National Athletic Trainers Association Position Statement: Exertional Heat Illnesses

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National Athletic Trainers Association
Position Statement Exertional Heat Illnesses
Helen M. Binkley Joseph Beckett Douglas J.
Casa Douglas M. Kleiner Paul E.
Plummer?Mesa State College, Grand Junction,
CO University of Charleston, Charleston, WV
University of Connecticut, Storrs, CT
University of Florida, Jacksonville, FL
?Indiana State University, Terre Haute, IN
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Definitions

• Exercise-Associated Muscle (Heat) Cramps
• Heat Syncope
• Exercise (Heat) Exhaustion
• Exertional Heat Stroke
• Exertional Hyponatremia

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Recommendations
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3. Acclimation
Adapt athletes to exercise in the heat
(acclimatization) gradually over 10 to 14 days.
Progressively increase the intensity and duration
of work in the heat with a combination of
strenuous interval training and continuous
exercise. Well-acclimatized athletes should
train for 1 to 2 hours under the same heat
conditions that will be present for their event.
In a cooler environment, an athlete can wear
additional clothing during training to induce or
maintain heat acclimatization. Athletes should
maintain proper hydration during the
heat-acclimatization process.
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Acclimatization

• One hour of exercise for 5 days in greater than
  30C
• Some people require 5-10 days with 2-4 hours of
  exercise per day
• Intense exercise is more effective than
  over-distance training however, reduce intensity
  by 60-70 at the first
• Exposure to hot dry climates provides only
  partial acclimatization

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Acclimatization
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Acclimatization - Cardiovascular

• 3-27 increase in plasma volume
• Maintains blood volume, stroke volume, and
  sweating capacity
• Lower heart rate at the same exercise intensty
• Body can hold more heat
• Increases in PV due to hormonal changes (ADH and
  renin) and increase in plasma proteins
• Decrease in skin blood flow

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Acclimatization Sweating Response

• Increase in sweating capacity from 1.5 to 4.0
  liters
• More even distribution of sweat
• Less NaCl in sweat
• Increase sensitivity of sweat glands
• Lower sweating threshold
• Better transfer of heat loss, less blood flow to
  skin

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Acclimatization Metabolic

• Less anaerobic, more aerobic
• Less reliance on glycogen as a fuel by 50-60
  prolong exercise time

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Acclimatization

• Significant changes in PV, HR and RPE occur in
  first 3-6 days
• Changes in sweat concentration take about 10 days
• Changes in sweat rate take 14 days
• Acclimation to the heat improve performance in
  cool temperatures
• Changes are not permanent fit people remain
  acclimated longer than less fit people

