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°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°C (range 22.44–28.50°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°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°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.
Highlights
A triathlon race involves consecutive sequences of a 3.8 km swim, a 180 km cycle ride, and a 42.2 km run
All participants had a normal Tcore before the start of the competition; they reached a hyperthermic state during the marathon which persisted at least 1 h after completion of the race
Given the ACSM position stand about exertional heat illness during training and competition (Armstrong et al, 2007), the average wet bulb globe temperature (WBGT) during the event falls within a higher risk zone for all competitors, but especially for those who are incompletely acclimatized or possess inadequate fitness
Summary
A triathlon race involves consecutive sequences of a 3.8 km swim, a 180 km cycle ride, and a 42.2 km run. The Ironman triathlon has gained significant popularity in recent years. During the Ironman triathlon, participants compete for best overall race time, including timed transitions between the swimming, biking, and running legs. Laursen and colleagues demonstrated that during an Ironman triathlon recreational triathletes’ Tcore reached 38.1 ± 0.3°C (Laursen et al, 2006). Nybo and colleagues demonstrated that elevated core temperature alters prefrontal cerebral activity (Nybo and Nielsen, 2001). Hyperthermia (H) is defined as an elevation of core body temperature (Tcore) greater than 38.5°C. Exertional heat illness is a spectrum of conditions involving elevated body temperature; the two most serious of these conditions are heat exhaustion and exertional heat stroke (EHS). Core temperature is a critical vital sign in the assessment of a collapsed marathon runner who may have EHS (Ronneberg et al, 2008)
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