The bitter taste of victory: effects of a bitter tasting quinine solution on maximal intensity exercise performance

Sharon Gam

    Research output: ThesisDoctoral Thesis

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    Abstract

    [Truncated] It is generally acknowledged that for an ergogenic aid administered orally to enhance exercise performance it must first be absorbed by the gastrointestinal (GI) tract before exerting its effects. Recently, however, it has been reported that some ergogenic aids can affect exercise performance without their prior absorption by the GI tract. This is best illustrated by the many studies which, over the past decade, have shown that rinsing the mouth with a carbohydrate (CHO) solution, without swallowing it, significantly improves the performance of endurance exercise, short sprints, and maximal voluntary force production. These ergogenic effects of CHO mouth rinsing have been attributed to the activation of the brain by afferent taste signals, but the specific mechanisms by which this brain activation translates to enhanced exercise performance has not yet been elucidated. Given the benefits of CHO mouth-rinsing on exercise performance, this raises the issue of whether other types of tastants, such as bitter tasting solutions, may also improve exercise performance. For this reason, the purpose of this thesis was to investigate whether the bitter tasting quinine can improve maximal sprint performance, and, if so, to examine some of the possible mechanisms whereby this effect may occur.

    The first study of this thesis investigated whether mouth rinsing combined with the ingestion of a bitter tasting quinine solution improves the performance of maximal cycling sprint in male competitive cyclists. A combined mouth rinse and ingestion protocol was implemented in this study in order to activate as many bitter taste receptors (T2Rs) in the oral cavity and remainder of the upper GI tract as possible. Since the effect of quinine on performance had never been investigated previously, this study was conducted in two parts. The first part of the study determined the dose response relationship between quinine concentration and both subjective taste responses and objective autonomic nervous system (ANS) responses. A 2 mM quinine solution was chosen since mouth rinsing and ingesting quinine at this concentration significantly activated measures of ANS function such as skin conductance amplitude, ohmic perturbation duration, and instantaneous heart rate amplitude without causing significant feelings of nausea. In order to investigate the effect of quinine on sprint performance, a group of trained competitive cyclists were asked to rinse their mouth for 10-s and then ingest either the bitter tasting 2 mM quinine solution, a sweet tasting aspartame solution, plain water, or no rinse at all (control), with each treatment administered on separate days following a counterbalanced study design. Immediately after ingesting the solution, participants performed a maximal 30-s sprint on a cycle ergometer. Mean power output during the sprint was significantly higher after quinine administration compared with the other three conditions, and peak power output was higher compared with the water and control conditions. There were no differences in heart rate, rating of perceived exertion or blood variables (i.e. blood lactate and glucose) between the four conditions. Since the sprint was performed immediately after the ingestion of the quinine solution (therefore not allowing time for the quinine to be absorbed by the gastrointestinal tract), it is likely that the ergogenic effect of the combination of mouth rinsing and ingestion of quinine on maximal sprint performance was mediated by taste signals originating from T2Rs in the oral cavity and upper esophagus, which in turn may have activated the areas of the brain associated with emotional processing and motor behaviour.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2014

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