Inhaled L-menthol prolongs exercise in trained runners in a small trial

A trial in which each runner tested both conditions

The researchers studied nine women and nine men who practiced endurance running and had normal spirometry results. In this randomized, counterbalanced crossover trial, each participant completed the test with inhaled L-menthol and with a strawberry scent serving as a placebo.

The test involved running on a treadmill to exhaustion at 85% of the maximum speed reached during a previous cardiopulmonary exercise test. The researchers measured cardiorespiratory, metabolic and perceptual responses during exercise. The abstract consulted specifies neither the L-menthol dose nor the detailed administration procedure.

Longer exercise, with no detected increase in oxygen consumption

The average test duration was 445 seconds with L-menthol, compared with 406 seconds with the placebo. Perceived breathlessness was also lower with L-menthol during the test.

However, the researchers detected no difference between conditions in pulmonary ventilation, tidal volume, oxygen consumption, carbon dioxide production, oxygen saturation or heart rate. Breathing rate was lower with L-menthol.

These findings are consistent with breathing discomfort contributing to exercise limitation. They do not show that L-menthol improves oxygenation or increases cardiopulmonary capacity. Nor does the absence of a detected difference in a small sample demonstrate a complete absence of physiological effects.

What this finding does not yet support recommending

Lasting longer at a set speed until exhaustion is not the same as running faster over a given distance. This trial therefore cannot quantify any benefit in competition or establish a lasting improvement with repeated use.

The small sample and exclusively trained population limit generalizability. The abstract also does not allow an assessment of whether participants could recognize the two scents and anticipate their effects.

Finally, adverse effects, contraindications and the safety of repeated use are not documented in the available excerpt. This performance signal is not enough to make L-menthol inhalation a recommended practice.

What we can take away

Inhaled L-menthol appears capable of reducing breathlessness and prolonging intense exercise in trained runners. Benefits in competition and safety of use remain to be established.