Download ESCC 4 Cardiorespiratory System Function in the

Specialist Certification Program
The Endurance Events
Cardiorespiratory System Function
in the Endurance Events
Cardiovascular System Anatomy and Function
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The Heart. The heart is a muscular organ which pumps blood throughout the blood vessels by
repeated, rhythmic contractions. The term cardiac means related to the heart. The human heart
is principally composed of cardiac muscle and connective tissue. It weighs approximately 9 to
11 oz. in females and 11 to 12 oz. in males.
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Cardiac Anatomy

Cardiac Muscle. Cardiac muscle is an involuntary striated muscle tissue found
only in the heart and is responsible for the heart’s ability to pump blood.
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Chambers. The human heart has four chambers, two superior atria and two
inferior ventricles. The atria are the receiving chambers. The left ventricle and
the right ventricle act as pumps, taking in blood at low pressure and outflowing
blood at high pressure. Muscular contraction is used to pump the blood.
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The Pericardium. The heart is enclosed in a double-walled sac called the
pericardium. The superficial part of this sac is called the fibrous pericardium.
This sac protects the heart, anchors its surrounding structures, and prevents
overfilling of the heart with blood.
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The Outer Wall. The outer wall of the human heart is composed of three layers.
The outer layer is called the epicardium, or visceral pericardium since it is also
the inner wall of the pericardium. The middle layer is called the myocardium
and is composed of cardiac muscle which contracts. The inner layer is called the
endocardium and is in contact with the blood that the heart pumps. Also, it
merges with the inner lining (endothelium) of blood vessels and covers heart
valves
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Cardiac Function

The Ventricles as Pumps. The ventricles act as pumps, using muscular
contraction to pressure the blood out of heart. The left ventricle is of particular
note, since it pumps blood throughout the body and shows great adaptations to
training.
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Blood Pathways. The pathway of blood through the human heart consists of a
pulmonary circuit and a systemic circuit. Deoxygenated blood flows through the
heart in one direction, entering through the superior vena cava into the right
atrium and is pumped through the tricuspid valve into the right ventricle before
being pumped out through the pulmonary valve to the pulmonary arteries into
the lungs. It returns from the lungs through the pulmonary veins to the left
atrium where it is pumped through the mitral valve into the left ventricle before
leaving through the aortic valve to the aorta.
The Blood Vessels. The blood vessels tubular structures that contain and direct the flow of
blood throughout the body.
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Types of Blood Vessels

Arteries. Arteries carry blood away from the heart, delivering oxygenated and
nutrient laden blood to the body’s tissues.
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Veins. Veins carry blood to the heart, returning deoxygenated and nutrient
depleted blood for replenishment.
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Capillaries. Capillaries are small blood vessels which enable the actual exchange
of oxygen and other substances and chemicals between the blood and the
tissues. Capillaries comprise the interchange between arteries and veins. They
are only one cell thick, enabling effective diffusion of nutrients into adjacent
cells.
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Vasoconstriction and Vasodilation. Vasoconstriction is the narrowing and decrease in
cross sectional area of blood vessels. It is produced by contractions of the vascular
smooth muscle in the vessel walls. Vasodilation is a similarly produced effect in which
the blood vessels cross sectional area increases.
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The Endothelium. The endothelium is a thin layer of cells that lines the interior surface
of blood vessels, forming an interface between circulating blood and the rest of the
vessel wall. Capillaries consist of endothelium and little else. Permeability of the
endothelium is pivotal in the release of nutrients to the tissue. It is increased in
inflammation, which leads to most of the symptoms of inflammation (swelling, redness
and warmth).
The Blood
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Blood. Blood is a specialized bodily fluid in that delivers oxygen and other necessary
nutrients to the cells, and transports waste products away from those same cells. Blood
is primarily composed of blood cells suspended in a liquid called blood plasma.
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Blood Components