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Table 4. Physiologic Responses After Heat
Acclimatization Relative to Nonacclimatized State
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Table 4. (continued)
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5. Fluid Intake
5. Educate athletes to match fluid intake with
sweat and urine losses to maintain adequate
hydration. (See the National Athletic Trainers'
Association Position Statement Fluid Replacement
in Athletes.) Instruct athletes to drink
sodium-containing fluids to keep their urine
clear to light yellow to improve hydration and to
replace fluids between practices on the same day
and on successive days to maintain less than 2
body-weight change. These strategies will lessen
the risk of acute and chronic dehydration and
decrease the risk of heat-related events.
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6. Sleep Diet
Encourage athletes to sleep at least 6 to 8 hours
at night in a cool environment, eat a
well-balanced diet that follows the Food Guide
Pyramid and United States Dietary Guidelines, and
maintain proper hydration status. Athletes
exercising in hot conditions (especially during
twice-a-day practices) require extra sodium from
the diet or rehydration beverages or both.
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Valtin H "Drink at least eight glasses of water
a day." Really? Is there scientific evidence for
"8 x 8"?SourceAm J Physiol Regul Integr Comp
Physiol 2002 Nov 283(5) R993-1004 Despite the
seemingly ubiquitous admonition to "drink at
least eight 8-oz glasses of water a day" (with an
accompanying reminder that beverages containing
caffeine and alcohol do not count), rigorous
proof for this counsel appears to be lacking.
This review sought to find the origin of this
advice (called "8 x 8" for short) and to examine
the scientific evidence, if any, that might
support it. The search included not only
electronic modes but also a cursory examination
of the older literature that is not covered in
electronic databases and, most importantly and
fruitfully, extensive consultation with several
nutritionists who specialize in the field of
thirst and drinking fluids. No scientific studies
were found in support of 8 x 8. Rather, surveys
of food and fluid intake on thousands of adults
of both genders, analyses of which have been
published in peer-reviewed journals, strongly
suggest that such large amounts are not needed
because the surveyed persons were presumably
healthy and certainly not overtly ill. This
conclusion is supported by published studies
showing that caffeinated drinks (and, to a lesser
extent, mild alcoholic beverages like beer in
moderation) may indeed be counted toward the
daily total, as well as by the large body of
published experiments that attest to the
precision and effectiveness of the osmoregulatory
system for maintaining water balance. It is to be
emphasized that the conclusion is limited to
healthy adults in a temperate climate leading a
largely sedentary existence, precisely the
population and conditions that the "at least" in
8 x 8 refers to. Equally to be emphasized, lest
the message of this review be misconstrued, is
the fact (based on published evidence) that large
intakes of fluid, equal to and greater than 8 x
8, are advisable for the treatment or prevention
of some diseases and certainly are called for
under special circumstances, such as vigorous
work and exercise, especially in hot climates.
Since it is difficult or impossible to prove a
negative-in this instance, the absence of
scientific literature supporting the 8 x 8
recommendation-the author invites communications
from readers who are aware of pertinent
publications.
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Sports Science Exchange 92VOLUME 17 (2004)
Number 1DIETARY WATER AND SODIUM REQUIREMENTS
FOR ACTIVE ADULTS W. Larry Kenney, Ph.D., FACSM
Meeting Daily Water Needs The challenge of
accurately and clearly identifying
population-wide guidelines for nutrient intake is
evident in this statement from the DRI report
"on a day to day basis, fluid intake, driven by
thirst and the consumption of beverages at meals,
allows maintenance of hydration status and total
body water at normal levels" (Institute of
Medicine, 2004, p. S-5). This seemingly simple
statement is at once correct, incorrect, and
somewhat misleading. The correct part of the
statement is that, on a daily basis, most healthy
adults do consume enough water from drinking a
variety of beverages (providing about 80 of
daily water needs) and eating food (providing the
remaining 20) to maintain health and proper
physiological function. The incorrect portion
of the statement is that thirst determines how
much we drink day in and day out. Actually, it is
largely behavior and not thirst that dictates
daily fluid intake (Phillips et al., 1984). We
drink when we eat, we drink when we pass a water
fountain or the kitchen refrigerator, and we
drink when cold, palatable fluids are readily
available, such as at social gatherings, parties,
or meetings. Thirst has very little to do with
this sort of daily fluid-in, fluid-out
calculation at all. We become thirsty when our
bodies sense either a decrease in body water
(sensed as a low blood volume) or, more often, an
increase in sodium concentration (primarily
sensed by cells of the brain). Therefore, we
experience the sensation of thirst only when our
bodies are stressed by fairly significant fluid
losses or changes in sodium status (both of which
can be altered by fluid deprivation, prolonged
sweating, diuresis, diarrhea, and vomiting). Even
when we do experience thirst, the sensation is
not well correlated with the body's fluid needs
(Hubbard et al., 1984). Both the American College
of Sports Medicine (ACSM) and the National
Athletic Trainers' Association (NATA) issued
press releases soon after the IOM report,
cautioning physically active people against
"letting their thirst guide them." Rather, the
clear and important health message should be that
thirst alone is not the best indicator of
dehydration or the body's need for fluid, a fact
that is particularly true during exercise.
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SODIUM THE FORGOTTEN NUTRIENTSSE 78 VOLUME 13
(2000), NUMBER 3 Michael F. Bergeron, Ph.D.,
FACSM
Optimal concentrations of sodium in body fluids
are critical for many bodily functions, including
transmission of nerve impulses and contraction of
the heart and skeletal muscles. A loss of just a
few grams of sodium can disturb the concentration
of sodium around specific nerve endings and
muscle fibers and lead to muscle cramps, and a
loss of 14 grams can lead to serious illness. In
some individuals, each liter of sweat can contain
1.8 grams of sodium or more, and sweating can
occur at rates as high as 2 liters/hour or
greater, making large losses of water and sodium
possible. A failure to replace sodium can lead to
incomplete rehydration and may predispose the
athlete to heat cramps during exercise. Moreover,
excessive drinking of plain water, soft drinks,
or other very low-sodium fluids are relatively
ineffective for rapid rehydration and, in certain
individuals, can result in hyponatremia (low
blood sodium), which can be deadly. Thus, any
time considerable sweating occurs or is
anticipated, appropriate fluid intake with an
accompanying increase in dietary sodium can help
prevent problems related to a sweat-induced
sodium deficit and incomplete or inappropriate
rehydration.
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7. WBGT
Develop event and practice guidelines for hot,
humid weather that anticipate potential problems
encountered based on the wet-bulb globe
temperature (WBGT) (Table 3) or heat and humidity
as measured by a sling psychrometer (Figure 1),
the number of participants, the nature of the
activity, and other predisposing risk factors.
If the WBGT is greater than 28C (82F, or very
high as indicated in Table 3, Figure 1), an
athletic event should be the nature of the
activity, and other predisposing risk factors. If
the WBGT is greater than 28C (82F, or very
high as indicated in Table 3, Figure 1), an
athletic event should be delayed, rescheduled, or
moved into an air-conditioned space, if
possible. It is important to note that these
measures are based on the risk of environmental
stress for athletes wearing shorts and a T-shirt
if an athlete is wearing additional clothing (ie,
football uniform, wetsuit, helmet), a lower WBGT
value could result in comparable risk of
environmental heat stress (Figure 2).
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7. WBGT
If the event or practice is conducted in hot,
humid conditions, then use extreme caution in
monitoring the athletes and be proactive in
taking preventive steps. In addition, be sure
that emergency supplies and equipment are easily
accessible and in good working order. The most
important factors are to limit intensity and
duration of activity, limit the amount of
clothing and equipment worn, increase the number
and length of rest breaks, and encourage proper
hydration. Modify activity under high-risk
conditions to prevent exertional heat illnesses.
Identify individuals who are susceptible to heat
illnesses. In some athletes, the prodromal signs
and symptoms of heat illnesses are not evident
before collapse, but in many cases, adept medical
supervision will allow early intervention.
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The Wet Bulb Globe Temperature (WBGT)

