The unique stress of an Ironman triathlon involving a 2.4 mile swim, 112 mile bike, and 26.2 mile run leads to extreme yet variable physiological and biochemical stress. Thermoregulatory responses during ultra-endurance exercise are often limited to measurements before and after exercise, warranting further investigation of repeated monitoring of the thermoregulatory demands imposed on the body during this event. Objective: Observe the response of gastrointestinal temperature (Tgi) in triathletes during a full Ironman distance triathlon race. Design: Observational field study. Setting: 2012 Lake Placid Ironman Triathlon (WBGT= 22.1 ± 2.0°C). Patients or Other Participants: Ironman triathletes participating in the 2012 Lake Placid Ironman (n=27; age=39.9 ± 8.0y; height=174 ± 11cm; body mass=73.1 ± 9.6kg; body fat=15.13 ± 6.19%). Interventions: All participants took an ingestible temperature sensor the evening before the Ironman race. Tgi was recorded via handheld receiver before the race (PRE), during the swim-to-bike transition (T1), during the bike-to-run transition (T2), and immediately following the race (POST). Data were analyzed via oneway ANOVA and are presented as mean ± standard deviation. Additionally, a Pearson correlation was performed to examine the relationship between delta (POSTPRE) thermoregulatory response ( ˜ Tgi) and finish time. Significance level was set a priori at p<0.05. Main Outcome Measures: Tgi finish time. Results: Mean finish time was 790.26 ± 87.01min. Mean Tgi at PRE (n=27), T1 (n=16), T2 (n=25), and POST (n=27) were 37.39 ± 0.34°C, 38.06 ± 0.42°C, 38.27 ± 0.28°C, and 38.42 ± 0.55°C, respectively. Tgi was significantly higher from PRE to POST race (1.03 ± 0.6°C; p<0.001). Additionally, Tgi was significantly elevated at T1 and T2 compared to PRE (p<0.001), while Tgi was also significantly higher at POST compared to T1 (p=0.037). Pearson correlation revealed no significant interaction between ˜Tgi and finish time (r= -0.17, p>0.05) Conclusions: Ironman competitors are a unique cohort of athletes who are exposed to extreme physiological demands due to the ultra-endurance nature of their sport. In-race monitoring provided an enhanced understanding of the thermoregulatory response to the Ironman race. The Ironman event resulted in a significantly higher Tgi at all time points compared to prerace measurements, while Tgi was not correlated to finish time. Additionally, likely due to the intense biomechanical nature and prolonged exposure to environmental conditions, the combined bike and run portions of the race resulted in a further increase in Tgi. However, despite being exposed to physical, environmental, nutritional, and biochemical stressors that resulted in mild hyperthermia, the participants were able to avoid a detrimental rise in Tgi and potential of a subsequent heat illness that is commonly seen in higher intensity exercise.
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