Plasma. Plasma constitutes approximately 55% of blood fluid and is itself
comprised of approximately 90 percent water.
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Blood Cells
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Red Blood Cells. The most abundant cells in blood are red blood cells.
These contain hemoglobin, an iron-containing protein, which facilitates
transportation of oxygen by reversibly binding to oxygen and greatly
increasing its solubility in blood.
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
White Blood Cells. White blood cells are involved in immune system
function, defending the body against both infectious disease and foreign
materials.
The Lungs
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The Lung. The lung is the organ of respiration, where the exchange of gases is made
within the body. Their principal function is to transport oxygen into the bloodstream,
and to release carbon dioxide from the bloodstream into the atmosphere. The lungs are
located in two cavities on either side of the heart. Though similar, the two lungs are not
identical. Both are separated into lobes by fissures, with three lobes on the right and
two on the left.
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Air Pathways. Air enters through the oral and nasal cavities and flows through the
pharynx, then the larynx, and into the trachea. From there air moves into a
progressively subdividing system of bronchi and bronchioles until it finally reaches the
alveoli where the gas exchange takes place. This anatomy is of special concern because
of the prevalence of upper respiratory infections in endurance athletes.
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Ventilation. The drawing in and expulsion of air is called ventilation. Ventilation is
largely driven by the muscular diaphragm at the bottom of the thorax. Contraction of
the diaphragm pulls the bottom of the cavity in which the lung is enclosed downward,
increasing volume and thus decreasing pressure, causing air to flow into the airways.
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Gas Exchange. This exchange of gases is accomplished in millions of tiny, thin-walled air
sacs called alveoli. The individual alveoli are rich in blood vessels. Deoxygenated blood
from the heart is pumped through the pulmonary artery to the lungs, where oxygen
diffuses into blood and is exchanged for carbon dioxide in the hemoglobin of the
erythrocytes. The oxygen-rich blood returns to the heart via the pulmonary veins to be
pumped back into systemic circulation.
Cardiorespiratory Parameters of Training Concern
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Heart Rate. Heart rate is the number of heartbeats per unit of time, typically expressed as
beats per minute (bpm). Heart rate increases as work intensities and oxygen demand increase,
so heart rate is an accurate indicator of work intensity.
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Resting Heart Rate. Resting heart rate is the number of heartbeats per unit of time when the
body is at rest, with no work being done. Resting heart rate is a good indicator of training state
or state of fatigue.

Maximum Heart Rate. Maximum heart rate is the highest heart rate value one is capable of
achieving in an effort to the point of exhaustion. This is a highly reliable value that remains
constant from day to day. It remains constant regardless of the athlete’s training state.
Maximum heart rate decreases slightly year to year, approximately one beat per year after 15
years of age.
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Steady State Heart Rate. Steady State Heart Rate is the heart rate achieved when the rate of
work is held constant at submaximal levels of exercise. Heart rate will increase fairly rapidly until
it plateaus at the steady state rate, the specific level needed to meet the circulatory demands at
that work rate. Steady state heart rate will change with subsequent increases in intensity,
normally requiring 1 to 2 minutes to regain steady state.
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Stroke Volume. Stroke volume is the amount of blood expelled from the heart with each beat.

Cardiac Output. Cardiac output is the total volume of blood expelled from the heart in a given
time. Cardiac output can be represented mathematically as the product of stroke volume and
heart rate. In the early stages of exercise, cardiac output increases due to an increase in both
heart rate and stroke volume. Once exercise reaches approximately 60-65% of maximum
capacity, stroke volume increases at a much slower rate. Further increases in cardiac output are
then due to increased heart rate to meet the demand.

