Exerciseand Heat StrokeJoseph M. Warpeha, MA, CSCS, *D, NSCA-CPT, *D

S ummer is right around the cor-

ner which makes this a good

time to talk about the prob-

lems that can be brought on by exercise

or physical exertion in hot environ-

ments. The human body is remarkable

in its ability to adapt to environmental

extremes as highlighted by indigenous

peoples living in climates that rangefrom Alaska and Siberia to the tropicsof Central America and the deserts of

Africa. The body does have its limits

however, particularly for those who havenot been born and raised in an extreme

environment or, at the very least, have

not acclimatized (adapted).

Heat stroke (HS) is a medical emergencyand is the most severe of all heat illness

Table 1. RiskFactors for Heat Stroke

es. HS is a failure of the hypothalamic

temperature regulatory center due to a

rising core temperature. In other words,

the thermostat that keeps our body

temperature in a fairly narrow operating

range "breaks down" and results in anuncontrolled rise in core temperature

that can quickly become fatal if appro-

priate measures are not taken. Death canbe due to a multitude of complications

arising from the HS cascade includingheart failure or cerebral edema (3). The

mortality associated with HS has been

quoted between 10 - 50% (4).

HS is classified as either classical or

exertional with only minor differences

between the two. The diagnostic criteriafor classical heat stroke are: 1) central

nervous system dysfunction (e.g. confu-

sion, unconsciousness), 2) hot dry skin,

and 3) core temperature >410C (:t1°C

depending on the source) (3). Core tem-

perature should be measured rectally forthe most accurate assessment (2). The

only difference in criteria for exertional

HS is that the core temperature may

be slightly lower and profuse sweating

is often present (although skin may

be wet or dry at the time of collapse).

Other symptoms of HS include rapid

heartbeat, rapid and shallow breathing,

altered blood pressure (elevated or low-

ered), altered mental statUs, vomiting,diarrhea, seizures, and coma. Classical

HS often occurs during extreme heat

waves with the elderly and very young

being particularly vulnerable. Exertional

HS typically occurs in previously healthy

young people who perform heavy orintense exercise in hot and/or humid

environments. The classic example is a

football player participating in two-a-

day practices in a helmet and full pads

during a Midwest summer heat wave.

A temperate climate like the Midwest

is a good example because there can beextreme heat waves with drastic swings

Major Risk Factors for Heat StrokeEnvironment,

- High t~lJIperature- High humidity- Hf9b sofar radiation- Little or rio'wind .

Physical. Actiyity

- VigoroJts eXe~~ise

- Heavy exertion- Intenseaetiv'ities

Age- Older than 75

.-Younger tnah"S

NSCA's Performance Training Journal I www.nsca-lift.org/perform Vol.5 No.2 I Page6

Other Risk Factors For Heat Stroke

Male gender Lack of acdimatization Lack of fitness

previous heat stroke WearJng eq::ssi¥eclothing Qbesity '" ","''''"" ,,'

Dehydration Fatigue Illness/Disease

Malnutrition Akohol use'"

Certain Medkations 0"

in temperature and many people arenot acclimatized to the heat like those

who live in hot climates and are more

adapted to the heat and humidity. Thecombination of an intense physical sport

like football and heavy equipment that

deters heat dissipation is particularly

dangerous in hot environments. All ath-

letes (not just football players) who

spend time training/competing in a hotenvironment must take precaUtions to

prevent heat illnesses.

HS is the most frequent environmen-

tally-related cause of death in the U.S.

with about 400 deaths per year attrib-

uted to it (6). Surprisingly, HS is second

only to head injuries in exercise-related

deaths (3) and is the third leading cause

of death among athletes in the U.S.

(6), so the consequences of this heatillness should not be underestimated.

HS affects virtually all of the body's vital

systems including cardiovascular, neuro-

logical, renal, gastrointestinal, immuno-

logical, and musculoskeletal (4).

The major risk factors for HS include a

hot environment, vigorous exercise/exer-

tion, and age. Risk factors for HS arelisted in Table 1.

\

\

Since a hot environment is the major

ingredient, it is important to take intoaccount all of the factors that contribute

to this heat (high environmental tem-

perature and solar radiation) as well asthose that make it more difficult for the

body to dissipate heat (high humidityand little or no wind). The wet-bulb

globe temperature (WGBT) is a singleindex that accounts for these factors

(except wind) in an attempt to quantify

heat stress and pr~vent heat illness (5).

