Core-temperature sensor ingestion timing and measurement variability

Context: Telemetric core-temperature monitoring is becoming more widely used as a noninvasive means of monitoring core temperature during athletic events. Objective: To determine the effects of sensor ingestion timing on serial measures of core temperature during continuous exercise. Design: Crossover study. Setting: Outdoor dirt track at an average ambient temperature of 4.4°C ± 4.1°C and relative humidity of 74.1% ± 11.0%. Patients or Other Participants: Seven healthy, active participants (3 men, 4 women; age = 27.0 ± 7.5 years, height 5 172.9 ± 6.8 cm, body mass = 67.5 ± 6.1 kg, percentage body fat = 12.7% ± 6.9%, peak oxygen uptake [V̇O_2peak] = 54.4 ± 6.9 mLNkg21Nmin21) completed the study. Intervention(s): Participants completed a 45-minute exercise trial at approximately 70% V̇O_2peak. They consumed coretemperature sensors at 24 hours (P1) and 40 minutes (P2) before exercise. Main Outcome Measure(s): Core temperature was recorded continuously (1-minute intervals) using a wireless data logger worn by the participants. All data were analyzed using a 2-way repeated-measures analysis of variance (trial × time), Pearson product moment correlation, and Bland-Altman plot. Results: Fifteen comparisons were made between P1 and P2. The main effect of time indicated an increase in core temperature compared with the initial temperature. However, we did not find a main effect for trial or a trial × time interaction, indicating no differences in core temperature between the sensors (P1 = 38.3°C ± 0.2°C, P2 = 38.3°C ± 0.4°C). Conclusions: We found no differences in the temperature recordings between the 2 sensors. These results suggest that assumed sensor location (upper or lower gastrointestinal tract) does not appreciably alter the transmission of reliable and repeatable measures of core temperature during continuous running in the cold.