Anatomy and Physiology – Neuromuscular Function

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Anatomy and Physiology – Neuromuscular Function

CRT04101 · Anatomy, Physiology and Pathology

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Anatomy and Physiology – Neuromuscular Function

What Is Neuromuscular Junction?

A motor neuron is responsible for causing a skeletal muscle to
contract, by stimulating it. The gap or space present between this
motor neuron and the skeletal muscle cell is called as a synapse. This
synapse, specifically between the skeletal muscle cell and motor
neuron is called neuromuscular junction or myoneural. Myo means
Muscle and Neural means Nerves. When an impulse travels between
this space, muscle contraction happens.
There are around 100-500 trillion such connections in the human
brain, between two nerves or nerves and glands. In this article we will
discuss only the neuromuscular junction.
Structure of Neuromuscular Junction
As we have read, a neuromuscular junction consists of a neuron and a
skeletal muscle cell. The neuron in the combination is referred to as
spinal motor neuron. The motor neurons, who originate from the
spinal cord, innervate the skeletal muscle fibers. The innervations
happens by very fine processes of the axon. The synapses are present
along these processes and are also known as motor endplate, because
of its specific structure.
The neuromuscular junction synapse has 3 characteristic features:
There are two membranes called the pre and post synaptic
membranes. There exists a distinct space between these membranes
and is known as Synaptic Cleft.
High density of small spherical vesicles is present, which contain
neurotransmitter substances.
A thickened post synaptic membrane is present, which has high
density of receptors that are responsible for binding the chemical
substances which transmit the signal from the pre synaptic neuron.
Functions of Neuromuscular Junction
Before going in detail, let us remember the broad action of this
junction. It is to act like a bridge between a neuron and muscle cell to

transmit the signals.

Motor Neuron—Synaptic Cleft—Skeletal Muscle Cell

Calcium makes an entry in the excited motor neuron, which in turn
causes exocytosis of the neurotransmitter. Which means the
neurotransmitter gets transported to the only place available – the
synaptic cleft. Acetylcholine is the neurotransmitter secreted by the
somatic motor neurons.
There are receptors of acetylcholine present in the skeletal muscle
cells. So this secreted acetylcholine then passes the cleft by diffusion
and bind with the receptors. They are like puzzle pieces which fit or
key which opens the door. This process opens an ion channel through
which sodium ions pass to the muscle cells. At that time potassium
ions diffuse out of muscle cells. However, the amount of Sodium ions
entering is higher than the number of potassium ions leaving. Once the
sodium ion reaches the muscle cell, it depolarizes, because it is a
positive ion. This causes the skeletal muscle cell membrane to get
excited and contract. This is referred to as Action Potential being
triggered.
The acetylcholine does not remain in the synaptic cleft of the
neuromuscular junction forever. This is to ensure that it does not cause
over contraction of the muscle or keep the muscle contracted for
longer than required. An enzyme called as Acetyl cholinesterase is
responsible in acting as a catalyst in breaking down the acetylcholine

present in the synaptic cleft. It gives rise to acetate and choline, which are then transported back to the synaptic cleft, where they are resynthesized. This is called as Active Reuptake.

Neuromuscular Junction Disorders ‗

Some of the disorders affecting the neuromuscular junction are
Myasthenia Gravis, Botulism, Eaton-Lambert syndrome etc. The
neuromuscular junction can also malfunction when exposed to certain
antibiotics, organophosphates which are type of insecticides, curare
which is a toxin derived from plants and gases used in chemical
warfare. Some of these things work by preventing the breakdown of
acetylcholine after the transmission of the nerve impulse. While some
of the disorders cause over activity of the muscles as described below:
person syndrome: Antibodies attack nerve cells – responsible for
muscle regulation – present in the brain and spinal cord and cause
them to be continuously stimulated. Due to this they become stiff.
Isaacs’s syndrome: In this the nerves keep sending impulses to the
muscles which causes them to be over stimulated and ultimately
stiffen. They also tend to twitch, due to which they find exercising
and normal activities difficult to perform.
Fuel for muscular activity.
Your body is your vehicle, so you have to keep your engine — your heart —
running when you work out.
That means fueling up your tank with the right foods and your radiator with
the right fluids, using with right amounts at the right times. The American
College of Sports Medicine says, ―Adequate food and fluid should be
consumed before, during, and after exercise to help maintain blood glucose
concentration during exercise, maximize exercise performance, and improve
recovery time. Athletes should be well hydrated before exercise and drink
enough fluid during and after exercise to balance fluid losses.‖
Not fueling up before you work out is like ―driving a car on empty,‖ said
Platt, an American Heart Association volunteer. You also won‘t have
enough energy to maximize your workout and you limit your ability to burn
calories.
Ideally, fuel up two hours before you exercise by:
Hydrating with water.
Eating healthy carbohydrates such as whole-grain cereals (with lowfat or skim milk), whole-wheat toast (without the fatty cream cheese),
low-fat or fat-free yogurt, whole grain pasta, brown rice, fruits and
vegetables.
Avoiding saturated fats and even a lot of healthy protein — because
these types of fuels digest slower in your stomach and take away
oxygen and energy-delivering blood from your muscles.
If you only have 5-10 minutes before you exercise, eat a piece of fruit such
as an apple or banana.
―The key is to consume easily digested carbohydrates, so you don’t feel
sluggish,‖
Whether you‘re a professional athlete who trains for several hours or you
have a low to moderate routine, keep your body hydrated with small,
frequent sips of water.
According to researchers don‘t need to eat during a workout that‘s an hour
or less. But, for longer, high intensity vigorous workouts, she recommends
eating 50-100 calories every half hour of carbohydrates such as raisins, an
energy bar or banana.
Fluids. Drink water, of course. Blend your water with 100% juice
such as orange juice which provides fluids, carbohydrates.
Carbohydrates. You burn a lot of carbohydrates — the main fuel for
your muscles — when you exercise. In the 20-60 minutes after your
workout, your muscles can store carbohydrates and protein as energy
and help in recovery.
Protein. Eat things with protein to help repair and grow your muscles.
It‘s important to realize that these are general guidelines. We have
different digestive systems and ―a lot depends on what kind of
workout you‘re doing,‖ Platt said.
So do what works best for you. Know that what you put in your body
(nutrition) is as important as you what you do with your body
(exercise). Both are crucial to keeping your engine performing at its
best.
How to Fuel Muscles during Exercise – Understanding the Importance of
Carbohydrates
Adopting a regular exercise routine is one of the best things that you can do
for your long-term health.
Exercise benefits all tissues in the body, and with each passing year research
continues to learn more about the benefits of frequent and consistent
movement. Over the course of 10 years of nutrition and fitness research
science, I‘ve developed a huge appreciation for the benefits of exercise, that
seem almost too numerous to count.
Simply stated, exercise benefits all organ systems in the human body,
including your heart, blood vessels, muscles, bones, ligaments, tendons,
immune system, intestines, liver, pancreas and brain. That‘s right, even
tissues that have nothing to do with performing exercise receive the benefit
of frequent activity. Understanding how to fuel muscle during exercise is the
first step in optimizing your individual athletic recovery program.
Exercise is a Beneficial Stress
Exercise is considered a ―stress‖ too many organ systems, but differs from
the negative stress of everyday life in that it stimulates the breakdown, repair
and growth of muscles, ligaments, tendons and bones in the process of
creating a stronger and more resilient body.
During exercise, muscles must perform two main tasks: Oxidize or ―burn‖
available fuel for energy. Contract in response to a rush of electrical signals
from the brain
By accomplishing both tasks simultaneously, the muscle performs work,
generating heat, waste products and the need for increased blood flow.
Here‘s a behind-the-scenes look at what fuels your muscles are using to
power you during your workouts.
Muscle Fuel during Exercise
The muscle is capable of burning multiple fuels during exercise, including
glucose (from carbohydrates), fatty acids (from fat) and amino acids (from
protein).
In the same way that a car stores fuel in a fuel tank, muscles have evolved
the ability to store glucose, fatty acids and amino acids on-board. All three
fuels are burned for energy in the mitochondria, organelles within muscle
cells that function much like a car engine.
Even though a car only has one engine, a single muscle cell often contains
hundreds of mitochondria in order to generate large amounts of energy
during exercise. In this way, the muscle is specifically designed to generate
massive amounts of energy on the fly.
Glucose is Stored as Glycogen
Glucose is stored within each muscle cell as glycogen. Glycogen is
specifically designed for quick-burning energy, and fast acting enzymes in
the muscle cell allow for easy access to this large reservoir of fuel.
Many people believe that carbohydrates are the enemy and should be
avoided at all costs. On the contrary – dietary carbohydrates contribute to
glycogen stores, literally fueling your muscle tissue.
Just make sure that your carbohydrates come from REAL sources, and not
from fake and refined products.
Fatty Acids are Stored as Triglyceride
Fatty acids are stored within muscle cells as triglycerides. Muscle
triglycerides are stored in a lipid droplet that can be accessed
set of enzymes, providing a secondary fuel source during exercise.
Amino Acids are Stored as Muscle Protein
Finally, amino acids are stored within the muscle tissue as muscle protein. If
a muscle cell were a car, the muscle protein is the metal frame of the car that
provides structure and rigidity. Think of muscle protein as the infrastructure
of the muscle tissue itself. Unlike glucose and fatty acids, there is no storage
tank for amino acids in the muscle tissue. The muscle itself is the storage
tank.
The Choice of Fuel Depends on Exercise Intensity
Even though all three muscle fuels are available for use during exercise, the
muscle is making moment-by-moment decisions on which fuel to burn,
depending mainly on the intensity and duration of exercise being performed.
At low intensities, fatty acids are the main fuel source and only small
amounts of glycogen are broken down. As the intensity of exercise
increases, larger amounts of glycogen are broken down and burned for
energy, making glucose the predominant fuel source. As you can see in the
graph below, as the intensity of exercise increases, the dependence on
carbohydrate goes up and the dependence on fatty acids goes down.
You may notice that only carbohydrate and fat are fuel sources shown in the
above graph. That‘s because amino acids are the lowest priority fuel, given
that it is the infrastructure of the muscle tissue itself. In order to preserve
muscle mass, the muscle will burn glucose and fatty acids before resorting to
amino acids.
Muscle Micro trauma
Even though amino acids from muscle protein are the last choice for fuel
during exercise, microscopic tears result from repeated muscle contractions,
called micro trauma. These microscopic tears are one of the signals that the
muscle requires in order to repair during rest.
Think of micro trauma as the repeated wear-and-tear that your car
experiences from driving long distances. In the same way that you replace
damaged engine parts with newer and more efficient technology, micro
trauma to muscle protein requires repair immediately following exercise.
Lucky for you, when muscle tissue repairs itself, the muscle will
overcompensate by creating stronger, more resilient muscle protein so that
the risk of repeated damage is reduced.
Overcompensation is exactly why muscles get stronger over time. Enzymes
that partake in the muscle repair process ―overreact‖ to micro trauma in
anticipation of future damage.
Amino acids from dietary protein are used as the building blocks for new
muscle protein. This is why protein is often considered an essential
component of your post-workout recovery meal.
Muscle is the largest type of tissue in your body, and is extremely malleable
because it responds to the type, duration and intensity of exercise that you
perform. Frequently exercised muscle tissue is in a constant state of
remodeling, leading to increases in endurance, strength, flexibility and
power.
The next time you perform a workout, keep in mind that your muscle is
performing a number of tasks at the same time, including the following:
Choosing between glucose and fatty acids for energy
Protecting muscle protein from being used as a fuel source
Contracting repeatedly, hundreds to thousands of times in a single
exercise session
Role of oxygen- physical training, oxygen debt, second wind, vital
capacity.
The day-to-day variability in oxygen consumption in most physical actions
is about 5%, and differences of 10% of this percentage among individuals
can be expected. Energy costs vary greatly in different sports; eg, for a 150-
lb player, 4.4 kcal/minute in archery, 9.1 kcal/minute in field hockey, 13.3
kcal/minute in judo, and 18.6 kcal/minute in squash.
Energy output also varies in the same sport depending on such factors as
intensity of competition, neuromuscular skill level, position demands,
performance level, age, body type, atmospheric conditions, and field
conditions. In exercise physiology, however, it has been shown to be valid to
measure energy expenditure of muscle tissue in terms of oxygen
consumption in liters/minute but not valid to convert such data into energy
units of watts or kilocalories/minute.
Metabolic capacity, maximum oxygen-intake capacity, and maximum
oxygen-debt capacity are the current priority concerns of exercise
physiologists.
Metabolic capacity determines the amount of activity possible
for approximately 2-3 hours through the maximum quantity of
energy-yielding substrates available from body reserves during
maximum aerobic demands.
Maximum oxygen-intake capacity (aerobic power) determines
the amount of activity possible for approximately 15-30 minutes
through coordinated circulatory and respiratory adjustments
producing the maximum amount of tissue oxygen.
Maximum oxygen-debt capacity (anaerobic power) determines the
amount of activity possible with all-out effort for approximately 50 seconds
through anaerobic release mechanisms.
When muscular effort must be prolonged longer than a minute, performance
becomes increasingly dependent upon the demands of holistic homeostasis
and not just that of active tissues. Basically, this involves oxygen supply,
carbon dioxide removal, heat balance, and the replenishment of nutrients.
Metabolism
To maintain health, stored resources (potential energy) must be kept in
balance with power expenditures (kinetic energy). While carbohydrate and
fat are normally oxidized almost completely in the human body, protein is
not. Protein derivatives of uric acid, urea, and creatinine are excreted in the
urine. In addition, not all food ingested is absorbed; that is, 97% of
carbohydrate, 95% of fat, and 92% of protein ingested is absorbed, and these
numbers do not consider the "coarseness" of foodstuffs such as coarse corn
meal or roughly ground whole grains.
Metabolic Rate. Metabolic rate is directly proportional to gross body
weight. Such factors as lean body mass, age, diet, sex, height, surface area,
and race do not have a significant influence on metabolic rate during
physical activity. The greater the energy demands, the higher the
requirement for oxygen consumption. Total energy is the result of the basal
(waking state) metabolic rate plus the energy necessary for work. This offers
a ratio that can be used as an index to measure exercise intensity and
performance efficiency. In a given period of time, energy output intensity is
directly related to mechanical performance, measured by oxygen
consumption in a specified period. In this sense, oxygen consumption can be
considered a reflection of metabolic power.
Metabolic Capacity. Metabolic capacity is directly related to performance
capacity, reflecting the quantity of energy-yielding nutrients available (2-3
hours) from body reserves under aerobic conditions. Thus, one's maximum
aerobic power and metabolic capacity are closely related, yet there are many
individual differences. Besides metabolic capacity, other indices may be
used such as those of glycogen storage, cardiac output, and water-balance

