physical activity in hot , humid environments is common over a wide range of sports and conditioning settings .
some athletes may also purposefully train in hot , humid environments for the adaptations related to training acclimation and environmental acclimatization ( 23 ) . in such , athletes , coaches , and sports medicine professionals alike
tracking core body temperature ( tc ) during exercise in hot and humid conditions can help mitigate the risk of heat illness ( 2 ) .
traditionally , tc has been measured in environmental researchers by invasive probing of the esophagus ( 4 , 9 , 10 , 27 ) , nasal opening ( 8 , 13 , 26 ) , or rectum ( 4 , 10 , 13 , 20 , 27 ) .
however , the aforementioned tc measures are not readily available to the public and are impractical during exercise outside of a laboratory setting .
non - invasive temperature monitoring using relatively inexpensive temporal , tympanic , and oral measurement devices are adequate surrogates for tc at rest and during light activity in thermoneutral settings ( 14 , 21 ) .
however , their usefulness as a tc monitoring tool during higher intensity exercise in a hot , humid environment is of question ( 10 , 13 , 23 ) .
recent development of a small , single - use , ingestible tc thermistor for field use allows athletes and practitioners to circumnavigate logistical limitations associated with traditional invasive laboratory - based tc monitors .
the ingested device transmits real time temperature information from the alimentary canal to an external monitor and has been validated independently ( 6 , 22 ) .
however , the efficacy of measuring tc using superficial , non - invasive monitoring techniques relative to an internalized device has not been assessed during exercise in a hot and humid setting .
the purpose of the present study was to evaluate four such alternate , non - invasive measurements of tc ( temporal , two tympanic devices , and oral ) compared to an ingestible thermistor during exercise in a hot , humid environment . by cross - validating using bland - altman analysis with these commonly available methods ,
we hope to gain insight regarding their potential to monitor heat illness risk in a sports conditioning setting .
this study was conducted in accordance with the guidelines outlined by the declaration of helsinki . prior to any formal testing
, this experiment was reviewed and approved by the university of north texas ( unt ) institutional review board .
subjects gave written and verbal consent after a member of the study staff explained the risks and benefits related to participation in this study .
a total of 14 young , active adults ( 8 men and 6 women ) completed the study ( table 1 ) .
consented subjects underwent preliminary screening consisting of a medical history questionnaire and were excluded if they self - reported any contraindication to exercise ( 1 ) . after completing the questionnaire
, subjects underwent body composition analysis ( % bf ; lunar prodigy ; madison , wi ) and a standard graded exercise test previously used in our laboratory ( 4 ) .
briefly , subjects began the exercise test at 3.0 mph and speed was increased ( men : 2.0 mph ; women : 1.5 mph ) every 3 minutes until voluntary exhaustion .
heart rate ( polar t31 ; lake success , ny ) and oxygen uptake ( medgraphics ultima cpx ; st paul , mn ) were continuously monitored throughout the exercise test .
subjects reported to the laboratory one day prior to their exercise trial and were given a packaged thermometer pill ( cortemp temperature sensor ; hq , inc . ; palmetto , fl ) .
subjects were asked to orally ingest the pill approximately 12 hours before reporting to the laboratory the following morning .
city , state ) logged and digitally stored values of heart rate and tc every 20 seconds .
after exercise completion , subject data were downloaded to a pc in spreadsheet format for subsequent analysis .
telemetry pill measurement of core temperature has been established as representative of tc ( 6 , 22 ) .
the devices were : tympanic 1 ( t1 ) ( welch allyn braun pro 4000 ; skaneateles falls , ny ) ; tympanic 2 ( t2 ) ( covidien genius2 ; mansfield , ma ) ; temporal ( exergen temporal scanner ; watertown , ma ) ; and oral ( welch allyn sure temp plus 690 ; skaneateles falls , ny ) .
a member of the study staff familiar with all devices recorded the temperatures at each site .
the measurement site was medial to the hairline at the anatomical temple for consistency within and across exercise tests .
subjects reported to the laboratory after a 12-hour exercise abstention and 8-hour fast and were instructed to hydrate with water prior to arrival .
upon arrival , subjects provided a urine sample for specific gravity assessment using a handheld meter ( atago 3741 pen - urine ; tokyo , japan ) .
