Mouth exposure to carbohydrate prior to exercise possibly impairs the efficacy of carbohydrate mouth rinsing during exercise

Decker K. P., M. J. Saunders, N. D. Luden, C. J. Womack, and N. J. Hladick. Mouth Exposure to Carbohydrate Prior to Exercise Possibly Impairs the Efficacy of Carbohydrate Mouth Rinsing during Exercise. Purpose: Carbohydrate mouth-rinsing (CHO-MR) during intense endurance exercise has been associated with improved cycling performance, due to neurological influences. However, prior studies have reported the efficacy of CHO-MR is attenuated following a pre-exercise meal. To determine if this outcome is related to desensitization of CHO receptors (rather than metabolic effects following digestion), this study will investigate whether CHO-MR prior to exercise influences cycling performance when CHO-MR is also used during exercise. Methods: Eight trained cyclists (age, 24 ± 6 yr; height, 176 ± 6 cm; weight 75 ± 12 kg; VO2max, 61 ± 8 ml/kg/min) completed three exercise trials, each consisting of 15-min of incremental, constant-load exercise followed by a simulated 30-km time-trial (TT). Treatment beverages in the trials were randomly counterbalanced: a) PL_PL: placebo before and during exercise, b) PL_CHO: placebo pre-exercise, CHO-MR during exercise, and c) R_CHO: CHO-MR before and during exercise. Physiological responses (VO2, VE, RER, RPE, heart rate, blood glucose and lactate) were assessed during constant-load exercise and during the TT. Magnitude-based qualitative inferences were used to evaluate differences in responses between treatments. Results: TT performance was ‘possibly’ impaired (59% likelihood) with R_CHO (57.3 ± 3.6) versus PL_CHO (56.9 ± 3.0 min). Both trials were ‘likely’ slower than PL_PL (55.8 ± 3.1 min), but the reliability of performance data from this trial may have been impacted by measurement error, which limited our ability to determine the influence of CHO-MR during exercise. Physiological responses between treatments during constant-load cycling, and the TT were generally similar between all treatments. Conclusion: A pre-exercise CHO-MR had a possibly negative impact on cycling performance that also included CHO-MR during exercise. Although further evidence is required to validate this finding, our data suggests that desensitization of CHO receptors related to recent CHO exposure may be partially responsible for previous reports that the efficacy of CHO-MR during exercise are attenuated by pre-exercise feedings. Keywords: CYCLING, CARBOHYDRATE, MOUTH-RINSING, PERFORMANCE, ERGOGENIC-AIDS

Gustatory Imagery Reveals Functional Connectivity from the Prefrontal to Insular Cortices Traced with Magnetoencephalography

Our experience and prejudice concerning food play an important role in modulating gustatory information processing; gustatory memory stored in the central nervous system influences gustatory information arising from the peripheral nervous system. We have elucidated the mechanism of the 'top-down" modulation of taste perception in humans using functional magnetic resonance imaging (fMRI) and demonstrated that gustatory imagery is mediated by the prefrontal (PFC) and insular cortices (IC). However, the temporal order of activation of these brain regions during gustatory imagery is still an open issue. To explore the source of "top-down" signals during gustatory imagery tasks, we analyzed the temporal activation patterns of activated regions in the cerebral cortex using another non-invasive brain imaging technique, magnetoencephalography (MEG). Gustatory imagery tasks were presented by words (Letter G-V) or pictures (Picture G-V) of foods/beverages, and participants were requested to recall their taste. In the Letter G-V session, 7/9 (77.8%) participants showed activation in the IC with a latency of 401.7 +/- 34.7 ms (n = 7) from the onset of word exhibition. In 5/7 (71.4%) participants who exhibited IC activation, the PFC was activated prior to the IC at a latency of 315.2 +/- 56.5 ms (n = 5), which was significantly shorter than the latency to the IC activation. In the Picture G-V session, the IC was activated in 6/9 (66.7%) participants, and only 1/9 (11.1%) participants showed activation in the PFC. There was no significant dominance between the right and left IC or PFC during gustatory imagery. These results support those from our previous fMRI study in that the Letter G-V session rather than the Picture G-V session effectively activates the PFC and IC and strengthen the hypothesis that the PFC mediates "top-down" control of retrieving gustatory information from the storage of long-term memories and in turn activates the IC

Mouth Rinsing With Carbohydrate Solutions at the Postprandial State Fail to Improve Performance During Simulated Cycling Time Trials.