• The WBGT was developed in the late 1950s for the
  US Marine Corps Recruit Depot on Parris Island in
  South Carolina. Humidity in this region can be
  quite high and Marines have to undergo vigorous
  training exercise in military clothing, under
  full sun. There is a significant risk of heat
  injury if precautions are not taken.
• The WBGT was later used by researchers as an
  easily measured general heat-stress index. In
  time its use widened. Because its use is
  recommended in the Standard, ISO 7243, it is
  often used in Occupational Health and Safety
  guidelines for working in hot environments. It
  has been advocated for use in sports requiring
  continuous exertion, such as the marathon. It is
  also used for horses in equestrian events.

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The Wet Bulb Globe Temperature (WBGT)

• The WBGT is measured by a simple
  three-temperature element device .
• The first temperature, (Tg), is measured by the
  black globe thermometer. The black globe
  temperature represents the integrated effects of
  radiation and wind.
• The second thermometer measures the natural
  wet-bulb temperature (Tnwb). It consists of a
  thermometer with its bulb covered with a wettened
  cotton wick supplied with distilled water from a
  reservoir. Evaporation from the wettened bulb
  cools the thermometer. This thermometer
  represents the integrated effect of humidity,
  wind and radiation.
• The final temperature element is the (shade) air
  temperature (Ta). It is measured by a thermometer
  shielded from radiation - generally by being
  placed in a weather screen.
• The three elements Tg, Tnwb, and Ta are combined
  by into a weighted average to produce the WBGT.
• WBGT (0.7 Tnwb) (0.2 Tg) (0.1 Ta)

