Mouth rinsing and ingesting salty or bitter solutions does not influence corticomotor excitability or neuromuscular function.

ABSTRACT

PURPOSE: To explore the effect of tasting unpleasant salty or bitter solutions on lower limb corticomotor excitability and neuromuscular function. METHODS: Nine females and eleven males participated (age 27 ± 7 years, BMI 25.3 ± 4.0 kg m-2). Unpleasant salty (1 M) and bitter (2 mM quinine) solutions were compared to water, sweetened water, and no solution, which functioned as control conditions. In a non-blinded randomized cross-over order, each solution was mouth rinsed (10 s) and ingested before perceptual responses, instantaneous heart rate (a marker of autonomic nervous system activation), quadricep corticomotor excitability (motor-evoked potential amplitude) and neuromuscular function during a maximal voluntary contraction (maximum voluntary force, resting twitch force, voluntary activation, 0-50 ms impulse, 0-100 impulse, 100-200 ms impulse) were measured. RESULTS: Hedonic value (water 47 ± 8%, sweet 23 ± 17%, salt 71 ± 8%, bitter 80 ± 10%), taste intensity, unpleasantness and increases in heart rate (no solution 14 ± 5 bpm, water 18 ± 5 bpm, sweet 20 ± 5 bpm, salt 24 ± 7 bpm, bitter 23 ± 6 bpm) were significantly higher in the salty and bitter conditions compared to control conditions. Nausea was low in all conditions (< 15%) but was significantly higher in salty and bitter conditions compared to water (water 3 ± 5%, sweet 6 ± 13%, salt 7 ± 9%, bitter 14 ± 16%). There was no significant difference between conditions in neuromuscular function or corticomotor excitability variables. CONCLUSION: At rest, unpleasant tastes appear to have no influence on quadricep corticomotor excitability or neuromuscular function. These data question the mechanisms via which unpleasant tastes are proposed to influence exercise performance.