A more familiar method of determininghow hot it "feels" is the heat index which

factors the combination of temperature

and humidity (see Figure 1). Althoughthe heat index does not include the

effects of wind or radiant heat, it is a

good quantification of heat stress on thebody and is usually more readily avail-

able to the general public via the newsmedia (television, radio, and newspa-

pers).The cornerstone to treating HS is low-

ering the core temperature as rapidly

as possible (7). Chances of survival are

greatly improved if core temperaturecan be lowered to under 38.9OC within

30 minUtes (4). Rapid cooling can be

achieved in numerous ways including:immersion in cold water or ice bath,

promoting evaporative heat loss (using

a fan), and the use of body cooling

suits. Other components of the acute

management stage (particularly in the

absence of medical personnel/facilities)

are calling 911, placing the person in

the supine position with feet elevated,

vigorous hydration, and maintenance of

an open airway. Excess clothing should

be removed and ice packs applied to the

neck, groin, and axillae (armpit) (3).

If the person is still oUtside, he or sheshould be moved into the shade.

The best defense against heat stroke and

other heat illnesses is prevention and

precaution. The most important precau-

tion is to pay attention to heat warnings

issued by the National Weather Service

and limit or avoid exercise in danger-

ously hot conditions. Limiting direct

sun exposure is important because the

radiant heat can add up to 150F tothe heat index (6). If exercise in the

heat is unavoidable, maintaining ade-

quate hydration levels and salt/electro-

lyte stores during prolonged exertion is

paramount. For the athlete or exerciser,

acclimatizing oneself to hot conditionsover several days or weeks is the most

effective way to gradually introduce the

body to a hot environment. This causes

adaptive mechanisms to take place and

allows the thermoregulatory system to

function more efficiently in hot envi-

ronments. If you must train in the heat,

acclimatizing yourself and following the

above precautions is the best prevention

of serious heat illness including heatstroke.

References1.American Collegeof Sports Medicine.(2006). ACSMs guidelines for exercisetesting and prescription, 7th edition.Baltimore: Lippincott Williams &Wilkins.

2. Asrrand PO, Rodahl K, Dahl HA,Str0mme SB. (2003). Textbookof workphysiology: physiological bases of exer-cise, 4th edition. Champaign: HumanKinetics.

3. Brooks GA, FaheyTD, Baldwin KM.(2005) Exercisephysiology:human bioen-ergeticsand its applications,4th edition.New York:McGraw-Hill.

4. Grogan H, Hopkins PM. (2002).Heat stroke: implications for criticalcare and anaesthesia. British Journal ofAnaesthesia,88:700 - 707.

5. McArdle WD, Katch FI, Katch VL.

(1996). Exercisephysiology:energy,nutri-tion, and human performance, 4th edi-tion. Baltimore:Williams & Wilkins.

6. Moreau Tp, Deeter M. (2005). Heatstroke-predictable, preventable, treat-able. Journal-American Academy ofPhysician Assistants, 18(8):30 - 35.

NSCA's Performance Training Journal I www.nsca-lift.org/perform Vol. 5 No.2 I Page7

7. Rhoades RA, Tanner GA. (2003).

Medical physiology, 2nd edition.Baltimore: Lippincott Williams &Wilkins.

About the AuthorJoe Warpeha is an exercise physiologist

and strength coach and is currently work-

ing on his PhD in exercisephysiology at

the University of Minnesota-Minneapolis.

His current researchfocuses on bone and

tendon adaptations to training and the

effects of skeletal loading on their physi-

olfJgical and mechanical properties. Joe

teaches several courses at UM including

"advanced weight training and condition-

ing" and "measurement, evaluation, and

research in kinesiowgy': He has a masters

degree in exercisephysiowgy and certifica-

tions through the NSCA, ACSM, USAiV,

ASEp, and YMC4. He has over 14 years of

resistance and aerobic training experience

and has been a competitive powerlifter

since 1997. Joe is a two-time national

bench press champion and holds multiplestate and national records in the bench

press while competing in the 148, 165,

and 181-pound weight classes.

Figure 1. Calculation of heat index and associated risks of heat illness.Reprinted with permission from the Oklahoma Climatology SurveyOklahoma Climatology Survey. (2006). Heat Index Chart. Retrieved 2/21/06, from http://okfirst.ocs.ou.edu/train/materials/Heat/humid.gif

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73

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