efficiency.

Aerobic Power

To produce necessary energy, the body uses an aerobic (oxygen) pathway
and an anaerobic (no oxygen) pathway. To maintain life, the primary factor
is the continuous and adequate flow of oxygen.
Restricted oxygen flow quickly manifests in function deterioration as seen
clinically following infarcts and strokes, underscoring why so much
emphasis is placed on oxygen demands during physical, psychological, and
environmental stress. Life signs and the degree of life are routinely
evaluated from detectable arterial pulsation, breathing quantity and quality
and rhythm, temperature, and reflexes -all of which are related to oxygen
flow.
When oxygen demands exceed supply (oxygen debt) during and following
prolonged exertion, lactic acid accumulates within muscle tissue and
encourages fatigue. The greater the exercise intensity, the greater the lactic
acid accumulation. Following maximum exercise, it may take an hour or
longer to attain resting levels. Oxygen debt must be repaid rapidly such as

through hyperpnoea.

Anaerobic Power

Short bursts of effort primarily using explosive strength requiring less than
120 seconds are considered anaerobic activities. Because blood, circulation,
respiration, and all the other factors contributing to human function during
effort cannot be produced on a moment's notice, nature provides certain
limited anaerobic mechanisms to meet the metabolic demands of active
cells. Even with minimal work intensity, there is a period of oxygen
deficiency that disturbs homeostasis and sets in motion a call for restoration
at a higher metabolic level.
Both aerobic and anaerobic mechanisms determine an individual's
performance capacity, but anaerobic activity is maintained only for a short
time. An anaerobic state exists when oxygen is not used to produce energy
and when glucose and glycogen reserves are used. The greater the intensity
of the effort, the greater the anaerobic energy contribution. This can be
measured by the amount of oxygen intake during the recovery period,
usually attaining its peak (maximum oxygen debt) in about 50 seconds after
intense exercise begins. If performance demands are great enough to exceed
maximum oxygen transport capabilities, performance proceeds only until
anaerobic energy stores become exhausted.
An index of work capacity is mechanical power of an anaerobic nature.
Common tests are (1) running staircases, as the energy requirement for
maintaining speed in running a specified distance depends on mechanical
performance during the period and (2) using a bicycle ergometer, where the
mechanical work is calculated by recording through a photoelectric circuit
the number of wheel revolutions. Activity examples also include weight
lifting, throwing, 100-yard dash, 100-meter freestyle swim, a basketball fast

break, or running bases in baseball.

Interval Training

Interval training was developed because of problems associated with lactic
acid buildup. Workouts interspersed with rest periods diminish a large
accumulation of lactic acid and delay fatigue. Sessions require strict
administration. It consists of repetitive efforts in which distance is set and
pace is timed with established intervals for recovery between efforts. Long
runs increase aerobic capacity, and fast, short run increase anaerobic power
and strength. As conditioning progresses, the time is shortened, the number
of runs is increased, and the number of rest intervals is decreased.
The interval pattern of effort and rest for a specific amount of work and time
critically determines the rise of excessive lactate levels, which, as previously
explained, is a major cause of fatigue. In long-term events, it is important for
an individual to keep high energy demands met by anti lactic acid reserves
and try to tactically have the competition exceed their reserves.
Pace and recovery time is usually determined by pulse rate rather than time.
Some authorities state that heart rate must be 60% of the available range
from rest to the maximum attainable (eg, 140+ beats/minute during running)
to develop a rate decrease of the working heart. Thus, they claim, an athlete's
pulse below 140/minute indicates a need for a faster run or swim. Once
pulse rate decreases to a desired level, rest intervals are ended. Such

conclusions, however, fail to consider many unique individual factors.

