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

The purpose of this study was to characterize thermoregulatory and performance responses of elite road-race athletes, while competing in hot, humid, night-time conditions during the 2019 IAAF World Athletic Championships. 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 infra-red thermography and ingestible telemetry pill, respectively. The range of ambient conditions (recorded roadside) was 29.3 degrees C-32.7 degrees C air temperature, 46%-81% relative humidity, 0.1-1.7 m center dot s-1 air velocity, and 23.5 degrees C-30.6 degrees C wet bulb globe tem-perature. Tc increased by 1.5 +/- 0.1 degrees C but mean Tsk decreased by 1.5 +/- 0.4 degrees 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 mir-roring pacing. Performance times were between 3% and 20% (mean = 113 +/- 6%) longer during the championships compared with the personal best (PB) of athletes. Overall mean performance relative to PB was correlated with the wet-bulb globe tem-perature (WBGT) of each race (R2 = 0.89), but not with thermophysiological variables (R2 < 0.3). 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.NEW & NOTEWORTHY This paper provides a kinetic observation of both core and skin temperatures in 108 elite athletes, dur-ing various outdoor competition events, adding to the very limited data so far available in the literature taken during elite com-petitions. The field skin temperature findings contrast previous laboratory findings, likely due to differences in relative air velocity and its impact on the evaporation of sweat. The rapid rise in skin temperature following cessation of exercise highlights the im-portance of infrared thermography measurements being taken during motion, not during breaks, when being used as a mea-surement of skin temperature during exercise.