Rectal, telemetry pill and tympanic membrane thermometry during exercise heat stress

We compared the accuracy of an ingestible telemetry pill method of core temperature (Tc) measurement and an infrared tympanic membrane thermometer to values from a rectal thermistor during exercise-induced heat stress. Ten well-trained subjects completed four exercise trials consisting of 40min constant-load exercise at 63% of maximum work rate followed by a 16.1km time trial at 30°C and 70% relative humidity. Temperature at rest was not different between the three methods ofTcmeasurement (Tre: 37.2±0.3°C;Tp: 37.2±0.2°C;Tty: 37.1±0.3°C;P=0.40). Temperature rose continuously during the exercise period (ΔTre: 2.2±0.5°C; ΔTp: 2.2±0.5°C; ΔTty: 1.9±0.5±°C and there were no differences betweenTreandTpmeasurements at any time throughout exercise (P=0.32). While there were no differences betweenTreandTtyafter 10min (P=0.11) and 20min (P=0.06) of exercise,Ttywas lower thanTreafter 30min of exercise (P<0.01) and remained significantly lower throughout the remainder of the exercise period. These results demonstrate that the telemetry pill system provides a valid measurement of trunk temperature during rest and exercise-induced thermal strain.Ttywas significantly lower thanTrewhen temperature exceeded 37.5°C. However, whether these differences are due to selective brain cooling or imperfections in the tympanic membrane thermometer methodology remains to be determined.