L-menthol administration facilitates breathing comfort during exhaustive endurance running and improves running capacity in well-trained runners: A randomized crossover study

This study aimed to clarify the contribution of L-menthol administration to endurande exercise capacity. Thirteen male runners (age, 35.8 +/- 7.8 years; peak oxygen uptake, 62.7 +/- 6.8 mL kg(-1) min(-1)) ran on treadmills at fixed intensities of their anaerobic thresholds to exhaustion. All participants underwent three trials-water ingestion (W-IG), L-menthol mouth rinsing (M-MR), and L-menthol ingestion (M-IG)- in a random order every 5 min while running. Breathing comfort (BC) was measured immediately after fluid intake. Dyspnea threshold against external inspiratory resistance was examined before and after the running test. The running time with M-IG (1683.9 +/- 520.3 s) was longer than that with W-IG (1410.2 +/- 465.9 s, effect size [ES] = 0.55). BC with M-IG (2.00 +/- 0.74) was higher than that with W-IG (0.42 +/- 0.79) at exhaustion (ES > 2.00). The dyspnea threshold after running decreased to 19.2 +/- 7.6 cm H2O L-1 s(-1) with W-IG, whereas that with M-MR (26.2 +/- 6.5 cm H2O L-1 s(-1)) and M-IG (29.2 +/- 2.8 cm H2O L-1 s(-1)) remained high (p for interaction < 0.001). M-IG facilitated BC during running, improved endurance capacity, and prevented decreases in the dyspnea threshold against external inspiratory resistance after exhaustive running.

Automated summary

This study aimed to investigate the effects of L-menthol on endurance exercise capacity. The results showed that L-menthol administration can prolong running time and improve breathing comfort. Additionally, L-menthol can prevent the decrease in dyspnea threshold after running.