Thermoregulatory responses during road races in hot-humid conditions at the 2019 Athletics World Championships

Purpose: To characterise thermoregulatory and performance responses of elite road-race athletes, while competing in hot, humid, night-time conditions during the 2019 IAAF World Athletic Championships. 

Method: Male and female athletes, competing in the 20 km racewalk (n=20 males, 24 females), 50 km racewalk (n=19 males, 8 females) and marathon (n=15 males, 22 females) participated. Exposed mean skin (Tsk) and continuous core body (Tc) temperature were recorded with infrared thermography and ingestible telemetry pill, respectively. 

Results: The range of ambient conditions (recorded roadside) were 29.3-32.7°C air temperature, 46-81 % relative humidity, 0.1-1.7 m∙s-1 air velocity and 23.5-30.6°C wet bulb globe temperature. Tc increased by 1.5 ± 0.1°C but mean Tsk decreased by 1.5 ± 0.4°C over the duration of the races. Tsk and Tc changed most rapidly at the start of the races and then plateaued, with Tc showing a rapid increase again at the end, in a pattern mirroring pacing. Performance times were between 3 to 20 % (mean = 113 ± 6%) longer during the championships compared to the personal best (PB) of athletes. Overall mean performance relative to PB was correlated with the wet-bulb globe temperature (WBGT) of each race (R2 = 0.89), but not with thermophysiological variables (R2 ≤ 0.3). 

Conclusion: As previously reported in exercise heat stress, in this field study Tc rose with exercise duration, whereas Tsk showed a decline. The latter contradicts the commonly recorded rise and plateau in laboratory studies at similar ambient temperatures, but without realistic air movement.