Inhaling cooler air reduces thermal, cardiorespiratory, and perceptual strain during prolonged exercise in the heat and extends exercise duration in young men.

OBJECTIVES

In hot environments, hyperthermia and the associated physiological and perceptual strain potentially limit prolonged exercise capacity. We tested the hypothesis that during prolonged exercise in the heat, lowering the temperature of inspired air would attenuate elevations in core temperature, cardiorespiratory strain, cerebral hypoperfusion, and perceptual stress, thereby enhancing exercise capacity.

DESIGN

Randomized crossover design.

METHODS

Twelve healthy males cycled at 50% of peak oxygen uptake in the heat (38 °C, 50% relative humidity) until esophageal temperature (an index of core temperature) reached 39.0 °C or volitional exhaustion. On two occasions, participants inhaled room air at 38 °C (control trial) or air gradually cooled from ~35 °C to ~28 °C (cooler-air trial) throughout exercise.

RESULTS

Exercise duration was 11.3 min longer in the cooler-air than the control trial (p = 0.004). Esophageal temperature and heart rate were 0.13-0.23 °C and 3.3-7.5 beats/min lower, respectively, in the cooler-air trial at 30-45 and 10-45 min of exercise (all p ≤ 0.011). Minute ventilation and thermal sensation were 1.3-5.8 L/min and 0.3-0.8 units lower, respectively, whereas end-tidal CO2 partial pressure was 1.2-2.3 mmHg higher in the cooler-air trial at 5-45 min of exercise (all p ≤ 0.012 for trial effects). Middle cerebral artery mean blood velocity did not differ between trials throughout exercise.

CONCLUSIONS

During prolonged exercise in the heat (38 °C), inhaling gradually cooled air from ~35 °C to ~28 °C reduces esophageal temperature, cardiorespiratory strain, and perceived thermal stress at corresponding time points in the ambient air inhalation and enhances exercise capacity.