Unpleasant Tastants Do Not Influence Neuromuscular Function Or Corticomotor Excitability Despite Sympathetic Nervous System Activation.

Abstract

Previous research suggests that ingesting a bitter tastant enhances exercise performance. This may be due to activation of the sympathetic nervous system (SNS) in response to the unpleasant taste. However, the mechanisms facilitating changes in performance after ingestion of unpleasant tastants are not yet clear. PURPOSE: To explore the effect of unpleasant tastants on SNS activity, corticomotor excitability, and neuromuscular function. METHODS: Five females and seven males participated in a three-phase experiment. Each phase had two presentations of five conditions in a random order. No solution, water and artificial sweetener were controls for the unpleasant salty (1 M) and bitter (2 mM quinine) solutions. Measurements were taken immediately after each 25 ml solution was mouth rinsed (10 s) and ingested. In Phase 1, hedonic value, nausea, heart rate, and mean arterial pressure were measured to determine perceptual and SNS responses. In Phase 2, quadricep motor evoked potentials (MEPs) were recorded following transcranial magnetic stimulation to assess corticomotor excitability. In Phase 3, quadricep maximal voluntary contractions were performed with electrical femoral nerve stimulation to assess neuromuscular function. One-way repeated measures ANOVAs, with Bonferroni post-hoc comparisons explored differences between conditions. RESULTS: Hedonic value rating was significantly higher (p < 0.05) in the salt (mean ± SD; 75 ± 8) and bitter (76 ± 8) conditions compared to water (47 ± 10) and artificial sweetener (28 ± 18). The increase in heart rate was significantly higher (p < 0.05) in the salt (23 ± 6 bpm) and bitter (21 ± 3 bpm) conditions compared to no solution (13 ± 4 bpm), water (17 ± 4 bpm), and artificial sweetener (18 ± 5 bpm). Change in mean arterial pressure was also significantly higher (p < 0.05) in the bitter (24 ± 5 mmHg) condition compared to no solution (18 ± 3 mmHg), but other conditions were not significantly different. There was no significant difference (p > 0.05) between conditions in nausea, neuromuscular function (max voluntary force, voluntary activation, rate of force development) or corticomotor excitability (MEPs). CONCLUSIONS: Unpleasant tastants influenced markers of SNS activation. However, this did not translate into changes in corticomotor excitability or neuromuscular function.