subjects were deemed euhydrated if urine specific gravity ( usg ) was < 1.025 ( normal range = 1.0001.030 ) . if the subject s usg was 1.025 , then they consumed 500 ml of water and waited 30 minutes before providing another urine sample .
after the subjects were confirmed to be euhydrated , they were escorted into a heated ( 35.5  0.6 c ) and humidified ( 53.9  5.8 % rh ) environmental chamber and completed 45-minutes of staged treadmill exercise .
the exercise trial was designed to cause a gradual rise in body temperature for 20 minutes , then a rapid increase through minute 45 .
this design was intended to roughly mirror what a runner might experience when warming up and competing in a hot , humid environment . as such ,
the exercise was comprised of seven stages ( 2 walking , 5 running ; figure 1 ) . during the exercise trial
, subjects were allowed to consume water ( 212 ml / kg body weight ) immediately after each temperature data collection but were asked to refrain from pouring water on them , as this may have altered temperature measurements .
this study was conducted in accordance with the guidelines outlined by the declaration of helsinki . prior to any formal testing
, this experiment was reviewed and approved by the university of north texas ( unt ) institutional review board .
subjects gave written and verbal consent after a member of the study staff explained the risks and benefits related to participation in this study .
a total of 14 young , active adults ( 8 men and 6 women ) completed the study ( table 1 ) .
consented subjects underwent preliminary screening consisting of a medical history questionnaire and were excluded if they self - reported any contraindication to exercise ( 1 ) . after completing the questionnaire
, subjects underwent body composition analysis ( % bf ; lunar prodigy ; madison , wi ) and a standard graded exercise test previously used in our laboratory ( 4 ) .
briefly , subjects began the exercise test at 3.0 mph and speed was increased ( men : 2.0 mph ; women : 1.5 mph ) every 3 minutes until voluntary exhaustion . heart rate ( polar t31 ; lake success , ny ) and oxygen uptake ( medgraphics ultima cpx ; st paul , mn ) were continuously monitored throughout the exercise test .
subjects reported to the laboratory one day prior to their exercise trial and were given a packaged thermometer pill ( cortemp temperature sensor ; hq , inc .
subjects were asked to orally ingest the pill approximately 12 hours before reporting to the laboratory the following morning .
city , state ) logged and digitally stored values of heart rate and tc every 20 seconds .
after exercise completion , subject data were downloaded to a pc in spreadsheet format for subsequent analysis .
telemetry pill measurement of core temperature has been established as representative of tc ( 6 , 22 ) .
the devices were : tympanic 1 ( t1 ) ( welch allyn braun pro 4000 ; skaneateles falls , ny ) ; tympanic 2 ( t2 ) ( covidien genius2 ; mansfield , ma ) ; temporal ( exergen temporal scanner ; watertown , ma ) ; and oral ( welch allyn sure temp plus 690 ; skaneateles falls , ny ) .
a member of the study staff familiar with all devices recorded the temperatures at each site .
the measurement site was medial to the hairline at the anatomical temple for consistency within and across exercise tests .
subjects reported to the laboratory after a 12-hour exercise abstention and 8-hour fast and were instructed to hydrate with water prior to arrival . upon arrival
, subjects provided a urine sample for specific gravity assessment using a handheld meter ( atago 3741 pen - urine ; tokyo , japan ) .
subjects were deemed euhydrated if urine specific gravity ( usg ) was < 1.025 ( normal range = 1.0001.030 ) . if the subject s usg was 1.025 , then they consumed 500 ml of water and waited 30 minutes before providing another urine sample .
after the subjects were confirmed to be euhydrated , they were escorted into a heated ( 35.5  0.6 c ) and humidified ( 53.9  5.8 % rh ) environmental chamber and completed 45-minutes of staged treadmill exercise .
the exercise trial was designed to cause a gradual rise in body temperature for 20 minutes , then a rapid increase through minute 45 .
this design was intended to roughly mirror what a runner might experience when warming up and competing in a hot , humid environment . as such
, the exercise was comprised of seven stages ( 2 walking , 5 running ; figure 1 ) . during the exercise trial ,
subjects were allowed to consume water ( 212 ml / kg body weight ) immediately after each temperature data collection but were asked to refrain from pouring water on them , as this may have altered temperature measurements .
