INTRODUCTION:
Exertional heat illnesses (EHI) pose a significant health risk in endurance sports for both amateur and elite athletes. While climate change exacerbates this risk during sporting events, exercise intensity remains a critical contributing factor. Investigating heat strain experienced by individuals is essential to understanding sport-specific risks and evaluating existing heat stress policies. This study reports the thermal strain of a heterogeneous cohort of amateur runners participating in 10 km (10KM), half-marathon (HM), and marathon (M) events in Hong Kong in February 2025. The aim was to differentiate heat strain across event lengths and identify modifying individual characteristics, such as age, sex, and body composition. We hypothesized that the greatest heat strain would occur in the 10KM event.
METHODS:
Seventy-six runners (age 38 ± 13 [18–65] years) ingested two telemetry pills to monitor core body temperature (TCORE); pill 1 before bed, and pill 2 upon waking on race day. Participants were distributed across 10KM (n=20, age=34.2 ± 14.3, 8 females, 12 males, body fat percentage [BF%] 23.0 ± 11.3%), HM (n=27, age=38.3 ± 13.0, 12 females, 15 males, BF% 19.4 ± 6.9%), and M (n=29, age=40.5 ± 10.8, 8 females, 21 males, BF% 15.6 ± 6.5%). Runners wore a heart rate monitor with attached skin temperature sensor. Portable weather stations (Pulse 4G-LTE, XM Weather, Greece) were positioned every 5 km along race routes. Races began between 05:30–08:30 and concluded by 14:00.
RESULTS:
Mean ambient temperature during the competition was 13.3 ± 1.6°C (range 10.0–20.8°C), with relative humidity of 36.9 ± 4.3% (22–50%), Wet Bulb Globe Temperature (WBGT) of 9.7 ± 3.7°C (5.7–25.9°C), solar irradiance of 113 ± 197 W/m² (0–798 W/m²), and wind speed of 0.7 ± 0.8 m/s (0–3.9 m/s). No cases of EHI were reported. Race durations (hours) were 01:00:49 ± 00:12:15 for 10KM (females: 01:00:00 ± 00:11:32; males: 01:01:14 ± 00:12:56), 01:58:44 ± 00:23:44 for HM (females: 02:02:26 ± 00:19:49; males: 01:56:09 ± 00:26:19), and 03:58:57 ± 00:36:52 for M (females: 04:05:53 ± 00:38:17; males: 03:56:25 ± 00:36:55). Starting TCORE was 37.5 ± 0.4°C (10KM), 37.7 ± 0.4°C (HM), and 37.4 ± 0.5°C (M), with finishing TCORE of 39.1 ± 0.6°C (+1.6 ± 0.7°C), 39.0 ± 0.6°C (+1.4 ± 0.6°C), and 38.5 ± 0.7°C (+1.1 ± 0.7°C), respectively. Peak finishing TCORE was 40.3°C (10KM), 40.2°C (HM), and 39.8°C (M). Changes in TCORE in females were 1.9 ± 0.6°C (10KM), 1.4 ± 0.6°C (HM), and 1.1 ± 0.7°C (M), compared to males: 1.4 ± 0.5°C (10KM), 1.3 ± 0.6°C (HM), and 1.1 ± 0.7°C (M).
CONCLUSION:
Significant environmental variability, particularly within solar irradiance and WBGT, was observed post-sunrise (circa 07:00) along the course. Single-point monitoring therefore fails to capture microclimate diversity. Greater changes in body temperature were generally observed in shorter events and in females. Further individual monitoring of varied athlete cohorts, combined with multi-location weather data, is necessary to enhance understanding of EHI risks in different sports for both amateur and elite athletes.