Objectives: Core temperature (TCORE), skin temperature (TTORSO) and running kinematics were measured across different athlete categories at a World Cup Sprint Triathlon, occurring during a heatwave (~ 25-31 °C Wet Bulb Globe Temperature [WBGT]). Methods: Sixty-six triathletes participated: 21 World Cup (7 females), 32 Hong Kong-Elite (HK-Elite; 8 females) and 13 Amateur (6 females). Results: Seventeen triathletes displayed a TCORE > 40.0 °C and two > 41.0 °C. Peak TCORE was not different between athlete categories (World Cup: 39.7 ± 0.6 °C; HK-Elite: 39.9 ± 0.8 °C; Amateur: 39.5 ± 0.8 °C; p = 0.357). However, there was an interaction between race phase and category (p = 0.001). Changes in TCORE for World Cup (2.4 ± 0.4 °C) and HK-Elite (2.5 ± 1.0 °C) were greater than for Amateurs (1.5 ± 0.7 °C). Peak TTORSO was higher in HK-Elites during afternoon races compared with morning World Cup races (p < 0.001). TTORSO reduced during the swim (pbonf < 0.001), then increased during the bike (pbonf < 0.001) but not run (pbonf = 1.00). World Cup athletes (3.15 ± 0.23 m) displayed longer strides (HK-Elites: 2.64 ± 0.35 m; Amateurs: 2.18 ± 0.30 m; pbonf < 0.001), shorter contact times (209.3 ± 13.7 ms; HK-Elites: 237.8 ± 23.0 ms; Amateurs: 262.9 ± 31.0 ms, pbonf < 0.001) and higher stride frequency (182.9 ± 6.3 strides.min-1) than HK-Elites (173.9 ± 6.8 strides.min-1) and Amateurs (173.2 ± 8.7 strides.min-1, pbonf < 0.001), which were comparable. There were no biomechanical changes over time and no interactions. Conclusion: Different athlete categories displayed comparable peak TCORE responses. Amateur triathletes tolerated TCORE > 40.0 °C without heat illness symptoms. TCORE may rise > 41 °C during a sprint triathlon held under Blue flag conditions (~ 26 °C WBGT), questioning the suitability of sprint-distance triathlons as a safer alternative to Olympic-distance triathlons under Red/Black flag conditions (> 30.1 °C WBGT). Key Points 1. Mitigating the risks of exertional heat illness remains a major challenge for event organisers of large sporting competitions, which often include amateur through to professional participants. How athletes of different training status respond at the same event is unclear. 2. The presentation of core temperatures > 40 °C appears to be independent of athlete level. Extreme body temperatures (2 individuals > 41 °C) occurred during a sprint triathlon, which is a stated modification purported to lower risk for Olympic-distance triathlon. 3. Reducing triathlon events to a sprint distance may not sufficiently reduce the risk of heat illness, earlier start times may be a more suitable strategy.
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