Assessing core body temperature in a cool marathon using two pill ingestion strategies

Objectives The purpose was to directly assess in-competition thermoregulatory responses in recreational runners during a city marathon conducted in cool, ambient conditions using a two-pill ingestion strategy. Methods Thirty-two recreational runners (age: 38.7 ± 10.2 years, mass: 73.9 ± 11.0 kg, height: 177 ± 8 cm) were invited to participate in this study. Core temperature was continuously assessed using telemetric ingestible pills. Each runner swallowed two pills: the first pill (Pill 1) 11 h:47 min ± 1 h:01 min pre-race (before overnight sleep) and the second (Pill 2) 2 h:35 min ± 0 h:54 min pre-race (on wakening). Results Pre-race core temperature for Pill 1 was significantly different from Pill 2, with values of 37.4 ± 0.4 °C and 37.1 ± 0.6 °C, respectively (p=0.006). The mean core temperature during the race was higher for Pill 1 compared to Pill 2 (38.5 ± 0.5 °C and 37.8 ± 1.0 °C, respectively; p<0.001). Peak core temperature was higher for Pill 1 compared to Pill 2 (39.1 ± 0.5 °C and 38.8 ± 0.5 °C, respectively; p=0.03). Post-race core temperature was higher for Pill 1 compared to Pill 2 (38.8 ± 0.7 °C and 38.1 ± 1.3 °C, respectively; p=0.02). Conclusions The timing of pill ingestion significantly impacted core temperature and hence timing of pill ingestion should be standardised (5 h:30 min–7 h prior to measurement). Despite the relatively cool ambient conditions during the race, a significant number of runners achieved a high core body temperature (≥39 °C), which was not accompanied by any signs of heat illness.