Continuous thermoregulatory responses to mass-participation distance running in heat

Christopher Byrne, Jason Kai Wei Lee, Serena Ai Neo Chew, Chin Leong Lim, Elaine Yu Ming Tan
Medicine and Science in Sports and Exercise 2006, 38 (5): 803-10

PURPOSE: To continuously measure core temperature (T(c)) and heart rate(HR), and quantify fluid balance during a 21-km mass-participation road racein warm, humid environmental conditions.

METHODS: Eighteen heat-acclimatized male soldiers ingested a telemetric Tc sensor on the evening prior to the race and wore an ambulatory T(c) data recorder and HR 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.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(c) 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(c) 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.

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