Influence of Air Velocity on Self-Paced Exercise Performance in Hot Conditions

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.