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 elevations in mean body temperature

Purpose 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 oC). Method Ten male participants performed four time to exhaustion (TTE) trials on a cycle ergometer at 70 % Wmax. In a randomized crossover design, 1) placebo flavoured 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 temperatures, heart rate, rating of perceived effort, thermal comfort and thermal sensation were recorded. Results 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; ηp2 = 0.260). Conclusion 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.