containing protein haemoglobin. At the same time, carbon dioxide in the blood diffuses the other way across the
alveolar membrane and is expired.
The oxygen that has become combined with the haemoglobin (oxyhaemoglobin) needs to be transported to all parts of the body. Blood
from the lungs enters the heart, from where it is pumped via arteries around the body and into the blood cells.
In the body's cells, oxygen combined with other chemicals from food release energy. In the case of muscle cells, this is mechanical
energy for movement. Glucose (which is also carried by the blood to body cells) combines with oxygen to produce energy as well as
waste products carbon dioxide and water. The carbon dioxide then diffuses into the blood and its transported via veins back to the heart
and then to the lungs. Some of the glucose used to fuel energy release in muscle cells is carried to these cells by the circulatory system.
Muscles also contain stores of another fuel called glycogen. Glycogen consists of long chains of glucose molecules, which can easily be
broken down to create glucose again. Fatty acids can be used to fuel muscle actions, in a sequence of reactions that create energy,
carbon dioxide and water. Fatty acids are an important fuel for energy release explains why exercise helps to control weight by reducing
the amount of fat stored in a persons body.…read more
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Aerobic and Anaerobic cellular respiration
The chemical process in which energy is produced from glucose are complex. In, outline cellular respiration begins with a process
called glycolsis, in which glucose is converted into a compound called pyruvate. This happens without oxygen and is the key
process in anaerobic (without oxygen) respiration. If sufficient oxygen is present, the pyruvate is oxidised in a series of
biochemical reactions known as the Krebs cycle. This happens during aerobic respiration. It is more efficient than anaerobic
respiration , i.e. It produces more energy from the same amount of glucose.
Given sufficient oxygen ,more energy is produced by aerobic respiration. However, when their is an insufficient supply of oxygen,
the balance of cellular respiration shifts towards anaerobic respiration. This happens when a person exercises at a rate that
exceeds the rate of anaerobic threshold, i.e. The body's aerobic capacity to support cells with oxygen continuously, for
example, running at maximum speed for around 10 minutes requires anaerobic respiration. Anaerobic respiration requires
lactic acid, which builds up in the tissue muscles. This is later broken down (oxidised) when additional oxygen becomes
available, usually when exercise stops or slows down.
Aerobic fitness and external respiration
The level of a persons aerobic fitness is influenced by the capacity of the body to carry out all the respiratory processes described
above. The effectiveness of ventilation depends on the person's ability to expand the lungs, as well as the overall lung capacity. The
ability to expand the lungs depends partly on the strength of the relevant muscles, i.e. The diaphragm and ribcage, as well as the
flexibility of the ribcage.
Aerobic fitness and oxygen transport
The effectiveness of oxygen transport in the body, depends on the condition of the heart, arteries, veins and capillaries. This is sometimes
called `cardiovascular fitness'. It includes factors such as maximum rate at which the heart is able to pump and the stroke volume, i.e. The
volume of blood the heart can pump in one beat. , a large, strong heart has a larger stroke volume, than a small, weak heart.…read more
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Short-term effects (during exercise) Long-term effects (over weeks/months)
Decreased blood pH Increased endurance
Increased rate of ventilation Increased capacity to do work
Breathing through mouth Increased lung capacity
Deeper breathing Increased rate of oxygen transfer
Increased heart rate Increased maximum heart rate
Increased stroke volume Increased stroke volume
Dilation of capillaries in skeletal muscle Reduced resting pulse rate
Sweating Reduced stress on the heart
Flushing Increased elasticity of blood vessels
Increased number of capillaries in muscles
Increased size of skeletal muscles
Decrease in adipose tissue (body fat)…read more
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Measuring Aerobic fitness
· Aerobic fitness is measured by VO2 max. This is a measure of the maximum volume of oxygen (o2) a person can use per
minute per kilogram of blood mass during exercise.
· VO2 max is found by measuring the amount of oxygen a person uses per minute during the most strenuous exercise they
· The usual technique for this is for a person to breathe air through a mask into a flexible tube connected to a gas analyser
whilst running on a treadmill or a running machine that is gradually speeding up.
· The persons oxygen use will be at maximum at the point where the person can only just keep up . The gas analyser
measures the rate of flow of oxygen and carbon dioxide in the expired air and produces a continuous reading of the rate of
· The person must also be weighed.
· From this, the VO2 max is calculated dividing the volume of oxygen used (in millilitres per minute) by the persons body
weight in kilograms). The reason for taking body weight into account is to allow comparisons between people of different
sizes and builds.
· As most of the oxygen used during exercise is used by the muscles, people with higher proportions of muscles compared
with fat have the higher VO2 max.
Volume of energy used in millilitres per minute
Body weight in KG…read more
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Other factors affecting aerobic fitness
As adults grow older, lung capacity and cardiac output decline. For example, a simple estimate of
a person's maximum heart rate is to subtract the person's age in years from 220 bpm.
On average, males have the higher VO2 max scores compared to females. This is because females
have a higher proportion of body fat compared with muscles than males. In particular,
women tend to have a thicker layer of subcutaneous fat than men.
There are significant differences between individuals in how effectively body systems work,
including the ability to build muscles. These differences are partly influenced by a persons
Some diseases, especially in the lungs, reduces aerobic fitness. Other conditions, such as obesity,
have an indirect effect restricting exercise.…read more