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HOME CONTENT PREPARATION ANALYSIS DESIGN APPENDICES GLOSSARY
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SECTION II - ANALYSIS
LESSON 6 - FLEXIBILITY LESSON 7 - ENDURANCE LESSON 8 - STRENGTH LESSON 9 - SKILL
LESSON 10 - BODY COMPOSITION LESSON 11 - ENERGY LESSON 12 - NUTRITION LESSON 13 - STRATEGY
ANALYSIS OF CARDIORESPIRATORY ENDURANCE
Objectives
Upon completion of
Lesson 7, you will be able to demonstrate the following objectives:
v Describe the flow of blood through pulmonary and systemic circulation.
v Explain
how cardio respiratory endurance is assessed.
v Explain
the relationship between VO2 max and level of physical activity.
v Explain the FIT model of fitness training as it relates to cardio respiratory endurance.
v Explain the meaning of perceived rate of exertion. and compare it with the target heart rate zone, as a method of managing the intensity of training.
The cardio respiratory system
contributes to the energy producing processes of the body by delivering oxygen
and other nutrients to exercising muscle cells and removing carbon dioxide and
other waste products from the muscles. However, it is the electrochemical
energy produced, when the heart, lungs, blood vessels, and blood perform their
roles, that makes the vital functions of the cardio respiratory system
possible. Therefore, knowledge of the processes at all levels of the
organizational structural hierarchy of the body is the basis for understanding
of how the cardio respiratory system responds to physical activity.
In this lesson you will learn about the functions of the cardio respiratory system and how this system affects the production of energy and is changed in response to physical exercise. The primary roles of the cardio respiratory system are cardiac output, ejection fraction, and oxygen extraction. Each of these functions represents the efficiency of the cardio respiratory system, which involves how the heart, lungs, blood vessels, and blood work to achieve higher levels of performance and to sustain life.
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Heart, Lungs, Blood Vessels, and Blood
The cardio respiratory system
is primarily a transport network in the body. The blood that it transports
serves as the vehicle to carry gases (such as oxygen) and nutrients (such as
fats, amino acids, and glucose, nutrientsthat produce energy)
from where they are taken into the body to the cells where they are needed.
Blood also picks up lactic acid and carbon dioxide from the cells where
they are made and carries them to where they can be expelled or metabolized
(chemically changed). Therefore, one of the many goals of a high level of
cardio respiratory endurance is improved transport of nutrients and waste via
the heart, lungs, blood vessels, and blood.
The heart is a muscle that is
divided into right and left sides, and each side is further divided into upper
and lower chambers, making a total of four separate chambers. These four
chambers are responsible for transporting blood throughout the body. To
accomplish circulation, the two sides of the heart establish two circulatory
patterns: pulmonary circulation, movement of blood to the lungs and back
to the heart and systemic circulation, the flow of blood from the left
ventricleto the rest of the body and back.
During systemic circulation
the right and left ventricles pump at the same time shortly after the atria
pump blood into the ventricles. When blood is moved from the ventricles,
each side pumps the same amount of blood per contraction. Diastole,
which refers to the relaxation phase, occurs after the heart contracts. During
diastole, the heart muscle itself is supplied with its blood flow (its supply of
oxygen) through the coronary arteries. How well the heart supplies
oxygen to itself and all other cells in the body determines the quality of the
contraction and relaxation phases of the heart and other roles of the cardio
respiratory system. The efficiency of this system or the level of cardio
respiratory endurance can be evaluated with respect to three functions:
cardiac output, ejection fraction, and oxygen extraction.
Cardiac output is the
amount of blood that flows from each ventricle, lower pumping chambers of the
heart, in one minute. There are two factors involved in cardiac output: heart
rate and stroke volume. The heart rate refers to the number of times the heart
beats per minute (bpm). The other function, stroke volume, is the amount of
blood pumped from each ventricle every time the heart beats. Stroke volume is
measured in millimeters (ml) per beat (1 ounce = 29.6 ml). When the heart rate
or number of beats per minute is multiplied by stroke volume the resulting
product (volume in ml per minute) is the cardiac output. The following equation
and data illustrates cardiac output:
Heart rate = 60
bpm; stroke volume = 75 ml/beat;
Cardiac Output =
Heart Rate x Stroke Volume
= 60 bpm x 75 ml/beat
= 4500 ml/minute
This example represents a
cardiac output of about 5 quarts of blood pumped through the body every minute,
which is a typical cardiac output for an adult at rest. During exercise the
demand for oxygen increases; therefore, the heart rate increases to produce a
greater amount of blood flow. An increase in heart rate is accompanied by an
increase in breathing rate, which places more stress on the body during
exercise. Because of the sensations that come with increased stress, during
exercise, the effect of exercise is perceived to be more intense as the demand
for oxygen increases. This is referred to as the perceived rate of exertion.