avO2 Difference.
avO2 Difference is a shortened form of the term arteriovenus oxygen
difference. It is a measure of the difference in oxygen content in arterial blood and venous
blood, and is thus a measure of the efficiency of oxygen extraction.
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VO2Max. VO2Max is the maximal rate of oxygen consumption one is capable of achieving. It is
also commonly referred to as aerobic power.
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Hematocrit. Hematocrit is the ratio between blood plasma volume and blood cell mass.
Increases in hematocrit result in increases in blood viscosity.
Cardiorespiratory Adaptations to Training
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Heart Size. In response to training, the heart’s weight and volume increase.
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Stroke Volume. As a result of training, stroke volume increases at rest, submaximal exercise,
and maximal exercise, as a result of training. Much of this stroke volume increase results from
changes in the left ventricle.
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Left Ventricle Changes
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Chamber Size Increases. Because of an increased volume of blood in the heart,
specifically in the left ventricle, the size of the chamber increases in order to handle this
greater demand.
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Increases in Venous Return.
Increases in left ventricular chamber size result in
increased venous return, thus increasing the end-diastolic volume.
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Increased Fill. As a result of training, the left ventricle fills more completely during
diastole
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Thickening of the Ventricle Wall. Along with the increase in the size of the chamber,
the increased blood volume also demands a thicker wall. The strengthening of the heart
associated with this thickening is highly correlated to increased VO2 Max.
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Increased Elasticity. Training results in an increased elasticity of the muscle wall,
creating a stronger more forceful contraction. This more forceful contraction will leave
less blood in the left ventricle at the end of systole (end systolic volume) following
training.
Heart Rate Changes
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Lowered Resting Heart Rate. Training results in a lower resting heart rate. Untrained
subjects normally show heart rates between 60 to 80 beats per minute. Highly trained
runners may show resting heart rates that range from 28-48 beats per minute.
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Lower Heart Rates at Work. Training results in a decreased heart rate at any level of
work.
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Increased Parasympathetic Activity. Training increases parasympathetic activity in the
heart while decreasing sympathetic activity. This response to training can be easily
measured by taking heart rates at rest at the carotid or radial site. Since heart rate
reflects the amount of work performed, the heart must meet the increased demands of
the body when engaged in activity.
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Steady State Heart Rate Decreases. Training results in lower steady state heart rates at
any specific work rate.
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Heart Rate Recovery. As a result of training, heart rate returns to its normal resting
values following exercise faster than it does in an untrained state.
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Blood Changes
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Volume. As a result of training, blood volume increases. following intense levels of
training. This results from an increase in plasma volume of at least 10% accompanying
training and acclimatization to heat. This increase in plasma volume increases the speed
of blood flow and increases the rate of oxygen delivery.
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Composition. Training results in increased red blood cell levels. This increases the
oxygen carrying capacity of the blood.
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Blood Flow Changes. The vascular system can redistribute blood to areas with the greatest
needs receiving greater volumes of blood. Blood is redirected, by the sympathetic nervous
system, to those areas that are active during exercise. 15-20 % of cardiac output is directed
towards working muscles at rest but this distribution changes to 80-85% during exhaustive
exercise. This increase occurs due to the reduction of blood flow to the kidneys, liver, stomach,
and intestines.

Blood Pressure Responses. In endurance training, systolic pressure increases gradually,
increasing from 120 mmHg to 200 mmHg at exhaustion. Highly trained endurance runners have
reported 240-250 mmHg systolic pressures. This increased pressure is due to increased cardiac
output that accompanies improved work rates. Blood pressure determines how much fluid
leaves the capillaries and enters the tissues. Training induced increases in blood pressure
improves the cardiovascular delivery process.
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Capillarization Changes
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Increased Capillarization. There are ordinarily 2 to 4 capillaries feeding untrained ST
and FOG fibers. Substantial increases in capillary numbers occur in response to training,
as high as 9 per fiber. This increase in capillarization decreases diffusion distance for O2
as it moves from capillary blood into the working skeletal muscles.
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Improved Capillarization. The existing capillaries in trained muscles can dilate more and
increase blood flow into the muscle.
Increased Oxygen Extraction. Increased avO2 difference levels result from training. This
enhanced level of avO2 difference is related to the enzymatic and other biochemical changes
that occur within the muscles as a result of training.
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