l-Menthol mouth rinse or ice slurry ingestion during the latter stages of exercise in the heat provide a novel stimulus to enhance performance despite elevation in mean body temperature

Owen Jeffries, Matthew Goldsmith, Mark Waldron

This study investigated the effects of L-menthol mouth rinse and ice slurry ingestion on time to exhaustion, when administered at the latter stages (~ 85%) of baseline exercise duration in the heat (35 °C). Ten male participants performed four time to exhaustion (TTE) trials on a cycle ergometer at 70% Wmax. In a randomized crossover design, (1) placebo-flavored non-calorific mouth rinse, (2) L-menthol mouth rinse (0.01%), or (3) ice ingestion (1.25 g kg-1), was administered at 85% of participants' baseline TTE. Time to exhaustion, core and skin temperature, heart rate, rating of perceived effort, thermal comfort and thermal sensation were recorded. From the point of administration at 85% of baseline TTE, exercise time was extended by 1% (placebo, 15 s), 6% (L-menthol, 82 s) and 7% (ice, 108 s), relative to baseline performance (P = 0.036), with no difference between L-menthol and ice (P > 0.05). Core temperature, skin temperature, and heart rate increased with time but did not differ between conditions (P > 0.05). Thermal sensation did not differ significantly but demonstrated a large effect size (P = 0.080; [Formula: see text] = 0.260). These results indicate that both thermally cooling and non-thermally cooling oral stimuli have an equal and immediate behavioral, rather than physiological, influence on exhaustive exercise in the heat.