A Swedish exercise physiologist, Gunnar Borg, created the Borg scale to assist
exercisers on how to interpret how hard or intense they are exercising. The
scale is from 1 to 20 with 1 as the lowest level of perceived exertion and 20 as
the highest level. The use of this scale may be more comfortable than
repeatedly counting the heart rate, another method used to determine level of
intensity of exercise. Thus, there are two ways to determine level of exercise
intensity, both of which are based on the stress of the cardio respiratory
system. The difference is that with the Borg scale, the sense of feel and how
it is perceived is used, while the other scale, target heart rate, is based on
the number of times the heart beats per minute. In either case, as the
intensity increases the higher the value of indicators of the two methods used.
The ejection fraction
is determined by the percentage of blood in the ventricles, during diastole
(heart at rest) that is pumped out or ejected, when the ventricles contract.
The amount of blood that fills the ventricles during diastole is not always
completely ejected. The percentage of the total volume of blood in the
ventricle at the end of diastole that is subsequently ejected during contraction
is called the ejection fraction. Since there is a minimal amount of oxygen
needed during rest, the ejection fraction at rest is only about 50 percent.
However, during exercise, the ejection fraction can increase to 100 percent,
because when there is an increase in the need for oxygen in the muscles, the
ventricles contract more forcefully to eject more blood.
Another important factor, regarding the functions of the cardio respiratory system during exercise, is the amount of oxygen taken from the hemoglobin or red blood cells (a function that takes place in the capillaries of muscles). This process is referred to as oxygen extraction. Usually, all of the blood delivered to the cells via the arteries is not extracted in the capillaries. Therefore, oxygen is in the veins, which carry blood away from cells to pulmonary circulation, but it is less than the amount of oxygen in arterial blood, which is oxygen rich and moving toward cells. This means that the average person is able to load the blood with more oxygen in the lungs than his or her body is able to use at the cellular level. Thus, the inability to breathe fast enough to supply oxygen needed at any given moment is not the limiting factor in performance. The main limitation to exercise performance is the inability of the muscle to extract all of the oxygen available in the blood from the blood stream. Thus, improvements in the functions of the heart, lungs, blood vessels, and blood are dependent upon increase in the amount of oxygen extracted from the capillaries by the mitochondria (explained below) of each muscle fiber. This attribute may be improved by regular physical activity.
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The Role of Oxygen in the Body
Why is oxygen so important?
An Understanding of the functions of the cardio respiratory system in oxygen
delivery and extraction can help explain energy production in the cells,
particularly muscle cells. When a muscle contracts and exerts force, the energy
used to drive the contraction comes from ATP. The amount of work that a muscle
cell can do before it becomes fatigued depends on how quickly and efficiently a
muscle cell can produce ATP. While some ATP is stored in muscle cells, the
supply is limited. Therefore, muscle cells must produce more ATP in order to
continue working.
Muscle cells replenish the
ATP supply by using three distinct biochemical pathways, or separate chemical
reactions: the aerobic system, anaerobic glycolysis and the creatine phosphate
system. The word aerobic means with oxygen, and it refers to the aerobic energy
system; this system is predominately used by the body to produce ATP in all
cells. When adequate oxygen is delivered into the muscle cell to meet energy
production needs, it is dominant, such as when muscles are at rest or during low
intensity activity. Most cells, including muscle cells, contain structures
called mitochondria. The mitochondria (organelles) are the sites
of ATP production for aerobic energy. Thus, the aerobic energy production
capability of a muscle cell is directly proportional to the number of
mitochondria that are available to remove oxygen (oxygen extraction).
Another form of energy
production is referred to as an aerobic; it is the production of energy without
oxygen. However, most cells, such as those in the heart, brain, and other
organs, have little or no anaerobic capability. Therefore, these cells must be
continuously supplied with oxygen, or they will die. For example, if the
coronary artery (which supplies blood and oxygen to the heart muscle) becomes
blocked with a blood clot or a build-up of cholesterol deposits (plaque),
there will be a diminished flow of blood through that artery. This reduction in
flow of blood may lead to chest pain and ultimately to heart attack,
which is death of heart cells. The aerobic system may be thought of as the life
or activity sustaining energy system.
There are two systems that
are anaerobic: anaerobic glycolysis and the creatine phosphate system. These
are the primary sources of ATP during exercise, when an inadequate supply of
oxygen is available in cells to meet energy needs. As stated above, both of
these systems are called anaerobic because they produce ATP without the use of
oxygen. The word anaerobic stands for without oxygen. The anaerobic production
of ATP occurs inside the cell, but outside the mitochondria. These systems are
triggered into action when a muscle needs to generate force quickly. That is,
the muscle action that is needed to lift a heavy weight or perform some other
activity that doesn’t last long triggers anaerobic energy production.
These systems are not capable of producing ATP for periods longer than 10 to 120 seconds, but they are capable of producing very intense contractions. Energy needs greater than that supplied by anaerobic systems can last for long periods of time; the capability for high intensity is reduced or lost. This means that as a person reduces intensity he or she will be able to last longer, and as intensity is increased he or she will reach fatigue sooner. Intense exercises rely on the production of ATP from anaerobic energy systems (anaerobic glycolysis and creatine phosphate systems), while long lasting endurance exercises rely on the production of ATP from the aerobic energy system or oxygen system.
