Dyspnea Reduction With L-Menthol Inhalation Improves High-Intensity Endurance Running Performance in Healthy Trained Adults.

Dyspnea occurs during high-intensity running in healthy trained individuals and may limit endurance performance. Given that L-menthol inhalation can alleviate dyspnea in other contexts, we investigated whether L-menthol inhalation reduces dyspnea and improves endurance performance during high-intensity running in healthy trained individuals. Nine females (mean ± standard deviation; V ˙ O2peak = 55.8 ± 6.8 mL/kg/min) and nine males ( V ˙ O2peak = 60.3 ± 4.6 mL/kg/min) endurance runners with normal spirometry completed a randomized crossover counterbalanced trial with L-menthol inhalation or a strawberry scent (placebo). Performance was measured with a treadmill time-to-exhaustion (TTE) test at 85% of the peak velocity achieved during a preliminary cardiopulmonary exercise test. Cardiorespiratory, metabolic, and perceptual responses were measured throughout. Compared with the placebo, L-menthol inhalation reduced dyspnea across the TTE test (∼1 AU; p = 0.004) and extended the TTE test duration (406 ± 94 vs. 445 ± 106 s; p = 0.009). Pulmonary ventilation (p = 0.377), tidal volume (p = 0.298), O2 consumption (p = 0.277), CO2 production (p = 0.786), pulse O2 saturation (p = 0.766), and heart rate (p = 0.974) did not differ between conditions. Breathing frequency was lower with L-menthol inhalation than with placebo (p = 0.045). L-menthol inhalation attenuated dyspnea and enhanced high-intensity running endurance performance without substantial changes in cardiorespiratory and metabolic responses to exercise. These results suggest that dyspnea constitutes an important constraint on endurance performance during high-intensity running in healthy trained individuals, and identify acute L-menthol inhalation as an effective ergogenic strategy for this exercise modality and population. TRIAL REGISTRATION: Registered at the Brazilian Registry of Clinical Trials (U1111-1289-3438).