the limits of agreement for the t1 bland - altman plot were  1.90 c ( figure 2a ) .
review of the plot revealed that : 1 ) t1 temperature tended to be lower than the pbtc , but were within the limits of agreement ; 2 ) the distribution of the differences shifted to negative above 38.0 c ; and 3 ) more ( 5.4% ) values were above the upper limit of agreement compared to the number below ( 1.8% ) the lower limit of agreement .
there was no difference in mean temperature between t1 and pbtc measurements across all time points .
results from the paired t - tests at individual time points are summarized in table 2 . across all time points , t1 and pbtc temperatures
were positively correlated ( 0.357 ; p<0.001 ) . at 0 minutes , t1 and pbtc temperatures
the limits of agreement for the t2 bland - altman plot were  2.15 c ( figure 2b ) .
the plot showed that : 1 ) t2 temperature tended to be greater than pbtc across the temperature range ; 2 ) the distribution of the differences was unchanged across the temperature range ; and 3 ) more ( 5.4% ) values were above the upper limit of agreement compared to the number below the lower limit of agreement ( 2.7% ) .
across all time points , the mean temperature for t2 was statistically greater than the mean pbtc ( 37.8  0.7 c vs. 37.6  1.0 c ; respectfully ) ( p=0.008 ) .
results from the paired t - tests at individual time points are summarized in table 2 . across all time points ,
the limits of agreement for the temporal bland - altman plot were  2.98 c ( figure 2c ) .
review of the plot showed that : 1 ) temporal measurements were generally lower than pbtc , although the difference is not apparent until temperatures reach 38.0 c ; 2 ) the distribution of the differences shifted to primarily negative above 38.0 c ; and 3 ) more ( 5.4% ) values were above the upper limit of agreement compared to the number below the lower limit of agreement ( 3.6% ) .
no statistically significant differences were observed in the means of temporal and pbtc measurements across time points .
results from the paired t - tests at individual time points are summarized in table 2 .
temporal and pbtc were positively correlated ( 0.262 ; p=0.005 ) across all time points . at 0-minutes , temporal temperature and pbtc
the limits of agreement for the oral measure bland - altman plot were  1.90 c ( figure 5 ) .
review of the plot revealed that : 1 ) oral measurements were lower than pbtc ; 2 ) the distribution of the differences shifted exclusively lower when pbtc rose above 37.6 c ; and 3 ) values were all below the upper limit of agreement compared to 7.2% below the lower limit of agreement .
( 37.0  0.4 c vs. 37.6  1.0 c , respectively ) ( p<0.001 ) .
results from the paired t - tests at individual time points are summarized in table 2 . across all time points , oral and pbtc
were positively correlated ( 0.262 ; p=0.010 ) . at 0-minutes , oral temperature and pbtc
were positively correlated ( 0.597 ; p=0.024 ) . there were no correlations at any other time point .
the purpose of the present study was to cross - validate four non - invasive tc alternates to pbtc during intermittent exercise in a hot , humid environment using the methods of bland - altman .
this study will help inform athletes , coaches , and sports medicine practitioners monitoring body temperature during physical activity in hot , humid environments .
we have shown that tympanic , specifically t1 , and temporal temperatures provided the best representation of pbtc .
( 16 ) used an earplug containing a thermocouple during exercise in 35 c , observing that this method differed from rectal temperature by > 0.5 c . however , another exercise investigation in hot , humid conditions indicated that tympanic might , in fact , correlate with tc as assessed by rectal probe ( 17 ) .
the present study was designed with normal exercise clothing in a carefully controlled ( heat and humidity ) environment .
of the two tympanic devices tested in the present study , t1 best - matched pbtc throughout the heat - stressed exercise challenge .
the t2 measure was statistically greater than mean pbtc , which could initiate premature field - based heat illness preventative care .
considering previous literature and the results of the present study , care should be taken when choosing tympanic measurement devices to estimate core body temperature when exercising in hot , humid environments .
methodological differences may account for the inconsistent findings of temporal tracking of tc during exercise in previous investigations ( 11 , 14 , 15 , 24 ) .