The Pulmonary Apparatus

The level of oxygen saturation greatly determines the oxygen-carrying
capacity of the blood, and oxygen saturation depends on factors determining
the quality and quantity of oxygen diffusion in the lungs. These factors
include
(1) the quality of pulmonary blood flow and neuromuscular mechanisms,
(2) the lung area available for the diffusing process,
(3) the time duration in which blood receives alveolar-capillary exposure,
(4) the thickness of the alveolar-capillary membrane,
(5) the alveolar air and pulmonary capillaries oxygen pressure differential,
and
(6) respiratory frequency, which is often linked in the athlete with the
rhythm of movement.
It therefore becomes apparent that the quality of oxygen transport is
contingent on the blood, the cardiovascular system, and the pulmonaryrespiratory system.
Ventilation. Lung function is evaluated by physiologists by measuring
pulmonary residual volume and vital capacity -the components of total lung
volume. As an index to breathing capacity, vital capacity is calculated from
the maximum amount of air exhaled after a maximum inhalation. About
20% of vital capacity is used during rest. About 70% might be used during
prolonged exercise. Up to a quarter of external ventilation is "wasted" in
pulmonary "dead space" due to the incomplete mixing of alveolar and
airway air, enhanced by an athlete's or a laborer's typically diminished
respiratory rate.
Ventilation efficiency is assisted as tidal volume increases with decreased
respiratory frequency for given total ventilation. More commonly,
ventilation efficiency is judged by the quantity of air inhaled or exhaled in
relation to the amount of oxygen absorbed. Such measurements must take
into consideration varying atmospheric conditions and individual metabolic
needs. Because adequate oxygen is essential for life, both oxygen demands
and oxygen consumption must be considered.
Lactic Formation and "Choked" Performance. It has been described
that during heavy exercise lactic acid accumulates within muscle as a result
of oxygen demands exceeding oxygen supply. Choking of performance
because of excessive competition or poor pacing may lead to early anaerobic
demands on metabolism. The result is lactate accumulation, witnessed as a
premature distressing hyperventilation. Local muscle weakness may also
induce premature breathlessness.
Hyperventilation from premature lactate accumulation can cause a person to
exceed normal ventilation adjustments where oxygen delivered to the
circulation is less than the corresponding demand for oxygen consumption.
It is thus important for an athlete to avoid lactate accumulation until late in
activity. If local muscle weakness is the cause, the situation can be corrected
by strengthening exercises so the athlete can operate nearer aerobic power
before lactate accumulates sufficiently. Marathon runners usually operate
just under their lactate threshold until the final sprint.
Second Wind. A "second wind" is considered an opposite reaction to that
found with choked performance. While early lactate accumulation may be
the result of physiologic forces (eg, cardio respiratory maladjustment), with
prolonged activity systemic blood pressure rises, movement pace is steadied,
ventilation diminishes, and the respiratory muscles become "warmed-up",
which reduces respiratory resistance and awareness of breathing, and the
level of circulating lactate is lowered. Other mechanisms may also be
involved.
Diffusing Capacity. Many well-conditioned athletes, especially swimmers
and other endurance-related participants, exhibit a large pulmonary diffusing
capacity (larger pulmonary surface) that enhances oxygen transfer. These
athletes also exhibit an increased ratio of oxygen intake to lung ventilation
per minute, which decreases as exhaustion approaches. However, even with
maximum effort, the equilibrium of pulmonary gases between the blood
stream and alveolar spaces is fairly complete. Thus, a gain in diffusing
capacity offers little benefit except for swimmers who deliberately hold their
breath or for athletes performing at high altitudes.
Carbon-Dioxide Homeostasis. Both low and high levels of carbon dioxide
affect normal tissue function. Excessive carbon dioxide elimination may be
encountered in high altitudes, witnessed by intermittent ventilation and
symptoms of mountain sickness; ie, dyspnea, headache, blood pressure and
pulse rate changes, and neurologic disorders due to maladjustment to
reduced oxygen pressure at high altitudes. Accumulation of carbon dioxide
is unusual except for the scuba diver due to the increased rate of carbon

dioxide production, the decreased maximum voluntary ventilation, the added external dead weight, and the possible inefficiency of the carbon dioxideabsorbing canisters.

The Circulatory System

Blood transports oxygen, energy substrates, and metabolic wastes. It also
serves a vital role in temperature regulation. Reduced blood volume, reduced
red cells, and reduced hemoglobin lower the body's capacity for aerobic
activity. Each tissue has a range of functional response with definite limits of
adaptation. In this sense, blood oxygen transport capability is limited by its
capacity to carry oxygen (ie, hemoglobin content and oxygen saturation).
An individual's pulmonary blood flow, lung diffusing capacity, rate of
oxygen removal, and total hemoglobin all have a close relationship with
maximum oxygen intake. Total hemoglobin determines the potential arterial
capacity to transport oxygen. For example, low hemoglobin levels in an
athlete are often attributed to increased cell destruction, as shown by
increases in circulating haptoglobins from increased rates in blood flow or
extrinsic trauma (eg, runner's feet, boxer's abdomen). Dietary habits are
more significant than the minute amounts of iron lost in perspiration.
Cardiac Output. Blood oxygen transport also depends on cardiac output.
While evaluation of cardiac output during exertion is helpful in diagnosis,
stroke volume is difficult to determine directly. Cardiac output increases
with work intensity and is directly related to the quantity of oxygen intake:
maximum heart output parallels maximum oxygen intake. Such factors as
heat exposure and/or dehydration influence stroke volume and change the
relationship between heart rate and stroke volume that alters the relationship
between oxygen consumption and heart rate.
Cardiac output effectiveness is also determined
distribution among active muscles, viscera, and skin. The maximum limits of
stroke volume are determined by the type of exercise and body posture. For
example, in comparison to a runner or swimmer who uses most of the body,
a cyclist, in not using his upper extremities for propulsion, often pools a
large amount of blood within upper extremity veins. The consequence of this
is a reduced stroke volume in the cyclist.
Oxygen Pulse. During exertion, cardiac stroke volume increases and the
active cells take more oxygen from arterial blood. Both of these factors
increase oxygen delivery to cells. The term "oxygen pulse" refers to the
quantity of oxygen removed from the blood during each pulse. It is
measured in a specified period by dividing oxygen intake by heart rate.
Oxygen pulse increases during exertion, reaching its typical maximum of
from 11 to 17 ml at about 135 pulses per minute and decreasing after further
cardiac acceleration.
Heart Rate. Heart rate is closely correlated with maximum oxygen intake.
Typically, heart rate is parallel with performance intensity, but maximum
cardiac rate decreases with advancing age. There is a linear relationship
between heart rate and metabolic rate. Due to the wide variance in individual
balance between sympathetic and vagal drives to the cardiac pacemaker, the
resting heart rate of the endurance-trained athlete may reach lows of 30 per
minute. The maximum sustained heart rate during competition is about 185-
195 per minute or less. In activities of high stress and isometric exertion (eg,
skiing), peak heart rates of 250 per minute or more may be briefly
encountered.
Blood and Pulse Pressures. Blood pressure and pulse pressure also have a
close relationship with maximum oxygen intake. To meet oxygen demands
during prolonged exertion, the blood quantity in the muscles and the blood
flow within the lungs must be increased. By increasing the force of heart
muscle contraction, systolic blood pressure is raised as heart rate increases.
This increase is minimized in the well-trained athlete. This is attributed to
decreased peripheral resistance because of vasodilatation.
Pulse pressure, the difference between systolic and diastolic pressures, offers
an index to the efficiency of cardiac contraction and stroke volume.
Difficulties in the exchange of oxygen and carbon dioxide in active tissues
are rarely anticipated except in specific types of events. For example, an
overland cyclist may complain of pain and weakness in leg muscles during
hill ascents. This is apparently caused by local circulatory obstruction
resulting from vigorous quadriceps contractions. However, if activity can be
continued in spite of the pain, increased systemic blood pressure tends to
overcome the local vascular occlusion. This phenomenon is thought to be a
manifestation of the heart failing to develop an immediate and adequate

increase in blood pressure.

EXCLUSION CRITERIA FOR POTENTIALLY HARMFUL

ACTIVITY

While the scope of this paper cannot include all possible types of
dysfunction and pathologic structural disorders that would exclude an
individual from a specific activity, certain guidelines can be used to support
the physician's decision. The base for discussion here is the athlete, but a
person involved in strenuous physical labor would be just as appropriate.
Whatever the circumstances and pressures, no athlete should be
allowed to risk permanent injury. An athlete is either capable
from a health standpoint or not.
An athlete should be allowed to participate in the sport of his or
her choice if practice and competition can be without danger to self
or squad.
As all sports contain some risk, one sport or level of
competition (intramural vs. varsity) should not be considered
safer than another in itself. Impartiality must be constantly held.
However, the risk of a disability must be differentiated between
one sport or position, and the demands involved, and another
sport or position. For instance, ankle weakness may be viewed
differently in a running sport than in polo.
Before any screening, evaluation, diagnostic, or therapeutic
procedure is used, informed consent must be given.
A physician wins no friends when he must disqualify a motivated athlete or
a willing worker who depends on a particular job for his livelihood. Yet, any
acute or chronic disease process is reason for disqualification until health is
attained. A weakened player is not the equal of a healthy player, and the risk

of injury is far higher.

Acquired Disorders

Self-limiting infections require only temporary exclusion. While competition
during mild coryza may be permitted, fever is a strict reason for exclusion. A
low-grade tonsillitis or dental sepsis may result in poor performance and
greater risk. As a guide, the "step test" is often used for signaling if an
athlete is ready to return to active competition after an infection.
The player steps on and off an 18-inch platform at a rate of 30 times per
minute. The examiner records the player's pulse rate at 30 seconds, 1 minute,
2 minutes, and 3 minutes after the exercise. The following formula is then
applied:
Duration of exercise in seconds x 100/2 x sum of any 3 pulse counts
during recovery
The higher the index, the better the person's status. An athlete is not ready to
return to sports activity if the index is 65 or less, according to general
opinion. However, both qualification and disqualification are serious matters
that cannot be left to the conclusions of one or two tests. Physicians are held
accountable to their clinical judgments, not to test results.
Surgical and Congenital Disorders
Gross structural deformity, malfunction, traumatic or surgical loss of a major
part, a history of extensive pathology, three concussions resulting in
unconsciousness of 1 minute or longer, active hernia, or recurring injury of a
part are considered by most authorities to be disqualifying in contact sports
regardless of body compensation and even if approved by player, parents,
family doctor, specialist, psychologist, and coach. The risks are far too great.
At the same time, a noncontact sport may be approved. The possibility of a
change in team position can also be considered.
The postoperative athlete must be evaluated not as the average postoperative
patient who is to return to a sedentary life-style but as one who will be
subjected to forces far above those normally encountered. The extent of
pathology and its complications, the extent of surgery and complications,
and the type of incision are all variables that must be weighed.
In contact sports, a single eye, a limb loss, an un descended testis, or a
unilateral renal dysfunction or malformation are usually considered reasons
for automatic disqualification regardless of the outward health status of the
functioning part. No athletic activity is worth the consequences of possible
injury to a healthy part, although this point is controversial among many.
Concern over a single ovary is not as great as the organ is well protected.
Such conditions as recurring gleno humeral dislocations, acromio clavicular
separations, and knee instability are usually considered disqualifying. Even
with successful surgical repair, wires can break, screws can loosen, and
plates can slide from severe stress. The physician's objective must be to
avoid the risk of permanent impairment.
Non disabling congenital defects are judged relative to the risk involved. For
example, non symptomatic spondylolis thesis without spin a bifida features
would not bar participation in a contact sport, but severe low-back
symptoms may be reasons for disqualification even if overt signs are not

evident.