Mouth-rinsing with carbohydrate solutions during cycling time trials results in performance enhancements, however the majority of studies have utilised ∼6% carbohydrate solutions. Therefore, the purpose of this study was to compare the effectiveness of mouth-rinsing with 4%, 6%, and 8% carbohydrate (CHO) solutions on 1-h simulated cycling time trial performance. On four occasions, seven trained male cyclists completed at the postprandial period, a set amount of work as fast as possible in a randomised, counterbalanced order. The subjects mouth rinsed for 5-s, upon completion of each 12.5% of the trial, with 25 mL of a non-CHO placebo, 4%, 6%, and 8% CHO solutions. No additional fluids were consumed during the time trial. Heart rate (HR), ratings of perceived exertion (RPE), thirst (TH) and subjective feelings (SF) were recorded after each rinse. Further, blood samples were drawn every 25% of the trial to measure blood glucose (BG) and blood lactate (BG) concentrations, whilst whole body carbohydrate oxidation was monitored continuously. Time to completion was not significant between conditions with the placebo, 4%, 6%, and 8% conditions completing the trials in 62.0 ± 3.0, 62.8 ± 4.0, 63.4 ± 3.4, and 63 ±4.0 minutes respectively. There were no significant differences between conditions in any of the variables mentioned above however significant time effects were observed for HR, RPE, TH, and SF. Post-hoc analysis showed that TH and SF of subjects in the CHO conditions but not in the placebo were significantly increased by completion of the time trial. In conclusion, mouth-rinsing with CHO solutions did not impact 1-h cycling performance in the postprandial period and in the absence of fluid intake. Our findings suggest that there is scope for further research to explore the activation regions of the brain and whether they are receptive to CHO dose, before specific recommendations for athletic populations are established. Consequently mouth-rinsing as a practical strategy for coaches and athletes is questionable under specific conditions and should be carefully considered before its inclusion. The emphasis should be focused on appropriate dietary and fluid strategies during training and competition

Impact of pre-exercise feedings with a low or high glycemic index on the ergogenic effects of carbohydrate mouth-rinsing during cycling

Purpose: Carbohydrate (CHO) ingestion during exercise enhances performance in short endurance events (~ 1 hr) due to neural influences, as demonstrated by the efficacy of CHO mouth-rinsing during cycling. However, the magnitude of these neural effects may be blunted following pre-exercise CHO feedings. This study examined whether the glycemic index (GI) of a pre-exercise meal affected time-trial (TT) performance in cyclists using a CHO mouth-rinse during exercise. Methods: Eight cyclists (age: 24 ± 6 yr; VO2max: 61 ± 8 ml×kg-1×min-1) completed 4 exercise trials, consisting of 15 min of constant-load cycling followed by a simulated 30-km TT. Treatments were: a) L-CHO: low GI CHO beverage pre-exercise (1.5 g×kg-1 CHO, 120 min prior), CHO mouth rinsing during exercise (6.4% maltodextrin solution), b) H-CHO: high GI CHO beverage (1.5 g×kg-1 CHO) pre-exercise, CHO mouth rinsing during-exercise, c) PL-CHO: placebo beverage pre-exercise, CHO mouth rinsing during exercise, and d) PL-PL: placebo beverage pre-exercise, placebo mouth rinsing during exercise. Blood glucose was measured before beverage consumption and at 30 and 120 min following ingestion. Physiological measurements (VO2, VE, RER, HR, RPE, glucose, lactate, and gastrointestinal distress) were assessed during constant-load cycling and the TT. Magnitude-based qualitative inferences were used to assess differences in responses between trials. Results: Blood glucose differed among treatments 30 min post-feeding (H-CHO \u3e L-CHO \u3e PL-CHO = PL-PL), and was lower in H-CHO versus PL-CHO and PL-PL during subsequent exercise. Compared to PL-CHO, TT performance was faster in both L-CHO (-0.5 ± 0.8 min; “likely” beneficial) and H-CHO (-0.7 ± 0.7 min; “likely” beneficial), with no systematic differences between L-CHO and H-CHO. However, none of the 3 mouth rinse trials were clearly different from the PL-PL trial. Conclusions: When using a CHO mouth rinse during exercise, CHO ingestion 2 hr prior to cycling enhanced TT performance versus exercise in the fasted state. The GI of the pre-exercise feeding did not systematically affect TT performance in cyclists using a CHO mouth-rinse. However, the impact of these findings is confounded by the lack of performance differences versus a control trial without CHO before or during exercise

Cognitive Keys in Psychophysical Estimation of Chemosensory Perception in University Students

Psychophysical methods allow us to measure the relationship between stimuli and sensory perception. Of these, Detection Threshold (DT) allows us to know the minimum concentration to produce taste identification. Given this, we wonder whether, for example, wine tasting experts are more capable of perceiving their sensory properties than other people, or whether they can distinguish them because they are better able to “describe” them. To verify this, this study analyses the influence of having prior knowledge of the name astringency and, failing that, to detect it and distinguish it between the four basic tastes. One-hundred-and-sixty-two university students with an average age of 19.43 (SD = 2.55) years were assigned to three experimental conditions: an experimental group (G.2) without previous knowledge of the name astringency and with alimentary satiety, and two control groups, both with previous knowledge of the name, these being G.1, with satiety, and G.3, with hunger. DT was collected for the four basic tastes and astringencies. Results showed significant differences in the identification of astringency, being the least identified experimental group with respect to the control groups. It is striking that G.2, without prior knowledge of the name, identified astringency as a bitter taste in most cases. This supports our hypothesis of the importance of attending to linguistic cognitive processes when psychophysically estimating taste in human

