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

PURPOSE: This study aimed 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 the 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°C ± 0.7°C) than 16 (39.0°C ± 0.45°C), 30 (38.8°C ± 0.3°C), and 44 km·h -1 (38.8°C ± 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 bpm higher in still air than 44 km·h -1 ( P = 0.035). RPE 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 because of modest improvements in evaporative efficiency.

The effect of minimal differences in the skin-to-air vapor pressure gradient at various dry-bulb temperatures on self-paced exercise performance.

The effects of dry-bulb temperature on self-paced exercise performance, along with thermal, cardiovascular, and perceptual responses, were investigated by minimizing differences in the skin-to-air vapor pressure gradient (Psk,sat - Pa) between four temperatures. Fourteen trained male cyclists performed 30-km time trials in 13°C and 44% relative humidity (RH), 20°C and 70% RH, 28°C and 78% RH, and 36°C and 72% RH. Power output was similar in 13°C (275 ± 31 W; means and SD) and 20°C (272 ± 28 W; P = 1.00), lower in 36°C (228 ± 36 W) than 13°C, 20°C, and 28°C (262 ± 27 W; P < 0.001) and lower in 28°C than at 13°C and 20°C (P < 0.001). Peak rectal temperature was higher in 36°C (39.6 ± 0.4°C) than in all conditions (P < 0.001) and higher in 28°C (39.1 ± 0.4°C) than 13°C (38.7 ± 0.3°C; P < 0.001) and 20°C (38.8 ± 0.3°C; P < 0.01). Mean heart rate was higher in 36°C (163 ± 14 beats·min-1) than all conditions (P < 0.001) and higher in 20°C (156 ± 11 beats·min-1; P = 0.009) and 28°C (159 ± 11 beats·min-1; P < 0.001) than 13°C (153 ± 11 beats·min-1). Mean cardiac output was lower in 36°C (16.8 ± 2.5 L·min-1) than all conditions (P < 0.001) and lower in 28°C (18.6 ± 1.6 L·min-1) than 20°C (19.4 ± 2.0 L·min-1; P = 0.004). Ratings of perceived exertion were higher in 36°C than all conditions (P < 0.001) and higher in 28°C than 20°C (P < 0.04). Self-paced exercise performance was maintained in 13°C and 20°C at a matched evaporative potential, impaired in 28°C, and further compromised in 36°C in association with a moderately lower evaporative potential and marked elevations in thermal, cardiovascular, and perceptual strain.NEW & NOTEWORTHY This is the first study to investigate the effects of dry-bulb temperature (13, 20, 28, and 36°C) on self-paced exercise performance by minimizing differences in the skin-to-air vapor pressure gradient (i.e., evaporative potential) between conditions. Performance was similar in 13°C and 20°C with a matched evaporative potential, whereas it was reduced at 28°C and further impaired at 36°C in association with a large decrease in dry heat loss and moderate reduction in evaporative potential.

Self-paced exercise performance in the heat with neck cooling, menthol application, and abdominal cooling.

OBJECTIVES: To investigate whether the exercise performance benefits with neck cooling in the heat are attributable to neck-specific cooling, general body cooling, a cooler site-specific thermal perception or a combination of the above. DESIGN: Counter-balanced crossover design. METHODS: Twelve healthy participants cycled in the heat (34°C, 30% relative humidity), at a power output (PO) self-selected to maintain a fixed rating of perceived exertion (RPE) of 16. Each participant underwent four experimental trials: no cooling (CON), neck cooling (NEC), abdominal cooling (ABD), or neck cooling with menthol (MEN). Participants cycled for 90min or until their workload reduced by <70% of their initial PO. Changes in PO, rectal temperature (Tre), mean skin temperature (Tsk), whole-body thermal sensation (TSwb) and thermal sensation of the neck (TSneck) were recorded throughout. RESULTS: The mean reduction in PO throughout exercise was similar (p=0.431) for CON (175±10W), NEC (176 ±12W), ABD (172±13W) and MEN (174±12W). The ΔTre at the end of exercise was similar (p=0.874) for CON (0.83±0.5°C), NEC (0.85±0.5°C), ABD (0.82±0.5°C) and MEN (0.81±0.5°C). TSwb was cooler (p<0.013) in MEN (125±8mm) compared to CON (146±19mm), NEC (135±11mm) and ABD (141±16mm). CONCLUSIONS: No differences in exercise performance or thermal strain were observed in any of the cooling trials compared to the CON trial, despite significantly cooler TSwb values in the MEN and NEC trials compared to the CON trial. These findings differ from previous observations and highlight that the benefit of neck cooling may be situation dependent.