Respiratory Considerations

Asthma must be judged on its degree and the sport involved, and some
asthmatics receive relief of their bronchi spasm during exercise. No
asthmatic dyspnea is usually related in the healthy to effort expended during
vigorous exercise, and it may be especially noticeable in cold weather. Mild,
occasional hemoptysis is normal with some athletes after strong exertion, but

profuse or commonly bloody sputum demands a full investigation.

Cardiovascular Considerations

The largest percentage of non traumatic deaths in sports can be attributed to
ischemic heart disease, unsuspected preexisting cardiovascular anomalies,
and infections having myocarditis in their repertoire. Occasionally, some
conditions are first discovered by the sports physician such as aortic
coarctation, asymptomatic atrial septal defects, dextrocardia, and rarely
mitral insufficiency.
A finding of abnormal thrill, hum, pulse, blood pressure, murmur, or
arrhythmia should be followed by simple exercise tests, and then
reevaluated. Transient palpitations, tachycardia, cardiac flutters, and
dizziness often cause diagnostic difficulties, and many ectopic arrhythmias
disappear when the heart rate exceeds 140. Premature ventricular
contractions are frequently noted by a team physician. These are often of
minor concern and associated with emotional causes, gastrointestinal

disturbances, and certain drugs (eg, caffeine).

Heart Disorders

A review of the literature reveals that there are wide differences in specific
disqualifying criteria. Paroxysmal auricular tachycardia is strictly
disqualifying for all competitive sports owing to the possibility of
unpredictable fainting during stressful activity. This does not include the
commonly witnessed psychogenic sinus tachycardia seen before
competition. Many physicians feel that any significant heart enlargement is
the basis for automatic sports exclusion. Compensated or repaired congenital
cardiovascular defects must be evaluated on an individual basis according to
cardiac reserve, and then only if a written clearance is obtained from the
attending cardiologist.
An abnormality within the cardiovascular system of a youth should not
cause automatic exclusion from sports. The concept of the need for a strictly
normal heart has been proven a fallacy. Records show a champion swimmer
with cyanotic heart disease, a famous long-distance runner who had a large
aortic aneurysm, an U.S. Olympic skier who participated with a piece of
shrapnel imbedded between the pericardium and the pulmonary artery, and
many similar situations. The goal is to recognize a disorder, evaluate it, and
establish the necessary guidelines to decrease risk and prevent serious

complications.

Blood Pressure

In healthy athletes, blood pressure will be found in a wide range of short
duration. A systolic pressure of 140+ constantly held is considered
abnormal, while pressures of short duration in youth of 150 and college
students of 220 are sometimes recorded. Abnormal levels in the healthy
return quickly within a normal range with relaxation. Of greater concern is a
rise in diastolic pressure. Many authorities believe that a resting pressure
over 88 points to kidney disease, a reason for disqualification. Boxing
examiners have recorded pressures of 65/40, indicating that hypotension

requires a redefinition in athletics.

Renal Disorders

During vigorous physical activity, five problems are commonly associated
with kidney function: dehydration, athletic pseudo nephritis,
hemoglobinuria, ephroptosis, and trauma.
Dehydration
Losses of up to 21% of plasma water have been demonstrated after 4 hours
of running. During high temperatures and humidity, it is virtually impossible
during prolonged exercise to replace fluids from sweat loss, even though it is
important to try to keep pace. From 200-300 ml of fluid are suggested for
every 15 minutes of strenuous activity. Athletes presenting symptoms of
chronic dehydration (eg, fatigue, decreased sweating, high core temperature)
require several quarts of fluid each day despite a lack of thirst.
Sodium depletion, often accompanying dehydration, is rarely a problem in
temperate climates under normal exercise conditions. It more often arises in
very hot climates, with indoor sports, and where restrictive clothing causes
increased perspiration. Typical features are thirst, headache, cramps, nausea,
apathy, anorexia, sleepiness, postural giddiness, peripheral circulatory
failure, and falling blood pressure. When ambient temperatures are known to
be high, a slow-release sodium supplementation is sometimes used in
maintaining electrolyte balance. Many authorities are against its use,
however.
Effect of exercise and training on cardiovascular system.
Effect on Heart Rate:
Exercise uses up a lot of energy, which the cells derive from oxidizing
glucose. Both glucose and oxygen have to be delivered by the blood. This
means that the heart has to work harder to pump more blood through the
body. This means it has to beat faster in order to achieve a higher
throughput, as described by this equation:
Heart rate for a human being at rest is about 70 beats/min. During vigorous
exercise, heart rate can increase dramatically (the rule of thumb given for
maximal heart rate is 220 minus your age). This will result in an increase in
blood flow.
The circulatory system responds to an increased need for blood by adjusting
the width of the blood vessels, primarily the arterioles and venules. The
dependence of vessel resistance on the radius of the tube is described by
Poiseuille's law and is described in detail in the exhibit,
As a complete system, the amount of blood that flows through the
circulatory system is in terms of the pressure difference between the arteries
and the veins times the quantity referred to as the total peripheral resistance.
But what about at the local level? How much blood flows through an
individual blood vessel? What are the quantities that affect the rate of blood
flow? This exhibit discusses a physical relation known as Poiseuille's Law
which partially answers this question.
Poiseuille's Law relates the rate at which blood flows through a small blood
vessel (Q) with the difference in blood pressure at the two ends (P), the
radius (a) and the length (L) of the artery, and the viscosity (n) of the blood.
The law is an algebraic equation,
From the formula given there, we see that blood flow depends very
sensitively on the width of the blood vessels, so that changing the radius
slightly has a large impact on the flow of blood.
The circulatory system exploits this property rather nicely; by constricting
blood flow the organs that need less oxygen during exercise and widening
the arterioles to the organs which need more. For instance, the brain may use
up to 30% of total blood flow while you're doing your homework, but when
you're at the gym less than 10% of total blood flow goes through it. On the
other hand, muscles use less than 10% of blood flow when at rest, but can
take up to 50% of it when they're working. This regulation is an essential
mechanism for delivering oxygen and glucose to the tissues that need it
most.
The cardiovascular system serves five important functions during
exercise:
Delivers oxygen to working muscles
Oxygenates blood by returning it to the lungs
Transports heat (a by-product of activity) from the core to the skin
Delivers nutrients and fuel to active tissues
Transports hormones
Exercise places an increased demand on the cardiovascular system.
Oxygen demand by the muscles increases sharply. Metabolic processes
speed up and more waste is created. More nutrients are used and body
temperature rises. To perform as efficiently as possible the cardiovascular
system must regulate these changes and meet the body‘s increasing
demands.
Below we will examine the acute or immediate response to exercise and
also the long-term adaptations that take place in the cardiovascular system
with repeated exercise. The most important aspects of the cardiovascular
system to examine include:
Heart rate
Stroke volume
Cardiac output
Blood flow
Blood pressure
Blood

Immediate Response of the Cardiovascular System to Exercise

Heart Rate

Resting heart rate averages 60 to 80 beats/min in healthy adults. In
sedentary, middle aged individuals it may be as high as 100 beats/min. In
elite endurance athletes heart rates as low as 28 to 40 beats/min have been
recorded.
Before exercise even begins heart rate increases in anticipation. This is
known as the anticipatory response. It is mediated through the releases
of a neurotransmitters called epinephrine and nor epinephrine also
known as adrenaline and nor adrenaline.
After the initial anticipatory response, heart rate increases in direct
proportion to exercise intensity until a maximum heart rate is reached.
Maximum heart rate is estimated with the formula 220-age. But this is
only an estimation, and not particularly accurate. The only direct method
for determining maximum heart rate is to exercise at increasing intensities
until a plateau in heart rate is found despite the increasing work rate.
Although heart rate increases rapidly with the onset of activity, providing
exercise intensity remains constant, heart rate will level off. This is
known as steady-state heart rate where the demands of the active tissues
can be adequately met by the cardiovascular system. However, there is an
exception to this
During prolonged steady-state exercise, particularly in a hot climate, a
steady-state heart rate will gradually increase. This phenomenon is known
as cardiac drift and is thought to occur due to increasing body

temperature.

Stroke Volume

Stroke volume is the amount of blood ejected per beat from left ventricle
and measured in ml/beat.
Stroke volume increases proportionally with exercise intensity. In
untrained individuals stroke volume at rest it averages 50-70ml/beat
increasing up to 110-130ml/beat beat during intense, physical activity. In
elite athletes resting stroke volume averages 90-110ml/beat increasing to
as much as 150-220ml/beat.
Stroke volume may increase only up to 40-60% of maximal capacity after
which it plateaus. Beyond this relative exercise intensity, stroke volume
remains unchanged right up until the point of exhaustion. But this is not
conclusive and other studies suggest stroke volume continues to rise until
the pint of exhaustion.
Interestingly, swimmers see a smaller increase in stroke volume compared
to runners or cyclists for example. It is believed that the supine position
prevents blood from pooling in the lower extremities enhancing venous
return.
Why does stroke volume increase with the onset of exercise? One
explanation is that the left ventricle fills more completely, stretching it
further, with the elastic recoil producing a more forceful contraction. This
is known as the Frank-Starling mechanism. Other contributing factors
include increased contractility of the ventricles and reduced peripheral

resistance due to greater vasodilatation of the blood vessels.

Cardiac Output

Cardiac output is the amount of blood pumped by the heart in 1 minute
measured in L/min. It is a product of stroke volume and heart rate (SV x
HR). If either hearts rate or stroke volume increase, or both, cardiac
output increases also.
Cardiac output increases proportionally with exercise intensity – which is
predictable from understanding the response of heart rate and stroke
volume to activity. At rest the cardiac output is about 5L/min. During

intense exercise this can increase to 20-40L/min.

