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

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 °C). Method Ten male participants performed four time to exhaustion (TTE) trials on a cycle ergometer at 70% W max . 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. 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; η p 2 = 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.