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 40 min constant-load exercise at 63% of maximum work rate followed by a 16.1 km time trial at 30 °C and 70% relative humidity. Temperature at rest was not different between the three methods of Tc measurement (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 between Tre and Tp measurements at any time throughout exercise (P=0.32). While there were no differences between Tre and Tty after 10 min (P=0.11) and 20 min (P=0.06) of exercise, Tty was lower than Tre after 30 min 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. Tty was significantly lower than Tre when 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.