The effect of carbohydrate mouth rinsing on fencing performance and cognitive function following fatigue-inducing fencing

This study investigated the impact that mouth rinsing carbohydrate solution has on skill-specific performance and reaction time following a fatigue inducing bout of fencing in epee fencers. Nine healthy, national level epee fencers visited a laboratory on 2 occasions, separated by a minimum of 5 days, to complete a 1-minute lunge test and Stroop test pre and post fatigue. Heart rate and ratings of perceived exertion (RPE) were recorded during completion of the fatiguing protocol. Between fights the participants mouth rinsed for 10 seconds, either 25ml of 6.7% maltodextrin solution (MALT) or water (PLAC). Blood lactate and glucose were recorded at baseline, pre- and post-testing. Results showed an increase in heart rate and overall RPE over time in both conditions. There were no differences in blood glucose (F(1,8)=.63, P=.4, ηp=.07) or blood lactate levels (F(1,8)=.12, P=.70, ηp=.01) between conditions as a function of time. There was a significant improvement in lunge test accuracy during the MALT trial (F(1,8)=5.21, P=.05, ηp=.40) with an increase from pre (81.2 ±8.3%) to post (87.6 ±9.4%), whereas there was no significant change during the placebo (pre 82.1 ±8.8%, post 78.8 ±6.4%). There were no recorded differences between conditions in response time to congruent (F(1,8)=.33, P=.58, ηp=.04) or incongruent stimuli (F(1,8)=.19, P=.68, ηp=.02). The study indicates that when fatigued mouth rinsing MALT significantly improves accuracy of skill-specific fencing performance but no corresponding influence on reaction time was observed

Brain activity and connectivity changes in response to glucose ingestion

Objectives: The regulatory role of the brain in directing eating behavior becomes increasingly recognized. Although many areas in the brain have been found to respond to food cues, very little data is available after actual caloric intake. The aim of this study was to determine normal whole brain functional responses to ingestion of glucose after an overnight fast.Methods: Twenty-five normal weight, adult males underwent functional MRI on two separate visits. In a single-blind randomized study setup, participants received either glucose solution (50 g/300 ml of water) or plain water. We studied changes in Blood Oxygen Level Dependent (BOLD) signal, voxel-based connectivity by Eigenvector Centrality Mapping, and functional network connectivity.Results: Ingestion of glucose led to increased centrality in the thalamus and to decreases in BOLD signal in various brain areas. Decreases in connectivity in the sensory-motor and dorsal visual stream networks were found. Ingestion of water resulted in increased centrality across the brain, and increases in connectivity in the medial and lateral visual cortex network. Increased BOLD intensity was found in the intracalcarine and cingulate cortex.Discussion: Our data show that ingestion of glucose leads to decreased activity and connectivity in brain areas and networks linked to energy seeking and satiation. In contrast, drinking plain water leads to increased connectivity probably associated with continued food seeking and unfulfilled reward.Trail registration: This study combines data of two studies registered at clinicaltrails.gov under numbers NCT03202342 and NCT03247114.Multivariate analysis of psychological dat

Comparing Taste Perception Across Modalities in Healthy Adults: Liquids Versus Dissolvable Taste Strips

Taste stimulation has rehabilitative value in dysphagia management, as it activates salient underlying afferent pathways to swallowing which may evoke feedforward effects on swallow biomechanics. Despite its potential beneficial effects on swallow physiology, taste stimulation’s clinical application is limited for persons unsafe to orally consume food/liquid. This study aimed to create edible, dissolvable taste strips matched to flavor profiles previously used in research assessing taste’s effects on swallowing physiology and brain activity, and to evaluate how similar their perceived intensity and hedonic, or palatability, ratings were between their liquid counterparts. Plain, sour, sweet–sour, lemon, and orange flavor profiles were custom-made in taste strips and liquid modalities. The generalized Labeled Magnitude Scale and hedonic generalized Labeled Magnitude Scale were used to assess intensity and palatability ratings for flavor profiles in each modality. Healthy participants were recruited and stratified across age and sex. Liquids were rated as more intense than taste strips; however, there was no difference in palatability ratings between the modalities. There were significant differences across flavor profiles in intensity and palatability ratings. Collapsed across liquid and taste strip modalities, pairwise comparisons revealed all flavored stimuli were rated as more intense than the plain profile, sour was perceived as more intense and less palatable than all other profiles, and orange was rated as more palatable than sour, lemon, and plain tastants. Taste strips have useful implications for dysphagia management, as they could offer safe and patient-preferred flavor profiles to potentially provide advantageous swallowing and neural hemodynamic responses