Accuracy and Reliability of Core Temperature Measurement Tools
in Identifying Heat-Related Illnesses in Athletes
California University of Pennsylvania
recognition of injuries and illnesses is a responsibility of the Certified
Athletic Trainer. Heat-related
illnesses (HRIs) can be more effectively prevented when they are recognized at
an early stage. Core temperature is
one indicator of HRI, but the accuracy of measurement tools is questionable. Certified Athletic Trainers can recognize these conditions more
efficiently in athletes by analyzing the accuracy and reliability of current and
developing core temperature measurement tools in conjunction with other
indicators of HRI.
Illnesses (HRIs) are plotted along a continuum that leads from mild to severe
early recognition by a Certified Athletic Trainer, a mild or moderate HRI can be
prevented from progressing to a severe and possibly life threatening condition. Signs and symptoms along with core temperature should be
assessed to determine the presence of HRIs. Core temperature is the only objective measure that a Certified Athletic
Trainer can use to detect a HRI. Mild
HRIs are not related to an increased core temperature and should be diagnosed
symptomatically, as recommended by the National Athletic Trainers’ Association
(NATA) position statement on exertional heat illnesses.1 The mild
HRIs are heat edema and heat rash; although they are uncomfortable, they are not
life-threatening. The HRIs are
considered to be moderate are heat syncope and heat cramps. Heat syncope does not result from an increased core temperature, but heat
cramps are the body’s earliest indicator of such an elevation.1, 2 Early recognition at this phase is a key factor in effective prevention
of progression along the continuum to a severe HRI. Severe HRIs are heat exhaustion and heat stroke. These life-threatening conditions can be recognized by an increased core
temperature. The core temperature
during heat exhaustion is between 37°C and 40°C (98.6°F-104°F).2 Heat stroke is recognized by an increased core temperature over 40°C
(104°F) and can be categorized based on the circumstances causing the illness.1,
2 Classic heat stroke is
based on environmental factors alone that cause an increased core temperature;
exertional heat stroke is caused by exercise which causes the body’s core
temperature to increase in any environmental condition.2 Tachycardia, altered mental status, emesis, hyperventilation, and seizure
are some of the most severe and apparent signs and symptoms of heat stroke.1 If the athlete continues without treatment, heat stroke can ultimately
lead to coma and death.1 Any
core temperature over 40°C (104°F) is considered a medical emergency and
should be treated by cooling the athlete immediately followed by hospitalization
with constant monitoring of vitals.1,2 When Certified Athletic Trainers are comfortable monitoring core
temperature with accurate and reliable devices, earlier recognition and
prevention can occur more often, possibly resulting in fewer athletes suffering
The Gold Standard and
the New Generation
gold standard of core temperature measurement is currently rectal thermometry,
which measures the temperature 8-10 cm inside the rectum. Rectal thermometry is recommended by both the NATA and the American
College of Sports Medicine (ACSM) for recognition of HRIs.1, 3 The rectal thermometer has been shown in studies to be the most accurate
and reliable thermometer during exercise and is used in most studies as the
control variable to test other types of thermometers.4-6 Rectal temperatures can be measured by using a flexible thermometer that
is inserted 8-10 cm into the rectum and secured by applying medical tape to the
wire lead. The measurement site is
considered to be accurate and easily accessible before, during, and after
exercise. The reading device is
easy to carry or attach to clothing during exercise; it can be left in place
during exercise since the thermometer itself is inserted into the rectum, to
allow immediate core temperature measurement at any time during exercise.
other type of thermometer has been shown to be accurate and reliable during
exercise in current research is the ingestible telemetric pill, measures
intestinal temperature.4, 7-10 Telemetry is the automated recording
of specified measurements that are transmitted electronically. The ingestible telemetric pill measures core temperature by recording
temperature measurements and then transmits that reading to a receiver via
radio, infrared, or ultrasonic signal.11 In studies by Casa (2007) and Ganio (2009), ingestible telemetry was
tested against rectal thermometry and other common thermometers. These studies reported significant positive correlations between
ingestible telemetry and rectal thermometry and proclaimed the pill to be both
accurate and reliable.4, 7 The
theory behind ingestible telemetry and intestinal temperature is that
measurements closer to the core will be more accurate. Although this type of thermometer has been examined in many studies, more
research is necessary before it should be included in recommendations by the
NATA and ACSM.
