INTRODUCTION
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.
1. 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.
2. 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.
3. 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 (nonoxygen) 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, psychologic, 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
hyperpnea.
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 runs 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 pulmonary-respiratory 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 a 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,
cardiorespiratory 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 dioxide-absorbing canisters.
The Circulatory System
Blood
transports oxygen, energy subtrates, 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 by relative
circulatory 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 lose 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.
1. 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.
2. 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.
3. 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.
4. 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 undescended
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 glenohumeral
dislocations, acromioclavicular 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.
Nondisabling congenital defects are judged relative to the
risk involved. For example, nonsymptomatic spondylolisthesis
without spina 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 bronchiospasm during exercise.
Nonasthmatic 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 a profuse or
commonly bloody sputum demands a full investigation.
Cardiovascular Considerations
The largest percentage of nontraumatic 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,
tachycardias, 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 pseudonephritis,
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.
Hemoglobinuria
In the
healthy, hemoglobinuria may be noted after prolonged walking or
running. It is often associated with boxing, karate, wrestling,
hard trauma, and players who assume a forced crouching position
(eg, football linemen, baseball catchers). In the latter group,
minor renal dysfunction and nephroptosis are often related.
Hemoglobinuria and hematuria are rarely seen in female
athletes.
Traumatic Nephroptosis
Dolan and
Holladay report that right nephroptosis has shown in about 22% in
boxers as compared to 1%-2% in nonboxers. This high incidence is
attributed to frequent, strenuous, long-duration crouching and
trauma to the supporting bands. The kidneys are subjected to both
macrotrauma and microtrauma in many sports. Repeated minor
macrotrauma results in permanent renal scars (athlete's kidney),
observed late as a pericalyceal and peripelvic deformity.
Strenuous exercise, stress, forced crouching, or external blows
or forces may produce renal microtrauma, evidenced by painless
hematuria. Major kidney trauma is characterized by flank pain,
tachycardia, profuse hemorrhage, gastrointestinal symptoms,
rigidity of abdominal muscles, fever, and sometimes shock.
Alimentary Considerations
Constipation and abdominal pains are often presenting complaints. Constipation
is frequently the result of preoccupation with body activity, and
ignorance in the wide range of normal bowel movements. It is
commonly due to simple dehydration from inadequate fluid intake.
Gastrointestinal "stitches" commonly result from eating shortly
before vigorous exercise or a functional abdominal weakness. Well
controlled diabetes is not a reason for exclusion by itself, but
short-duration sports are preferred to avoid the risks of
hypoglycemia.
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