The Effect Of Menthol Administered To The Stomach On Thermal Perception, Physiology, And Cycling Performance

PURPOSE: To examine how mentholated water administered directly to the stomach using nasogastric tubes may affect thermal perception, physiology and exercise performance, compared to regular ingestion. METHODS: On five separate occasions, eight participants (5 male, 3 female; 26 ± 5 y; 172 ± 8 cm; 73.13 ± 13.2 kg; 41.76 ± 8.69mlO2/kg/min) cycled at a steady-state for 60 minutes at 60% of their maximum oxygen consumption followed by a metrics-blinded, 15-minute, self-paced performance trial in a hot-humid environment (36.4 ± 0.6 °C and 52.6 ± 2.8% relative humidity). In four trials, participants had 3.2 ml/kg (~270 mL) of mentholated or plain water at 37 °C or 1 °C administered to the stomach using a nasogastric tube after 15, 30, 45, and 60 minutes of exercise. On a fifth occasion, participants drank an equivalent volume of cold-mentholated water. Whole body sweat loss (WBSL), rectal temperature (Tre),thermal sensation (TS; 0 = Neutral, 4 = Very Hot), exercise performance in kJ and heart rate (HR) were all measured and recorded. RESULTS: There was no difference in end-exercise Tre (38.6 ± 0.5 °C; p = 0.64), WBSL (0.805 ± 0.170 kg; p = 0.70), or mean HR (153 ± 14 bpm; p = 0.30) between trials. Compared to exercise performance with 37 °C water administration (147 ± 45 kJ), cold water administration with (157 ± 47 kJ; p = 0.02) or without menthol (158 ± 53 kJ; p = 0.02), as well as ingesting cold mentholated water (161 ± 52 kJ; p = 0.05) improved exercise performance, although mentholated 37 °C water administration did not (153 ± 47 kJ; p = 0.26). Compared with 37 °C water administration (2.4 ± 0.5), participants felt cooler with mentholated water administered at 37 °C (1.8 ± 0.7; p = 0.04) and 1 °C (1.6 ± 0.5; p = 0.02), as well as when ingested (1.6 ± 0.5; p = 0.03), and with 1 °C administered without menthol (1.8 ± 0.6; p = 0.01). CONCLUSIONS: Cold mentholated water did not affect physiological responses during exercise in the heat. However, cold water with or without menthol improved exercise performance in the heat. Meanwhile, water with menthol administered at either 37 °C or 1 °C improved thermal sensation. These findings suggest that different sensory pathways may be active for evoking perceptual, physiological, and behavioral/performance responses.