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Randomized Controlled Trial
. 2018 Nov;118(11):2435-2442.
doi: 10.1007/s00421-018-3970-4. Epub 2018 Aug 20.

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  1   2 , Matthew Goldsmith  3 , Mark Waldron  3   4
Affiliations
Randomized Controlled Trial

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 et al. Eur J Appl Physiol. 2018 Nov.

Abstract

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% 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.

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; [Formula: see text] = 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.

Keywords: Heat; Ice slurry; Menthol; Perception; TTE; Thermoregulation.

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Conflict of interest statement

None reported.

Figures

Fig. 1
Fig. 1
Time to exhaustion following administration of placebo, menthol and ice conditions at 85% of baseline time to exhaustion. Exercise time from the point of administration (21.02 ± 3.53 min) is shown, placebo (black), menthol mouth rinse (gray) ice slurry ingestion (white). All data are shown as mean ± SD, (n = 10)
Fig. 2
Fig. 2
a Core temperature (°C) and b mean skin temperature (°C) following administration of placebo, menthol and ice slurry conditions at 85% of baseline time to exhaustion. Placebo (black), menthol mouth rinse (gray) ice slurry ingestion (white). All data are shown as mean ± SD, (n = 10)
Fig. 3
Fig. 3
a Rating of thermal comfort and b thermal sensation following administration of placebo, menthol and ice slurry conditions at 85% of baseline time to exhaustion. Placebo (black), menthol mouth rinse (gray) ice slurry ingestion (white). All data are shown as mean ± SD, (n = 10)
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