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The total capacity to consume
oxygen at the cellular level is referred to as maximal oxygen consumption or VO2max
This phrase represents an individual's maximum aerobic capacity, and it depends
on two factors: 1) cardiac output, the delivery of oxygen to the working muscle
by the blood and 2) oxygen extraction, the ability of oxygen to be removed from
the blood in the capillaries and used in the mitochondria to produce ATP.
Maximum oxygen consumption is reported as milliliters of Oxygen per minute (ml
of O /min) and milliliters of Oxygen per kilogram of body weight per minute
ml/kg/min. The following equation and data demonstrates the calculations for VO2 max
at rest and during exercise:
Resting
Heart rate =
60 bpm; stroke volume = 75 ml/beat;
Weight - 154
lb or 154 lb/2.2 lb/ kg = 70 kg;
O2 extraction
max = 6 ml O2/100 ml of blood;
VO2 =
(cardiac output max) x (oxygen extraction max)/ 70 kg.
= (60 bpm x
75 ml/beat) x (6 ml O2/100 ml of blood)/ 70 kg.
= (4500
ml/minute) x (.06 O2)/ 70 kg.
= 270
ml O2/min/ 70 kg.
= 3.9
ml/kg/min
During Maximal
Exercise
Heart rate =
185 bpm; stroke volume = 120 ml/beat;
Weight - 154
lb or 154 lb/2.2 lb/ kg = 70 kg;
O2 extraction
max = 15 ml O2/100 ml of blood;
VO2
= (cardiac output max x oxygen extraction max)/ 70 kg.
= (185 bpm x
120 ml/beat) x (15 ml O2/100 ml of blood)/ 70 kg.
= (22200
ml/minute) x (.15 O2)/ 70 kg.
= 3330
ml O2/min/ 70 kg.
= 47.6
ml/kg/min
While the example above
represents a hypothetical situation and conditions, it illustrates the
difference the body’s capacity to consume oxygen. People, who exercise
regularly, have a greater capacity for oxygen use than those who do not exercise
regularly. Therefore, their cardio respiratory system functions more
efficiently to produce a higher level of maximum oxygen consumption or VO2 max.
When the principles of
fitness training are applied to oxygen use, there are three controls used to
improve aerobic capacity or VO2max,. They are frequency,
intensity, and time (FIT). As these measures are increased,
an improvement in VO2 max is expected. For improvement through
aerobic exercise to occur, the frequency of exercise recommended is from 3 to 5
days per week; and the intensity should be based on the principle of
readiness, the level of intensity that an individual is capable of, which
represents 60 to 70 % of his or her best. Also, the frequency, intensity, and
amount of time spent exercising should satisfy the principles of progression
and overload, a gradual increase in frequency, intensity, and
duration of exercise as the body becomes accustomed to a higher level of
activity. People should start at a safe level of exercise and gradually
increase the frequency, intensity, and time of exercise, as the body functions
adapt. The principle of specificity refers toexercise that focus on
specific outcomes with respect to the nature of the activity
addressed. For example one’s VO2 is improved by aerobic activities;
therefore, this form of exercise should be selected as the specific type of
exercise needed to improve maximum oxygen consumption or VO2 max. When
these four principles are properly employed, continuous improvement can be
accomplished and the risk of injury is minimized. One of the primary causes of
injury is the failure to apply the principles of readiness, and the principle of
progressive overload.
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It is important to understand
the functions of the cardio respiratory system in order to understand how it
responds to fitness activities. Such knowledge requires an understanding of the
structure of the heart, blood flow through pulmonary and systemic circulation,
and how and where oxygen must be extracted from the blood to be used in the
synthesis of ATP or to produce aerobic energy.
When energy is produced, it
becomes apparent that it increases according to the level of intensity, which is
due to the bodily effects that make the rate of exertion perceivable. The Borg
scale was designed to facilitate the use of rate of perceived exertion during
exercise. The use of this scale improves the ability of persons exercising to
apply the principles of fitness. That is, when the level of exertion perceived
is high the level of intensity is high and may be reduced to put it at the
desired level. Also, the target heart rate approach may be used to measure
level of intensity of exercise.
Cardio respiratory endurance
is measured by VO2 max, which represents the maximum amount of oxygen
used by cells to produce energy or ATP. During aerobic exercise there are three
controls that may be manipulated to apply the principles of fitness training:
frequency of exercise, intensity of exercise, and time devoted to exercise
(FIT). These controls may also be utilized to prevent injury, which is the best
protection for injury.
One's maximum oxygen
consumption can be calculated. When it is calculated at rest and compared with
the increase during exercise, it becomes clear that the cardio respiratory
system has a tremendous capacity to transport and supply oxygen to the cells to
produce ATP. Many organs in the body require the production of ATP via the
aerobic system, so the ability of the body to transport sufficient quantities of
oxygen is an important indicator of fitness and the most beneficial effect of
exercise, which can be pursued.
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American College of Sports Medicine. 1990. The Recommended Quantity and Quality of Exercise for Developing and Maintaining Cardio Respiratory Muscular Fitness in Healthy Adults. Medicine and Science in Sports and Exercise 22:265-74.
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