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Table 3. Wet-Bulb Globe Temperature Risk Chart
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Figure 1. Risk of heat exhaustion or heat stroke
while racing in hot environments
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Figure 2. Heat stress risk temperature and
humidity graph
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8. Check the environmental conditions before and
during the activity, and adjust the practice
schedule accordingly. Schedule training sessions
to avoid the hottest part of the day (10 AM to 5
PM) and to avoid radiant heating from direct
sunlight, especially in the acclimatization
during the first few days of practice sessions.
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9. Plan rest breaks to match the environmental
conditions and the intensity of the activity.
Exercise intensity and environmental conditions
should be the major determinants in deciding the
length and frequency of rest breaks. If possible,
cancel or postpone the activity or move it
indoors (if air conditioned) if the conditions
are extreme or hazardous (see Table 3) or very
high (see Figure 1) or to the right of the
circled line (see Figure 2). General guidelines
during intense exercise would include a workrest
ratio of 11, 21, 31, and 41 for extreme or
hazardous (see Table 3) or very high (see
Figure 1), high, moderate, or low
environmental risk, respectively. For activities
such as football in which equipment must be
considered, please refer to Figure 2 for
equipment modifications and appropriate workrest
ratios for various environmental conditions. Rest
breaks should occur in the shade if possible, and
hydration during rest breaks should be encouraged.
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10. Implement rest periods at mealtime by
allowing 2 to 3 hours for food, fluids,
nutrients, and electrolytes (sodium and
potassium) to move into the small intestine and
bloodstream before the next practice.
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11. Provide an adequate supply of proper fluids
(water or sports drinks) to maintain hydration
and institute a hydration protocol that allows
the maintenance of hydration status. Fluids
should be readily available and served in
containers that allow adequate volumes to be
ingested with ease and with minimal interruption
of exercise. The goal should be to lose no more
than 2 to 3 of body weight during the practice
session (due to sweat and urine losses). (See the
National Athletic Trainers' Association Position
Statement Fluid Replacement in Athletes.)
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12. Weigh high-risk athletes (in high-risk
conditions, weigh all athletes) before and after
practice to estimate the amount of body water
lost during practice and to ensure a return to
pre-practice weight before the next practice.
Following exercise, athletes should consume
approximately 11.25 L (34-50 oz) of fluid for
each kilogram of body water lost during exercise.
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13. Minimize the amount of equipment and clothing
worn by the athlete in hot or humid (or both)
conditions. For example, a full football uniform
prevents sweat evaporation from more than 60 of
the body. Consult Figure 2 for possible equipment
and clothing recommendations. When athletes
exercise in the heat, they should wear
loose-fitting, absorbent, and light-colored
clothing mesh clothing and new-generation cloth
blends have been specially designed to allow more
effective cooling.
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Clothing

• Dry clothing retards heat exchange more than
  soaking wet clothing
• Cottons and linens readily absorb moisture
• Loose fitting clothing
• Light colored clothing
• Cool max, Hydroweave, etc.

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Clothing

• Seal off up to 50 of the bodys surface from the
  benefits of evaporative cooling
• Extra weight of 6-7 kilograms adds additional
  heat stress

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14. Minimize warm-up time when feasible, and
conduct warm-up sessions in the shade when
possible to minimize the radiant heat load in
high or very high or extreme or hazardous
(see Table 3, Figure 1) conditions.
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15. Allow athletes to practice in shaded areas
and use electric or cooling fans to circulate air
whenever feasible.
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18. Mandate a check of hydration status at
weigh-in to ensure athletes in sports requiring
weight classes (eg, wrestling, judo, rowing) are
not dehydrated. Any procedures used to induce
dramatic dehydration (eg, diuretics, rubber
suits, exercising in a sauna) are strictly
prohibited. Dehydrated athletes exercising at the
same intensity as euhydrated athletes are at
increased risk for thermoregulatory strain (see
the National Athletic Trainers' Association
Position Statement Fluid Replacement in
Athletes).
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Children

• Lower sweat rate
• Higher skin and core temperature
• Lower cardiac output
• Lower exercise economy
• Longer to acclimate
• Higher Na in sweat

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Older Individuals
Concern for those with existing heart disease 1
bpm higher per 1º C above 23.9º C (75º
F) Decreased ability to maintain PV early
dehydration
Delayed onset of sweating Decrease
vasodilation However, aging shouldnt increase
the risk for heat illness like it does
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Women

• Greater number of sweat glands
• Lower sweat rate
• Similar tolerance to heat compared to men when
  body fat and fitness level are the same