Blood Flow

The vascular system can redistribute blood to those tissues with the
greatest immediate demand and away from areas that have less demand
for oxygen.
At rest 15-20% of circulating blood supplies skeletal muscle. During
vigorous exercise this increases to 80-85% of cardiac output. Blood is
shunted away from major organs such as the kidneys, liver, stomach and
intestines. It is then redirected to the skin to promote heat loss .
Athletes are often advised not to eat several hours before training or
competition. This is advice worth adhering to, as food in the stomach will
lead to competition for blood flow between the digestive system and
muscles. It has been shown that gastrointestinal blood flow during
exercise shortly after a meal is greater compared to exercising on an

empty stomach .

Blood Pressure

At rest, a typical systolic blood pressure in a healthy individual ranges
from 110-140mmHg and 60-90mm hemotocrit .Hg for diastolic blood
pressure.
During exercise systolic pressure, the pressure during contraction of the
heart (known as systole) can increase to over 200mmHg and levels as
high as 250mmHg have been reported in highly trained, healthy athletes.
Diastolic pressure on the other hand remains relatively unchanged
regardless of exercise intensity. In fact an increase of more than 15 mm
Hg as exercise intensity increases can indicate coronary heart disease and
is used as marker for ceasing an exercise tolerance test.
Both systolic and diastolic blood pressure can rise to high, albeit brief,
levels during resistance exercise. Values of 480/350mmHg (9) have been
reported to coincide with a Valsalva manoeuvre – i.e. trying to exhale
against a closed mouth, nose and glottis.
Blood
During resting conditions the oxygen content of blood varies from about
20ml of oxygen per 100ml of arterial blood to 14ml of oxygen per 100ml
of venous blood (2). The difference in oxygen content of arterial and
venous blood is known as a-vO2 difference.
As exercise intensity increase the a-vO2 difference increase also and at
maximal exertion the difference between arterial and venous blood
oxygen concentration can be three times that at a resting level.
Blood plasma volume decreases with the onset of exercise. The increase
in blood pressure and changes in intramuscular osmotic pressures force
water from the vascular compartment to the interstitial space. During
prolonged exercise, plasma volume can decrease by 10-20% and by 15-
20% in 1-minute bouts of exhaustive exercise (10). Resistance training
with 40% and 70% one repetition maximum can cause a 7.7% and 13.9%
reduction in blood plasma respectively (11).
A reduction in plasma increases the concentration of hemoglobin.
Although no extra red blood cells have been produced, the greater
concentration of hemoglobin per unit of blood significantly increases the
bloods oxygen carrying capacity. This is one of the main adaptations
during immediate acclimatization to altitude.
Blood pH can change from a slightly alkaline 7.4 at rest to as low as 6.5
during all-out sprinting activity. This is primarily due to an increased
reliance on anaerobic energy systems and the accumulation or hydrogen
ions (1).
Effect of exercise and training on respiratory system.
What is an increase in oxygen diffusion rate?
Oxygen diffusion is where the oxygen moves from the capillaries to the
tissues and carbon dioxide moves from the cells to the blood. Oxygen
diffusion rate increases after long term exercise and as a result
the oxygen and carbon dioxide will start to diffuse much quicker.
How does exercise affect the heart rate?
Like all muscles, the heart becomes stronger as a result of exercise, so it
can pump more blood through the body with every beat and continue
working at maximum level, if needed, with less strain. The resting heart rate
of those who exercise is also slower, because less effort is needed to pump
blood.
Exercise or any physical activity has a special effect on respiratory system .
We need oxygen at rest and during exercise , since energy supply to the
active muscles increases demand of oxygen . Another important function of
respiration is to eliminate carbon dioxide from the body. During exercise
cellular oxidation increases and thereby carbon dioxide production increases.
Respiratory system maintains an efficient balance between the oxygen and
carbon dioxide in the blood at rest and also during exercise. There are some
immediate changes that occur during exercise programme. Also, there are
some relatively permanent changes following long-term physical training ,
the magnitude of changes being dependent on type , intensity and duration of
exercise.
Immediate changes during exercise :
Tidal Volume : The amount of air which we inhale or exhale during
quiet breathing is called tidal volume. It is around 500 ml. During exercise ,
this tidal volume increases. Depending on intensity it may be 1500-2000 ml
for ordinary person and for well trained athlete it may be increased to 2500
ml.
Respiratory rate : Number of times one takes inspiration or expiration
in each minute is called Respiratory rate. At rest , respiratory rate is around
16 per minute. During exercise , for ordinary persons it may be increased to
25-30 per minute and for well trained athlete it may be around 38-40 per
minute.
Pulmonary Ventilation : The amount of air which passes through lungs
is each minute is called Pulmonary ventilation . The Pulmonary ventilation
(PV) = Tidal volume (TV) X Respiratory rate (RR) and therefore at rest it is
around 8 lit / min . During exercise since both TV and RR increases , PV
will also increase depending on the intensity of exercise . For ordinary
person , the value of PV may be 40-50 lit / min and for well trained athlete ,
it may be around 100 lit / min .
Oxygen uptake : The amount of oxygen which we take inside the body
from ambient air in each minute at rest is called resting oxygen uptake. It is
around 200-300 ml / min . During exercise oxygen uptake increases to 3.5 lit
/ min for ordinary person and 4.5 lit/min for well trained athlete.
Lung diffusion capacity: Diffusion is the process of movement of gas
molecules (O2 and CO2 ) that takes place in the lungs and tissues. During
exercise there will be more movement of gas molecules and diffusion
capacity increases.
Lung volume: For normal breathing at rest lung expand and there is a
change in air pressure. During exercise due to rapid movement of diaphragm
and inter costal muscles total area of lung expands to accommodate more
exchange of gases.
Long-term effect of training on Respiratory system
Tidal Volume (TV) : Trained athlete‘s capacity to inhale or exhale air
during exercise increases to the tune of 2500 ml. Untrained persons cannot
increase up to this level because their capacity is less than trained athletes.
Respiratory rate (RR): Trained athlete may increase their rate to 40 in
each minute from 16 / min at rest. Untrained persons will not be able to
reach to this level. They may increase their rate up to 25-28 / min.
Pulmonary ventilation (PV): A trained athlete may increase PV to
around 100 lit/min. This is because their TV and RR both increases during
exercise. Untrained persons may increase it up to 50-60 lit/min.
Oxygen uptake: During exercise, after long term training, a trained
athlete may consume around 5 liter oxygen per minute. Untrained persons
may go up to the level of 3.5 lit oxygen per minute.
Lung diffusion capacity: During exercise, the lung diffusion capacity
increases in both trained and untrained persons. However, trained athletes
may increase their diffusion capacity 30% more than that of an untrained
person because athlete‘s lung surface area and red blood cell count is higher
than that of the non-athletes.
Vital capacity: It is the maximum volume of air forcefully expired after a
maximal inspiration. For a healthy adult male it is around 4.8 lit and for
women 3.1 lit. The athletes who are under training for a long period may
increase vital capacity to around 6 lit.
Efficiency of lung: An athlete‘s total efficiency of the lung remains at
higher level than the non-athletes. This efficiency is the key factor for higher
rate of oxygen uptake than non-athletes.
Second wind: This term is usually described as a sudden transition from
an ill-defined feeling of distress or fatigue during the early portions of
prolonged exercise to a more comfortable, less stressful feeling later in
exercise. It has been observed that trained athletes get their second wind
comfortably and easily than non-athletes.
The respiratory system comprises of the nose, mouth, throat, larynx, trachea,
bronchi and lungs. The function of the respiratory system is to facilitate
gaseous exchange to take place in the lungs and tissue cells of the body.
Oxygen is required by cells in the body to allow various metabolic reactions
to take place and to produce energy and is therefore essential to life.
The respiratory system may be defined as the organs and tissues through
which air is passed into and out of the body to allow the necessary gaseous
exchanges to take place.
External respiration is the means by which oxygen from the air passes into
the blood stream for transportation to the tissue cells and carbon dioxide is
collected and transferred back to the lungs and expelled from the body.
Internal respiration involves the vital chemical activities that take place in
every living cell requiring oxygen and glycogen to combine and release
energy, water and carbon dioxide.
Organs of the respiratory system
The normal rate of inspiration and expiration, the respiration rate, is about
16 times a minute in an adult. Breathing is controlled
in the brain stem, which automatically regulate the rate and depth of
breathing depending on the level of carbon dioxide in the blood.
A-VO2 diff
Arterio-venous oxygen difference (A-VO2 diff) is the difference between
oxygen concentration in the arteries and the oxygen concentration in the
veins.
Hemoglobin and Myoglobin
Hemoglobin is a protein in red blood cells which enables the cells to carry
oxygen and myoglobin is an oxygen-binding protein found in heart and
skeletal muscles.
Effect of exercise on the respiratory system
In the Cardiovascular system, the benefits of exercise were discussed in
relation to the improved functioning of the heart and the lowering of blood
pressure. Combined with increased maximum oxygen consumption
(VO2 max), or lung capacity, these are all vital contributors to being fit and
healthy.
An athlete who has not properly trained their cardiovascular system is likely
to incur other injuries more easily by the rapid onset of fatigue and the
consequent lowering of motivation and mental awareness. For anyone
competing at varying altitudes, they must allow themselves a considerable
period to acclimatize before an event. Even climbing to a
moderate altitude decreases the maximum uptake by 7% to 8% due to the
change in atmospheric pressure. This decrease in oxygen being supplied to
the muscles may decrease performance by 4 to 8% depending on the
duration of competition, a considerable disadvantage at the finish line. Even
the athlete who prepares and acclimatizes well may still not match natives of
high altitude areas such as the Andes, who have a larger chest capacity, more
alveoli, larger capillary beds and higher red blood cell count. Since people
may suffer from altitude sickness when moving from low to high altitudes,
sufficient time must also be allowed for these symptoms to disappear before
starting intensive training.
Effect of exercise and training on muscular system
All muscles in the body, including those of the skeletal system and cardiac
muscle, may benefit from regular exercise. Various involuntary systems and
processes combine their effort to bring oxygenated blood to the working
muscles. The result may be improved strength, a slimmer body and better
overall health.
There are three types of muscles, including skeletal, cardiac and smooth.
Both skeletal muscles, which assist in locomotion and posture and cardiac,
found in the heart, benefit from regular activity. Hypertrophy is an increase
in skeletal muscle size, one of the most obvious effects of exercise on the
muscular system, especially from resistance or strength training. Smooth
muscle such as in the stomach and intestines is controlled
nervous system and isn‘t affected.
The body‘s muscular, cardiopulmonary, and nervous systems all respond to
increased demand of the muscles for oxygenated blood. This gets diverted
from non-vital organs to increase energy within the muscles. Byproducts
from the increased activity such as lactic acid, hydrogen ions and carbon
dioxide stimulate the respiratory system to increase breathing for better
oxygen exchange.
Effects of exercise on the muscular system show up in cardiac muscle too. A
strong heart can pump more blood each time it beats, carrying nutrients and
oxygen to all parts of the body. The pulse rate of a person who exercises
regularly will be slower than most people, because the heart doesn‘t need to
pump as much to move the same amount of blood. Steady aerobic exercise
using the major muscle groups, enough to cause an obvious increase
in respiration, is best for continued cardiac health.
Two interesting effects of exercise on the muscular system are the decrease
of inhibitory neural feedback and synchronous activation. The first process
means the nervous system lets the muscle work longer and harder than it
would if the muscle were untrained, where it might be injured. Synchronous
activation allows more muscle fibers to work in tandem, giving the muscle
an enhanced ability to handle the increased activity and perform at a higher
level. The result is a measurable strength gain, particularly in women‘s
muscles and those of adolescents. In addition, strength training with weights
and resistance bands can reverse muscular decline that comes with aging.
Warming up and cooling down can be vitally important to a proper workout.
These may prevent adverse effects of exercise on the muscular system like
strain injuries resulting from a lack of good preparation. The muscles need
adequate blood and oxygen flow to begin vigorous activity. Stretching after
the workout keeps them from tightening up and also keeps them flexible
long after the workout is finished.
Weight-bearing exercises also contribute to bone density, a primary concern
especially for women, who are more prone to osteoporosis. Tension on
muscles improves strength and balance, which when combined with higher
bone density makes fall injuries less likely. Strong, conditioned muscles at
rest burn more calories than weak muscles. Regular exercise also helps
prevent obesity, a major cause of health problems at any age.
Hypertrophy – the muscle increases in size and bulk. Hypertrophy is a result
of an increase in the volume of contractile proteins (Actin & Myosin) within
the muscle cell so they can contract with greater force. The number of
muscle fibers stays the same. In general males have a greater potential for
increases in muscle bulk due to higher levels of the hormone testosterone.
Increases in tendon strength – tendons are tough bands of fibrous connective
tissue designed to withstand tension forces along their length. Like muscles,
tendons adapt to the mechanical loading of regular exercise. A general
adaptation is increased strength but different types of training will exert
differing effects on muscle – tendon complexes. Ligaments and tendons
will increase in flexibility and strength with exercise. Articular cartilage also
becomes thicker.
Muscle stores & Mitochondria – Muscles increase their oxidative capacity
(their ability to use oxygen to produce energy) with regular training. This is
achieved by an increase in the number of mitochondria (an
organelle where aerobic energy is produced) within the muscle cells which
will increase the supply of ATP and an increase in the quantity of enzymes
involved in the production of ATP. The ability of the muscle to store
myoglobin is increased (myoglobin is like hemoglobin and carries oxygen).
Lactic acid anaerobic training stimulates the muscles to become better able
to tolerate lactic acid and clear it away more efficiently. With endurance
training the capillary network extends allowing greater volumes of blood to
supply the muscles with oxygen and nutrients. The muscles are able to use
more fate as a fuel source and become more efficient at using oxygen.
Exercise has both short and long term effects to muscular system.
Exercise works as a stimulus and gives stress to muscles.
After exercise you may feel short term effects like:
 Blood flow because of increased volume of blood that is pumped to
muscle tissue.

