Telemetry pill versus rectal and esophageal temperature during extreme rates of exercise-induced core temperature change

Core temperature measurement with an ingestible telemetry pill has been scarcely investigated during extreme rates of temperature change, induced by short high-intensity exercise in the heat. Therefore, nine participants performed a protocol of rest, (sub)maximal cycling and recovery at 30 degrees C. The pill temperature (T-pill) was compared with the rectal temperature (T-re) and esophageal temperature (T-es). T-pill corresponded well to T-re during the entire trial, but deviated considerably from T-es during the exercise and recovery periods. During maximal exercise, the average Delta T-pill-T-re and Delta T-pill-T-es were 0.13 +/- 0.26 and - 0.57 +/- 0.53 degrees C, respectively. The response time from the start of exercise, the rate of change during exercise and the peak temperature were similar for T-pill and T-re. T-es responded 5 min earlier, increased more than twice as fast and its peak value was 0.42 +/- 0.46 degrees C higher than T-pill. In conclusion, also during considerable temperature changes at a very high rate, T-pill is still a representative of T-re. The extent of the deviation in the pattern and peak values between T-pill and T-es (up to > 1 degrees C) strengthens the assumption that T-pill is unsuited to evaluate central blood temperature when body temperatures change rapidly.