( 15 ) concluded that tc and temporal temperatures were statistically different during whole - body passive heat stress while wearing a 34 c water - perfused suit .
using an exercise protocol in typical clothing similar to that in the present study ( 36.4 c , 52% rh ) , ganio et al .
temporal measures failed to track rectal tc during hyperthermia in marathon runners compared to rectal tc in a study by ronnenberg and colleagues ( 25 ) . in the present study , temporal temperatures correlated with pbtc throughout the exercise session .
oral temperature has failed to match rectal or esophageal tc during exercise in the heat in numerous studies ( 7 , 12 , 18 ) .
a literature review by mazerolle and colleagues ( 19 ) concluded that oral temperature could not replicate rectal or esophageal tc measures .
this conclusion is supported by results from males and females during indoor ( 12 ) and outdoor ( 7 ) exercise in a hot and humid environment . in the present study ,
in the current protocol , tc of 37.6 c was achieved after 30 minutes of exercise . taken together ,
oral temperatures underestimate tc and should not be relied on for tracking heat illness risk during exercise .
ingestible thermistors are an established surrogate for tc ( 6 , 22 ) and were chosen for this study as esophageal and rectal tc assessments were not available for this investigation .
oral temperatures could have been affected by respiration and cooling of the mouth through convection ( 19 ) .
however , there were no measurable air currents on the exercising subjects that might have influenced the temporal and oral readings via face cooling ( 28 ) .
it is possible that water consumption was increased in subjects when exercising beyond thirty minutes compared to the first stages of exercise when average tc reached 37.6 c .
water consumption was not allowed the minute prior to each measurement time point , but it is possible that the water temperature still influenced temperature measurements .
similar results have previously been demonstrated ( 3 , 7 , 12 , 19 ) and , although this is a limitation in the present study , it still represents an obstacle experienced both on the field and on job sites when body temperature is a concern and fluid intake is not monitored .
additionally , we can not discount the possible effects of water ingestion on pbtc during our protocol . in summary ,
the key finding of the present study is that tympanic ( welch allyn braun pro 4000 model ) and temporal ( exergen temporal scanner ) devices can be used as alternate measures tc while exercising in a hot , humid environment .
such surrogates are helpful in hot athletic or workplace environments when rectal , esophageal , and pbtc are not available .
however , care should be taken when practitioners select a tympanic or temporal measurement device as accuracy can vary . furthermore
, careful sport- and environment - specific validation of any individual device is prudent prior to heat illness mitigation in the field .
since temperature measurement is often used to reduce risk of heat - related illness during training and competition , use of the wrong device may increase one s risk of serious and possibly life - threatening complications .
the present findings have practical and clinically relevant implications providing athletes , coaches , and sports medicine practitioners with information to select an alternate measurement of tc to guard against heat - related illness .
 the accuracy of core temperature ( tc ) thermometry from temporal , tympanic , and oral thermometry devices has been variable during exercise in a hot , humid environment . 
 the purpose of the present study was to cross - validate temporal , two tympanic devices , and oral devices compared to an ingestible thermistor during exercise in a hot , humid environment . 
 fourteen young , active adults ( 6 women ) completed a graded exercise test until voluntary exhaustion in an environmental chamber ( 35.5  0.6 c , 53.9  5.8 % rh ) . 
 there was no statistical difference in mean temperature between tympanic device 1 and pill - based core temperature ( pbtc ) measurements across all time points and were positively correlated ( 0.357 ; p<0.001 ) . 
 temperatures of tympanic device 2 were statistically higher than pbtc ( 37.8  0.7 c vs. 37.6  1.0 c ; respectfully ) ( p=0.008 ) . at all time points , 
 temperatures for the second tympanic device and pbtc were positively correlated ( 0.192 ; p=0.043 ) . 
 temporal and pbtc values did not differ across time points and were positively correlated ( 0.262 ; p=0.005 ) across all time points . 
 mean oral temperature was significantly less than mean pbtc across all time points . 
 ( 37.0  0.4 c vs. 37.6  1.0 c , respectively ) ( p<0.001 ) . across all time points , oral and pbtc 
 were positively correlated ( 0.262 ; p=0.010 ) . tympanic and temporal devices can reflect tc while exercising in a hot , humid environment . 
 however , care should be taken when selecting the tympanic or temporal measurement device and validation is advised prior to heat illness mitigation in the field . 
INTRODUCTION
METHODS
Participants
Protocol
RESULTS
DISCUSSION