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
Relative humidity (percent)
rol~I~I~I~I~I.I~I~I~I~I~lro140
135
130
125
Ii:' 120a....!
!I.~ 105 It4I-~ 100 bgl,.~;1§
95 187 c90 919394 '62 ~8
85 78 8t
87 881'~O'"
82838485
~;. "'q;-8487 88 89
90183 84 85 86
7' 80
79'1ao 81 81 828385
74 14 75 75 76 76 77 77 18 78 79
77 77 78 79'8073 74 75 76
75 69 6' 10 7t 12 72 73Q:CMt1itc2000. Okl8l'Olla ClmttOlO!:lfcat SIrieY.
73
NSCA's Performance Training Journal I www.nsca-lift.org/perform Vol. 5 No.2 I Page8