Author(s): AGER, L.,MJEFFRIES, O., Institution: NEWCASTLE UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 2392

INTRODUCTION:
Convective airflow facilitates human thermoregulation in ambient temperatures (Tamb) typically below skin temperature (Tsk) (~35°C) during exercise and at rest. In higher temperatures, as typified during extreme heat wave scenarios, it is unclear how convective airflow exceeding Tsk may impact the maintenance of body core temperature during exercise. The aim of this study was to examine conductive airflow in extreme temperatures to aid our understanding of thermal, cardiovascular and perceptual strain during exercise.
METHODS:
Thirteen trained, non-heat acclimated males [age 30±6 years; body mass 73.3±7.8 kg; height 181.4±5.1 cm; peak oxygen uptake 61.5±5.1 ml kg-1 min-1; peak power output (PPO) 412±36 W] completed four separate 30-min cycling bouts at 50% PPO in four differing environmental conditions: 37°C and 45°C each with (37F, 45F) and without (37NF, 45NF) dual fan-assisted airflow (~3 m.s-1). Cardiovascular measures of rectal core temperature (Tc), mean Tsk, heart rate (HR) and oxygen consumption were recorded continuously. Perceptual measures of Relative Perceived Exertion and Thermal Sensation were recorded every 3-min. Whole Body Sweat Loss (WBSL) was estimated from pre vs post body mass. A two-way repeated measures ANOVA was performed to identify differences between trials. Statistical significance was set at P<0.05.
RESULTS:
Tc was different between conditions (P = 0.022), changed with time (P<0.001) and showed an interaction effect (P<0.001). During the latter stages of exercise, we observed the change from baseline in 37NF was 15% greater than 37F, and 45NF was 12.5% greater than 47F. WBSL was different between conditions (P<0.001), being greater with respect to Tamb in 45NF vs 37NF (+33%, P=0.007) and 45F vs 37F (+35%, P = 0.008). However, WBSL did not differ (<6% difference) in similar Tamb irrespective of fan, between 37NF vs 37F (P = 0.752) and 45NF vs 45F (P = 0.752). Cardiovascular strain indicated by HR differed by condition (P = 0.001), temporally (P<0.001), and showed an interaction effect (P<0.001). Mean HR was greater during 37NF vs 37F (+7 bpm, P = 0.07), however this difference was not evident in higher temperatures 45NF vs 45F (+4 bpm, P = 0.150). HR was greater during 45NF vs 37NF (+10 bpm, P<0.001) and 45F vs 37F (+13 bpm, P<0.001).
CONCLUSION:
Convective airflow during exercise in 37°C Tamb reduced thermal, cardio and perceptual strain. In more extreme temperatures where Tamb exceed Tsk (Tamb 45°C), airflow did not result in greater heat storage and instead amplified heat loss. Interestingly these differences were not supported by changes in WBSL. Our data suggests that even at higher Tamb, the addition of airflow promotes evaporative potential and sweat efficiency sufficiently to offset the increase in dry heat transfer gain. In conditions of low humidly (30%) our findings provide clear evidence for the use of conductive airflow during exercise to improve thermal tolerance and mitigate heat illness risk in extreme temperatures up to 45°C.