 Muscle fatigue is short-term decline in the ability of a muscle to generate force. Another way to describe muscle fatigue is as the shortterm inability to continue to repeat muscular contractions with the same force.

 Muscle exhaustion when exercise continues through muscle fatigue
without rest after time it can lead to muscle exhaustion.
 Muscle damage often happens, because of over-stretching without a
proper warming-up or no warming-up before intense exercise.
 Cramp uncontrollable and very painful muscle contraction.
After some time passes then long term effects on muscles takes place
like:
 Muscle size increases mainly due to muscle ability to adapt to stress
over a period of time which increases them in size.
 Muscle coordination increases when doing exercises which require
skill and technique e.g.: dribbling ball.
 Blood supply to muscles increases due to long-term exercise by that
improving delivery of various nutrients, minerals and vitamins to
muscles and making them more effective and faster at regenerating
after injury or workout.
Short term effects such as:
 Blood flow – after exercise you can notice that muscle tissue (warm
muscle) is bigger than cold muscle, because of blood flow into them. It
can increase by up to 25 times, because muscle requires more energy
and oxygen.
 Muscle fatigue – is the decline in ability of a muscle to generate force.
It can be a result of intense exercise, but abnormal fatigue may be
caused by barriers to or interference with the different stages of muscle
contraction. There are two main causes of muscle fatigue. The
limitations of a nerve‘s ability to generate a sustained signal (neural
fatigue) and the reduced ability of the muscle fiber to contract
(metabolic fatigue).
 Muscle exhaustion – general exhaustion often occurs after you have
done too much activity at one time, such as by taking an extra-long
hike. You may feel weak and tired, or your muscles may be sore. These
sensations usually go away within a few days. In rare cases,
generalized muscle weakness may be caused
problem, such as problems with body regulating the distribution of
energy to muscles and organs.
 Muscle damage – any effort beyond muscle ability level or accident
can tear the fibers and cause muscle damage. When muscle fibers are
damaged, the body immediately starts to repair it at the cellular level.
Muscles most of the time repairs by themselves (if body is functioning
properly) through time. If damage or injury is critical, surgery might be
needed.
 Cramp – because of over-exercise, lack of nutrients like magnesium or
bad blood circulation when muscles don‘t receive enough oxygen. It is
very painful and can be dangerous if doing exercise that involves heavy
weights alone.
Long-term effects of exercise
 Muscle size – is mostly determined by persons genetics, but can be
affected with life choices like: anabolic steroids, exercise, and healthy
food. Exercising specific muscles regularly can increase their size by
up to 60%. This increase in muscle size is mainly due to increased
diameter of individual muscle fibres.
 Muscle coordination – It trains muscles to work more efficient and
effectively by working together. E.g.: when the prime mover contracts
more rapidly the antagonist (muscle) must also relax as quickly to
prevent blocking the movement.
 Blood supply – As a result of frequent exercise over a sustained period
of time both the quantity of blood vessels and the extent of the
capillary beds increases.
Effects of exercise on muscular system would benefit by increasing size and
number of mitochondria, improved perception of muscle tone and also
overall improved:
 Coordination
 Power
 Balance
 Speed
 Agility
 Body composition
 Reaction time
 Muscular endurance
 Flexibility
Physiological concept of physical fitness,
Warming up, Conditioning and fatigue.
Introduction
The formal dance class has long been considered the cornerstone of training,
providing all the technical, physical and aesthetic requirements of dance. In
recent years a considerable amount of research has been carried out
regarding the health of dancers. Findings from this research indicate that
many dancers are not as fit and healthy as they could be. It has also been
found that there is a discrepancy in the physical intensity level between
training, rehearsal, and performance. This means that training methods,
which are generally based on tradition, are not sufficient to help prepare
dancers for the higher, more physically demanding aspects of performance.
In light of these studies, and with increased understanding of the artistic and
athletic needs of dancers in different genres, it is no longer acceptable to
train dancers without preparing them physiologically for the demands of
current choreographic work.
What is Fitness, and why is it Beneficial?
For dancers, the whole body (physical and psychological) is their
instrument, their means of artistic expression. Dance calls upon all aspects of
fitness. Good fitness is key to reducing the risk of injury, enhancing
performance, and ensuring longer dancing careers. A healthy dancer is one
who is in a state of being ‗well‘ in both body and mind. A physically fit
dancer is one who has the ability to meet the demands of a specific physical
task at an optimal level. The goal of improving dancers‘ fitness is to
minimize the difference between the dancer‘s individual maximal abilities
and their performance requirements, so that they can become the best dancer
possible.
What Types of Fitness Are Most Important for a Dancer and Why?
While research indicates that some dance styles require certain elements of
fitness more explicitly than others, in a well-rounded dance training
program, it is necessary to consider all the components of fitness.
The components of fitness are:
Aerobic fitness – associated with moderate, longer-term levels of activity.
Anaerobic fitness – associated with high intensity, maximal, short bursts of
activity.
Muscle endurance – the ability of a muscle to produce continuous
movement.
Strength – the ability of a muscle to produce a maximal force on one
occasion.
Power – the explosive (speed-related) aspect of strength.
Flexibility – the range of motion at a joint in association with the pliability
of a muscle.
Neuromuscular coordination – associated with balance, agility,
coordination and skill.
Body composition – the make-up of body weight by percentage of muscle
and fat.
Rest – a period of no activity, to allow for recovery and regeneration.
While any change in traditional dance training regimens must be approached
cautiously to ensure that enhanced artistry and expression remain the
primary goals, it may be suggested that unless dancers are physiologically
honed to the same extent as they are artistically, their physical conditioning
may potentially be the limiting factor in their development. Ignoring the
physiological training of today‘s dancers could eventually hamper the
development of the art form. It is the continual responsibility of dance
teachers and educators to develop their knowledge and understanding of the
physiological demands of dance, and be aware of the options for either
integrating physical fitness training into the technique class itself or
providing it through supplementation.
In a recent study, full time contemporary dance students completed a year of
weekly dance fitness classes alongside their regular technique training.
Students perceived positive physiological adaptations such as reductions in
fatigue, improvement in general energy levels and an improved capacity in
their dance classes to sustain technique and jumping ability. The importance
of warm up and cool down was also commonly cited and the recognition of
the relationship between fitness and injury prevention was highlighted.
More than twenty years ago it was stated that the best dancers have an
integrated combination of two talents: knowledge of what is to be expressed
and the physical and mental tools to accomplish that expression. A dancer
who is able to jump higher, balance longer and create illusions such as
floating may not necessarily be a better dancer, but she does have the
advantage of a greater range of tools with which to produce the desired
images of dance choreography. Although a topic of continual debate, more
recent research has since indicated that a fitter dancer is a better dancer.