Reliability of Current Tools
temperature measurement during exercise is an effective way to objectively
recognize HRIs but only if the measurement devices are accurate and reliable. They should also be practical and functional in all environments. Rectal thermometers are the gold standard because they are accurate and
reliable in all conditions, as illustrated in two classic studies by Casa (2007)
and Ganio (2009). These studies had
similar protocols and tested the same thermometer types: oral, axillary, aural,
gastrointestinal, forehead, temporal, and rectal. The most notable difference between studies was setting, one
was performed outdoors and the other indoors. Both studies showed that of all the thermometers tested, only the rectal
and ingestible telemetric pill were accurate and reliable.4, 7 These findings indicate that the environment has little effect on these
types of thermometers and further demonstrates their reliability and validity.
factors affect the accuracy and reliability of these instruments. The location of a rectal thermometer can be uncomfortable 5
and insertion, as it is an invasive measure, can be viewed as inappropriate
touching if not handled with professionalism.6 The lag phenomenon is also a problem, but it does not cause concern of
enough significance to make the rectal thermometer inaccurate.4, 7 The lag phenomenon is thought to be caused by poor blood supply to the
rectum, the presence of feces at the time of measurement, and postural
differences during the recovery period.12 There are also speculations about the practical use of ingestible
telemetric pills because of their detailed time schedule and possible diet
challenges. The pills should be
taken 3-4 hours prior to activity and with a prescribed diet,7 which
naturally suggests that this method should be used for prevention and not an
emergency situation. Not all types
of telemetric pills are disposable with retrieval after exercise difficult,
opening a doorway for contamination upon the next use. More research is necessary to fully determine future recommendations for
the use of ingestible telemetry pills during exercise.
are several other common types of thermometers that are used for athletics
today. Although most of them are
considered to be accurate and reliable in the clinical setting, during exercise
their use is questionable. These
thermometers include esophageal, aural tympanic, oral, and temporal artery
thermometers. Current research
proclaims that these tools are not recommended for use during exercise by
Certified Athletic Trainers.4, 7, 9, 10, 13 Research showed that esophageal thermometers are accurate and reliable
during exercise, but the location of thermometer, at heart level inside the
esophagus, can be uncomfortable for the athlete and easily influenced by any
substance entering the esophagus.4, 7, 9, 10 Aural tympanic thermometers are easy to use and popular for their
non-invasive location,6 but they are not accurate or reliable during
exercise.4, 7 Neither oral nor temporal artery thermometers are considered
accurate or reliable either. These
two types of thermometers have been used by sports medicine professionals for
years, but current research shows that too many external factors affect these
instruments to create an accurate or reliable measurement.4, 7, 13 Each for their separate reasons, these thermometers are not recommended
for use by Certified Athletic Trainers on athletes during exercise.
The recommendations by the NATA and
ACSM are for the use of rectal thermometry to recognize HRIs in athletes during
exercise. This should not be used
in isolation of the signs and symptoms, which also lead to early recognition and
treatment for prevention. Although
mild HRIs are not related to an increased core temperature, moderate and severe
HRIs will present with an increased core temperature. Current research shows that intestinal temperatures, as
assessed by an ingestible telemetric pill, are as accurate and reliable as
rectal temperatures, but there is not enough research on this device to include
it in recommendations for Certified Athletic Trainers.
Binkley HM, Becket J, Casa DJ, Kleiner DM, Plummer PE. National Athletic Trainers’ Association position
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- Howe AS, Boden BP. Heat-related
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- Armstrong LE, Casa DJ, Millard-Stafford M, Moran DS, Pyne SW, Roberts WO. American College of Sports Medicine
position stand: exertional heat illness during training and competition. Med Sci Sports Exerc.2007;39(3):556-572.
- Ganio MS, Brown CM, Casa DJ, et al. Validity and reliability of devices that assess body temperature during
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- Moran DS, Mendal L. Core temperature measurement methods and current insights. Sports Med. 2002;32(14):879-885.
- Newsham KR, Saunders JE, Nordin ES. Comparison of rectal and tympanic thermometry during exercise. South
Med J. 2002;95(8):804-810.
- Casa DJ, Becker SM, Ganio MS, et al. Validity of devices that assess body temperature during outdoor exercise
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- Engels H, Yarandi H, Davis J. Utility of an ingestible capsule for core temperature measurements during body
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- Gant N, Atkinson G, Williams C. The validity and reliability of intestinal temperature during intermittent
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- O'Brien C, Hoyt RW, Buller MJ, Castellani JW, Young AJ. Telemetry pill measurement of core temperature in
humans during active heating and cooling. Med Sci Sports Exerc. 1998;30(3):468-472.
- Güler NF, Ubeyli ED. Theory and applications of biotelemetry. J Med Syst. 2002;26(2):159-178.
- Edwards RJ, Belyavin AJ, Harrison MH. Core temperature measurement in man. Aviati Space Environ Med. 1978;49(11):1289-1294.
- Ronneberg K, Roberts WO, McBean AD, Center BA. Temporal artery temperature measurements do not detect hyperthermic
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