Continuous thermoregulatory responses to mass-participation distance running in heat

Purpose: To continuously measure core temperature (T,) and heart rate (HR). and quantify fluid balance during a 21-km mass-participation road race in warm. humid environmental conditions. Methods: Eighteen heat-acclimatized male soldiers ingested a telemetric T, sensor on the evening prior to the race and wore an ambulatory T, data recorder and FIR monitor during the race. Pre- to postrace changes in nude body mass quantified fluid balance. Results: Environmental wet bulb globe temperature averaged 26.5 degrees C. All runners finished the race asymptomatic of heat illness in a mean +/- SD (range) time of 118 +/- 13 (105-146) min, corresponding to an average running speed of 10.8 +/- 1. 1 (8.6-12.0) km center dot h(-1) All runners recorded peak T-c > 39 degrees C- 56% (N = 10) > 40 degrees C: and 11% (N = 2) > 41 degrees C. Peak T-c was 40.1 +/- 0.7 (39.3-41.7) degrees C at 86 +/- 36 (13-130) min, with T-c 39.9 +/- 0.8 (38.3-41.7) degrees C at race finish. The magnitude of T, response was unrelated (P > 0.05) to running time or fluid balance (e.g.. fluid intake. % dehydration). Cumulative heat strain index was 2790 1112 (1046-5144) units at race finish. Conclusion: Ingestible telemetric temperature sensors demonstrated utility for continuous measurement of T, during mass-participation running. Successful application of this technology has highlighted the magnitude and duration of T-c elevation that runners will voluntarily achieve during mass-participation distance races in heat and high humidity without medical consequence.