Which Activities Improve Various Types of Fitness?

Aerobic Training

The greater a dancer‘s aerobic capacity, the longer they can work at
moderate heart rates before becoming fatigued. Research suggests that dance
will only elicit an improvement in aerobic capacity in a very unfit group of
people, or if an aerobic dance class is taken. The average dance technique
class is too intermittent in nature for any positive aerobic effect to occur. In
order to improve aerobic capacity, the body needs to work hard enough to
bring about change or adaptation within the body. Specifically, a rise in
heart rate to approximately 70 – 90% of maximum (HRmax) will stress the
aerobic energy system. This elevation in heart rate has to be maintained
between 20 and 40 minutes, three times a week. Continuous movement
activities, such as running, aerobics classes, swimming, cycling, and
skipping, are good examples of aerobic exercise.
Although there are variations among teachers, a primary intention of the
technique class is dance skill acquisition. Developing high levels of
technical skill and movement economy requires a different focus from
developing the aerobic capacity of the dancer. However, technique classes
can be modified to involve some degree of aerobic work, using simple
repetitive movements. Simple movement repetition helps to stress the
aerobic energy system rather than stress skill acquisition. Warm up could be
conducted in a continuous manner at a higher intensity than normal, and
center or traveling sequences could be longer, with less rest time, allowing
an aerobic foundation to develop. Familiar movement combinations might
be performed over consecutive classes, purely for the benefit of continuous

repetition rather than artistic effect.

Anaerobic Training

Anaerobic training utilizes activity that is of a maximal, ‗all-out‘ effort for
short periods of time. An exercise-to-rest ratio of 1:3 is recommended for
training the threshold at which lactate starts to accumulate in the blood
stream, thus hindering muscle function. An exercise-to-rest ratio of 1:5 is
recommended for training the source of the fastest muscle actions: high
energy phosphates, adenosine triphosphate (ATP) and creatine phosphate
(CP). Optimum exercise time for each bout can gradually increase from 10 –
50 seconds. The intensity of activity for the whole duration should be near
maximal heart rate (95 – 100% HRmax). Rest periods should be at a low
intensity exercise, as this promotes faster recovery. Examples of anaerobic

exercises include sprints, quick steps, jumps, and fast skipping.

Strength/Endurance Training

The role of strength training in dance has frequently been misunderstood.
There are still concerns in the dance world that increased muscle strength
will negatively affect flexibility and aesthetic appearance. However,
research has demonstrated that supplemental strength training can lead to
better dancing and reduced occurrences of dance injuries, without interfering
with key artistic and aesthetic requirements.
For an optimal strength training program, it has been suggested that
exercises be specific to the desired outcome. Strength training can involve
very heavy weights/resistance with minimal repetitions for a relatively short
amount of time, or exercises can involve light weights/resistance with many
repetitions for a prolonged time. Each program targets a specific goal. A
combination of high intensities (70 – 100% of maximum) and low volumes
of work, two to three times a week, aims to increase muscle strength. A full
recovery period (5 – 6 minutes) is essential between sets in this instance.
Dancers wanting to increase muscle endurance are prescribed a combination
of moderate intensities (60 – 70% maximum) and high volumes of work,
three to four times a week. The rest periods are then shorter (2 – 4 minutes)

so that the next set of exercises begins before full recovery.

Power Training

Jumping is an integral part of most dance performances and involves the use
of both muscular strength and elasticity. Studies report that polymeric
(jump) training has been shown to have a positive effect in dancers.
However, there are warnings that polymeric training must be approached
gradually and systematically to avoid injury. A good starting point is to
design exercises in which dancers are encouraged to jump in a neutral
position without emphasizing artistic skill, but instead simply focusing on
jumping higher. Once the dancers have gained greater understanding of how
to elevate themselves, they can bring correct dance technique back into the

movements while trying to maintain as much height as possible.

Flexibility Training

Flexibility is an important element of physical fitness. It is crucial in
complimenting muscular strength, building efficiency in movement,
coordination, and preventing injuries. Holding muscles in a stretched
position for a prolonged amount of time causes the muscle fibers to become
accustomed to the new length, therefore increasing flexibility. For it to be
beneficial, the specific muscle group being stretched needs to be isolated.
For example, when stretching the hamstrings, spinal movement should be
reduced. Relaxation is also important. It is advised that stretches happen
slowly and gently with coordinated inhalation and exhalation at the moment
of maximum stretch (i.e., refrain from holding the breath).
There are many different types of stretching including static (holding),
dynamic (moving through the stretch), and proprioceptive neuromuscular
facilitation (PNF; a method utilizing alternate contraction and relaxation). It
is important to be aware of the advantages and disadvantages of each. For
example, ballistic (bouncing) stretches are not considered useful and can
lead to muscle soreness and injury. Contrary to the practice of many dancers,
stretching to full range should be carried out when the body is warm,

preferably after class.

Neuromuscular Coordination

Moving beyond the purely physiological parameters, dance fitness also
involves balance, agility, coordination and skill. Out of all the components
of fitness, it is likely that neuromuscular coordination is addressed most
often in the actual dance technique class. Through the use of imagery and
visualization, improved neural pathways can help facilitate and develop
efficiency in movement. Neuromuscular coordination can positively affect
levels of muscle strength by controlling the recruitment of the right number
of muscle fibers at the right time. In others words, dancers can become more
skillful in recruiting only the muscles required to produce a certain
movement and thus sustain sufficient energy levels and reduce fatigue.
Research into motor control and motor learning also offers invaluable
information that can enhance neural re-patterning, coordination and muscle

relaxation.

Body Composition

Body composition plays an important role in dancers‘ health. Appropriate
and healthy ratios of lean muscle mass to fat mass are key factors that can
contribute to optimizing physical performance. Body composition is often
expressed as a percentage of body fat and healthy recommendations suggest
that dancers‘ body fat be at a certain level in order reach their potential.
According to the World Health Organization, healthy body compositions
range from 17 to 25% for females and below 15% for males (but not too low
as a certain amount of fat is essential for daily healthy function). Optimal
body composition is going to vary from activity to activity. These
measurements are useful to determine what the best make-up is for dancers
so that they can jump higher, turn faster, and physically survive long days of
training, rehearsing, and performing. A balance of appropriate energy intake
(nutrition) and energy expenditure (physical activity) will help dancers
achieve the body composition that is right for them.
Rest
The importance of rest in dance training cannot be stressed enough. Proper
recovery from physical training has many benefits. Rest helps to accelerate
muscle regeneration between training sessions, to decrease fatigue, and to
decrease the incidence of injury. It has been appreciated relatively recently
that continuous training beyond a certain threshold of physical activity,
without sufficient rest, can negatively impact both the health and
performance of dancers. This concept refers to overtraining – excessive
training that results in no effect or even negative effects on a dancer‘s
performance. When there is an imbalance between habitual exertion
(training) and recovery, symptoms such as severe and prolonged fatigue,
changes in behavior and a loss of motivation can result. Recommendations
to prevent or reverse overtraining include monitoring dance quality versus

quantity, diet, hydration, rest, and sleep patterns.

General Training Principles

The following variables of exercise training also need to be understood in
constructing balanced training plans. Depending on the dancer‘s
training/performance goal, it is often necessary to progress to a higher level
of difficulty by increasing the intensity, volume and/or frequency of training
over time. Otherwise, the body simply adapts to the training and fitness
levels plateau. Also fundamental to training is the concept of overload,
which means that the body must be challenged above a certain threshold to
provide sufficient stimulus for improvement to occur. Normally encountered
stress will maintain but not increase the level of conditioning. For example,
if the demands of a dance class are too similar from day to day there will be
insufficient overload for desired improvement to take place. Sport literature
describes another principle called specificity, and recommends that to
develop motor abilities; training exercises should use similar technical
patterns and kinematic structure to the particular activity for which it is
preparing the athlete/dancer.
What is Physical Fitness?
Physical fitness is an important concept as related to the fields of physiology
and exercise physiology. You should take a few minutes and read this brief
history of Fitness. You'll note that this fitness idea is not something that just
recently burst onto the scene.
There are a number of definitions for physical fitness but I developed the
following general definition many years ago:
Physical fitness is the relative state of optimal function. All humans are able to
be active because of the physiology / function of multiple body systems. Each
of us has an optimal function which is unique to us and based largely on genetic
endowment. We can improve that function by systematically engaging in
various activities. The term relative is comparative in nature and so we may
be more or less fit than we were or more or less fit than others with similar
genetic endowment.
Other definitions of physical fitness include the following:
If you are physically fit, you are free from illness, and able to function
efficiently and effectively, to enjoy leisure, and to cope with
emergencies. Health-related components of physical fitness include body
composition, cardiovascular fitness, flexibility, muscular endurance, and
muscle strength. Skill-related components include agility, balance,
coordination, power, reaction time, and speed.
Physical fitness comprises two related concepts: general fitness (a state
of health and well-being) and specific fitness (a task-oriented definition
based on the ability to perform specific aspects of sports or occupations).
Physical fitness is generally achieved through exercise, correct nutrition
and enough rest. It is an important part of life.
The state or condition of being fit; suitability or appropriateness. Good
health or physical condition, especially as the result of exercise and
proper nutrition.
When considering physical fitness we usually consider it as having two
components, health related fitness and skill related fitness.
As a physical education professional you will be responsible for knowing these
concepts and later, for being able to describe how would one would exercise
or train in such a way as to improve any of these components.
Types of physical fitness

Physical fitness is a general concept and is defined in many ways by different scientists. Physical fitness is discussed here in two major categories: healthrelated physical fitness and motor-performance physical fitness. Despite some overlap between these classifications, there are major differences, as described below.

