LAUSR

PURPOSE To determine the effect of different air velocities on heat exchange and performance during prolonged self-paced exercise in the heat. METHODS Twelve male cyclists performed a 700-kJ time trial in four different air velocity conditions (still air, 16, 30 and 44 km·h-1) in 32 °C and 40% relative humidity. Performance, thermal, cardiovascular and perceptual responses were measured, and heat balance parameters were estimated using partitional calorimetry, including the maximum potential for sweat evaporation (Emax). RESULTS Mean power output was lower in still air (232 ± 42 W) than 16 (247 ± 30 W), 30 (250 ± 32 W) and 44 km·h-1 (248 ± 32 W; all P < 0.001), but similar between 16, 30 and 44 km·h-1 air velocity conditions (P ≥ 0.275). Emax was lower in still air (160 ± 13 W·m-2) than 16 (298 ± 25 W·m-2), 30 (313 ± 23 W·m-2) and 44 km·h-1 (324 ± 31 W·m-2), and lower in 16 than 44 km·h-1 (all P < 0.001). Peak core temperature was higher in still air (39.4 ± 0.7 °C) than 16 (39.0 ± 0.45 °C), 30 (38.8 ± 0.3 °C) and 44 km·h-1 (38.8 ± 0.5 °C; all P ≤ 0.002). Mean skin temperature was lower with greater airflow (P < 0.001), but similar in 30 and 40 km·h-1 (P = 1.00). Mean heart rate was ~2 beats·min-1 higher in still air than 44 km·h-1 (P = 0.035). Rating of perceived exertion was greater in still air than 44 km·h-1 (P = 0.017). CONCLUSIONS Self-paced cycling in still air was associated with a lower Emax and subsequently higher thermal strain, along with a similar or greater cardiovascular strain, despite work rate being lower than in conditions with airflow. The similarity in performance between the 16, 30 and 44 km·h-1 air velocity conditions suggests that airflow ≥16 km·h-1 does not further benefit self-paced exercise performance in the heat, due to modest improvements in evaporative efficiency.