Core Temperature Response During the Marathon Portion of the Ironman World Championship (Kona-Hawaii)

Abstract

The Ironman triathlon consists of a 3.8 km swim, 180 km bike, and 42.195 km run. Thermoregulation responses play an important role in performance optimization and injury prevention. Factors such as environmental conditions including heat and humidity, athlete training level, and race duration can affect thermoregulation. Hyperthermia occurs when the core temperature rises above 38.5 degrees C. The present study aims to describe core temperature (Tcore) in top-level and well-trained age group triathletes during the marathon of Ironman World Championship 2014 in Kona-Hawaii under thermal stress conditions. Tcore of 15 triathletes (age: 36.11 +/- 7.36 years, body mass: 71.14 +/- 7.12 kg, height: 179 +/- 0.04 cm, and fat %: 8.48 +/- 0.85) who classified for the Ironman World Championship was measured by an ingestible pill telemetry system prior to competition, during the marathon and 60 min after finishing the race. Mean wet bulb globe temperature (WBGT) during the marathon was 24.66 degrees C (range 22.44-28.50 degrees C). Body mass index (BMI) and perceived exertion (Borg Scale and Visual Analog Scale-Pain) were collected before the race and 60 min after the event. Time variables were extracted from their official race time and split times. Finish time was 10: 06:56 +/- 0:48:30. Tcore was initially 36.62 +/- 0.17 degrees C, increased at the end of the event (38.55 +/- 0.64; p < 0.01) and remained elevated 60 min after the event (38.65 +/- 0.41 degrees C; p < 0.002). BMI significantly decreased after the event (22.85 +/- 1.11 vs. 21.73 +/- 1.36; p < 0.05), whereas both exercise perceived exertion [Borg Scale (10.2 +/- 1.64 vs. 18.60 +/- 1.67; p < 0.003)] and perceived muscle pain [VAS Pain (2.75 +/- 1.59 vs. 9.08 +/- 1.13; p < 0.001)] increased significantly after the event. Tcore during competition correlated negatively with position in age group (r - 0.949, p = 0.051), but not with race time (r = -0.817; p = 0.183). High-level age group triathletes competing under thermal stress conditions in the Kona Ironman reached a state of hyperthermia during the marathon. After 60 min of recovery the hyperthermia persisted. Strategies to aid post-event cooling and recovery should be considered to avoid the potentially dangerous adverse health effects of hyperthermia.