Health-related physical fitness
Health-related physical fitness is defined as fitness related to some aspect of
health. This type of physical fitness is primarily influenced by an individual‘s
exercise habits; thus, it is a dynamic state and may change. Physical
characteristics that constitute health-related physical fitness include strength
and endurance of skeletal muscles, joint flexibility, body composition, and
cardio respiratory endurance. All these attributes change in response to
appropriate physical conditioning programs, and all are related to health.
Strength and endurance of skeletal muscles of the trunk help maintain correct
posture and prevent such problems as low back pain. Minimal levels of
muscular strength and endurance are needed for routine tasks of living, such as
carrying bags of groceries or picking up a young child. Individuals with very
low levels of muscular strength and endurance are limited in the performance
of routine tasks and have to lead a restricted life. Such limitations are perhaps
only indirectly related to health, but individuals who cannot pick up and hug a
grandchild or must struggle to get up from a soft chair surely have a lower
quality of life than that enjoyed by their fitter peers.
Flexibility, or range of motion around the joints, also ranks as an important
component of health-related fitness. Lack of flexibility in the lower back and
posterior thigh is thought to contribute to low back pain. Extreme lack of
flexibility also has a deleterious effect on the quality of life by limiting
performance.
Body composition refers to the ratio between fat and lean tissue in the body.
Excess body fat is clearly related to several health problems,
including cardiovascular disease, type II (adult-onset) diabetes mellitus, and
certain forms of cancer. Body composition is affected by diet, but exercise
habits play a crucial role in preventing obesity and maintaining acceptable
levels of body fat.
Cardio respiratory endurance, or aerobic fitness, is probably what most people
identify as physical fitness. Aerobic fitness refers to the integrated functional
capacity of the heart, lungs, vascular system, and skeletal muscles to expend
energy. The basic activity that underlies this type of fitness is aerobic
metabolism in the muscle cell, a process in which oxygen is combined with a
fuel source (fats or carbohydrates) to release energy and produce carbon
dioxide and water. The energy is used by the muscle to contract, thereby
exerting force that can be used for movement. For the aerobic reaction to take
place, the cardio respiratory system (i.e., the circulatory and pulmonary
systems) must constantly supply oxygen and fuel to the muscle cell and remove
carbon dioxide from it. The maximal rate at which aerobic metabolism can
occur is thus determined by the functional capacity of the cardio respiratory
system and is measured in the laboratory as maximal oxygen intake. As will be
discussed in detail below, aerobic fitness is inversely related to the incidence
of coronary heart disease and hypertension.
Motor-performance physical fitness
Motor-performance fitness is defined as the ability of the neuromuscular
system to perform specific tasks. Test items used to assess motor-performance
fitness include chin-ups, sit-ups, the 50-yard dash, the standing long jump, and
the shuttle run (a timed run in which the participant dashes back and forth
between two points). The primary physical characteristics measured by these
tests are the strength and endurance of the skeletal muscles and the speed or
power of the legs. These traits are important for success in many types
of athletics. Muscular strength and endurance are also related to some aspects

of health, as stated above.

There is disagreement among experts about the relative importance of healthrelated and motor-performance physical fitness. While both types of fitness are obviously desirable, their relative values should be determined by an individual‘s personal fitness objectives. If success in athletic events is of primary importance, motor-performance fitness should be emphasized. If concern about health is paramount, health-related fitness should be the focus.

Different types of fitness may be important not only to different individuals but
also to the same individual at different times. The 16-year-old competing on a
school athletic team is likely to focus on motor performance. The typical
middle-aged individual is not as likely to be concerned about athletic success,
emphasizing instead health and appearance. One further point should be made:
to a great extent, motor-performance physical fitness is determined by genetic
potential. The person who can run fast at 10 years of age will be fast at age 17;
although training may enhance racing performance, it will not appreciably
change the individual‘s genetically determined running speed. On the other
hand, characteristics of health-related physical fitness, while also partly
determined by inheritance, are much more profoundly influenced by exercise
habits.
Principles of exercise training
Research in exercise training has led to the recognition of a number of general
principles of conditioning. These principles must be applied to the development
of a successful exercise program.
Specificity
The principle of specificity derives from the observation that the adaptation of
the body or change in physical fitness is specific to the type of training
undertaken. Quite simply this means that if a fitness objective is to increase
flexibility, then flexibility training must be used. If one desires to develop
strength, resistance or strengthening exercises must be employed. This principle
is indeed simple; however, it is frequently ignored. Many fraudulent claims for
an exercise product or system promise overall physical fitness from one simple
training technique. A person should be suspicious of such claims and should
consider whether or not the exercise training recommended is the type that will
produce the specific changes desired.
Overload
Overload, the second important principle, means that to improve any aspect of
physical fitness the individual must continually increase the demands placed on
the appropriate body systems. For example, to develop strength, progressively
heavier objects must be lifted. Overload in running programs is achieved by
running longer distances or by increasing the speed.
Progression
Individuals frequently make the mistake of attempting too rapid a fitness
change. A classic example is that of the middle-aged man or woman who has
done no exercise for 20 years and suddenly begins a vigorous training program.
The result of such activity is frequently an injury or, at the least, stiffness and
soreness. There are no hard-and-fast rules on how rapidly one should progress
to a higher level of activity. The individual‘s subjective impression of whether
or not the body seems to be able to tolerate increased training serves as a good
guide. In general it might be reasonable not to progress to higher levels of
activity more often than every one or two weeks.
Warm-up/cool down
Another important practice to follow in an exercise program is to gradually
start the exercise session and gradually taper off at the end. The warm-up
allows various body systems to adjust to increased metabolic demands. The
heart rate increases, blood flow increases, and muscle temperatures rise.
Warming up is certainly a more comfortable way to begin an exercise session
and is probably safer. Progressively more vigorous exercises or a gradual
increase in walking speed are good ways to warm up. It is equally important
to cool down—that is, to gradually reduce exercise intensity—at the end of
each session. The abrupt cessation of vigorous exercise may cause blood to
pool in the legs, which can cause fainting or, more seriously, can sometimes
precipitate cardiac complications. Slow walking and stretching for five minutes
at the end of an exercise session is therefore a good practice. The heart rate
should gradually decline during the cool down, and by the end of the five
minutes it should be less than 120 beats per minute for individuals under 50
years of age and less than 100 beats per minute for those over 50.
Frequency, intensity, and duration
To provide guidance on how much exercise an individual should do, exercise
physiologists have developed equations based on research. It is generally
agreed that to develop and maintain physical fitness, the exercise must be
performed on a regular basis. A frequency of about every other day or three
days per week appears minimally sufficient. Many individuals exercise more
frequently than this, and, of course, such additional exercise is acceptable
provided that one does not become over trained and suffer illness or injury.
The intensity of exercise required to produce benefits has been the subject of
much study. Many people have the impression that exercise is not doing any
good unless it hurts. This is simply not true. Regular exercise at 45 to 50
percent of one‘s maximal capacity is adequate to improve one‘s physiological
functioning and overall health. This level of intensity is generally comfortable
for most individuals. A reliable way to gauge exercise intensity is to measure
the heart rate during exercise. An exercise heart rate that is 65 percent of a
person‘s maximal heart rate corresponds to approximately 50 percent of his
maximal capacity. Maximal heart rate can be estimated by subtracting one‘s
age in years from 220 (or, in the case of active males, by subtracting half of
one‘s age from 205). Thus, a sedentary 40-year-old man has an estimated
maximal heart rate of 180 beats per minute. Sixty-five percent of this maximal
rate is 117 beats per minute; thus by exercising at 117 beats per minute, this
individual is working at about 50 percent of his maximal capacity. To
determine exercising heart rate, a person should exercise for several minutes, to
allow the heart rate to adjust. The exerciser should then stop exercising, quickly
find the pulse, and count the number of beats for 15 seconds. Multiplying this
by four gives the rate in beats per minute. The pulse must be taken immediately
after stopping exercise, since the heart rate rapidly begins to return to the
resting level after work has been stopped. As noted above, exercising at the 50
percent level of intensity will improve physiologic functioning and provide
health benefits. This level of exercise will not produce the maximum fitness
needed for competitive athletics.
Overall conditioning
Much emphasis has been given in the foregoing discussion to aerobic fitness,
because this form of conditioning is extremely important. It should be noted,
however, that other types of conditioning also have benefits. A total exercise
program should include strengthening exercises, to maintain body mass and
appropriate levels of strength for daily functioning, and stretching exercises to
maintain joint mobility and flexibility. The specificity principle described
above indicates that no one exercise is likely to produce the overall
conditioning effect. In general an exercise plan should consist of aerobics,
exercises that increase the strength and endurance of various skeletal muscle
groups, and flexibility exercises to maintain good joint function.
Individual differences
The principles of exercise training discussed above should be viewed as general
guidelines. Individuals differ in both physiological and psychological
adaptations to exercise. Two people who are similar in many respects and who
start the same exercise program may have entirely different impressions of it.
One person may feel that the exercise is too easy, while the other may believe
that it is much too hard. It is certainly appropriate that the exercise plan be
adjusted to account for preferences. Likewise some individuals will progress to
more intense training levels far more rapidly than others do. As mentioned
earlier, exercise progress should be adjusted according to the exerciser‘s own
assessment.
Individuals also differ in the type of exercise they like or can tolerate. Jogging,
for instance, is not for everyone. Many people who dislike jogging, or who
suffer running injuries, can find other satisfactory exercise activities, such as
cycling, walking, swimming, or participating in a sport. Many kinds of exercise
activities are appropriate and can provide physiological and health benefits to
the participant. There is no one best exercise. The important thing is to be
regular in exercise participation and to follow the general guidelines outlined in
this section.
Physiological effects of exercise

Neuromuscular effects