Validity of the CORE Wearable Sensor During Internal Cooling Induced by Hyperhydration with Cold Water at Rest.

Pre-exercise internal cooling through cold-water-induced hyperhydration may attenuate increases in core body temperature (TC) and improve endurance performance. Quantifying the extent of reduction in TC induced by hyperhydration is important for optimizing its timing before exercise. We compared TC values obtained from a wearable sensor, the CORE, with those of a gastrointestinal temperature telemetric sensor (GTS) during hyperhydration. Eleven participants (two women; age: 24 ± 4 yrs) completed a 120 min seated period where they consumed, over the first 60 min, four boluses of 4 °C water (7.5 mL · kg fat-free mass [FFM]-1), each containing 0.35 g · kg FFM-1 of glycerol. Measures of TC were taken every 20 min with both sensors. According to the GTS, hyperhydration induced a peak TC decline of -0.76 ± 0.31 °C at min 60; at this time, the change in TC from baseline estimated by the CORE was -0.09 °C ± 0.20 °C. The greatest decline in TC detected by the CORE was -0.11 ± 0.19 °C. Bland and Altman analyses revealed that average TC declines of -0.1, -0.2, -0.3, -0.4, -0.5 and -0.6 °C from baseline were associated with TC values estimated by the CORE that were respectively +0.29, +0.41, +0.57, +0.65, +0.77 and +0.89 °C higher than the GTS. An intraclass correlation coefficient of 0.12 suggested poor agreement between instruments. These results raise concerns about the ability of the CORE to detect changes in TC induced by a hyperhydration protocol generating a substantial heat sink.