One my of exercise physiology mentors at the University of Southern California used to exercise during his lunch break. I’ll never forget him making his pre-exercise fuel prior to his workout. I know what you’re thinking: this over-educated science lab rat probably takes more supplements than I’ve heard of!
His drink consisted of: water and Pixy Stix.
That’s it. He proclaimed this sugar water was the same as Gatorade.
I always got a kick out of his antics, but he made a great point and this isn’t a knock at Gatorade as it is well established that drinking a carbohydrate (CHO) packed drink prior to exercise is beneficial. These pre-exercise drinks are sold by many leading drink manufacturer and typically contain high volumes of sugar and maltodextrin to provide a short blood glucose increase and energy.
Despite the noted improvements, no physiological reasoning has been established for consuming a carbohydrate product during exercise. The improvements with carbohydrate products during exercise is unclear because it seems that blood glucose concentrations are well maintained and may even increase because of the increased output of hepatic glucose.
Moreover, consuming carbohydrates has been reported to make a minimal contribution to carbohydrate oxidation in the muscle in comparison with the oxidation of endogenous muscle glycogen during a short-duration exercise. Furthermore, the concentrations of muscle glycogen are unlikely to be limiting during endurance performance approximately 1 h in duration (Rollo 2010).
However, during consumption sensory receptors in the mouth and pharynx are activated prior to consumption. These sensory inputs affect voluntary motor behavior, in addition to sub serving perception and initiating early digestive reflexes (Zafra et al., 2006).
These lead researchers to look at only rinsing the mouth with a carbohydrate drink.
Remarkably, the mere presence of carbohydrate in the mouth has been shown to improve performance during prolonged physical activity (Carter et al., 2004; Chambers et al., 2009; Rollo et al., 2008). Don’t believe me; let’s take a look at the research!
- Rollo 2010 et al. found that ingesting a carbohydrate–electrolyte solution significantly improved 1-h running performance in comparison with mouth rinsing the same carbohydrate–electrolyte solution or ingesting the same volume of a placebo solution. The results of this study confirm previous observations that the ingestion of a 6.4% carbohydrate–electrolyte solution improved 1-h running performance in fasted runners.
- Pottier et al. reported that mouth rinsing a 6% carbohydrate–electrolyte solution (sucrose = 5.4 g/100 mL, glucose = 0.46 g/100 mL improved cycling performance by 3.7% compared with ingesting the same solution mL/kg body mass (BM). The authors suggested that improved performance was due to CHO in the mouth acting on a centrally governed mechanism. However, these results are perplexing, given that the mouth was exposed to the same CHO solution in both the ingestion and rinse trials. The authors speculated that the ergogenic effect of having CHO in the mouth may be lost when ingesting a carbohydrate–electrolyte solution due to the short oral transit time.
- Gant 2010 found an immediate improvement in carbohydrate consumption and said this immediate ergogenic effect precedes substrate or endocrine signaling from the viscera. The mechanism is most likely neural, and represents a novel form of sensorimotor integration.
I’m going to let Rollo 2011 take it from here:
“The link between CHO ingestion and the CNS, specifically the brain, has been studied using functional magnetic resonance imaging (fMRI). In a recent study, fMRI was used to examine the influence of oral exposure of glucose and maltodextrin on the brain. Chambers et al. reported that both glucose and maltodextrin in the mouth activate regions in the brain associated with reward, such as the insula/frontal operculum, orbitofrontalcortex, and striatum.
Speculatively, this ‘‘central effect’’ may explain reports from studies that have found that simply having CHO in the mouth has a positive effect on cycling time trial performance. Furthermore, these studies suggest that some of the benefits associated with CHO ingestion during endurance performance may be due to the feed-forward mechanisms originating from the mouth. It is important to note, however, that not all studies have reported that CHO ingestion benefits time trial performance.
The mechanism responsible for improved performance in the carbohydrate–electrolyte trial is unlikely to be a consequence of the increased rate of exogenous CHO oxidation or elevated respiratory exchange rate (RER). Instead, reports from previous studies suggest that the increased rate of CHO oxidation is a consequence of the elevated running speed, i.e., exercise intensity during the CHO trial. The absence of a clear metabolic advantage of providing additional substrate during laboratory time trials has led authors to speculate that CHO ingestion may have a positive effect on the central nervous system (CNS).
Several studies have used fMRI to investigate the central response to ingesting CHO solutions. Smeets et al. reported that the ingestion of a glucose solution resulted in the activation of the hypothalamus, which was not observed with the ingestion of water, aspartame, or maltodextrin solution. The time course of activation corresponded with changes in blood glucose and insulin concentrations after CHO ingestion. Interestingly, the onset of activation began before the end of glucose ingestion, i.e., before the glucose entered the bloodstream. This phenomenon was investigated in detail by Chambers et al., who reported that simply mouth rinsing both glucose and maltodextrin activated regions in the brain associated with reward. In addition, a recent study also provides evidence that CHO in the mouth can increase the excitability of the corticomotor pathways. Therefore, a ‘‘central effect’’ provides an appealing hypothesis to explain improved endurance performance when ingesting CHO–electrolyte solutions without any apparent peripheral metabolic changes. However, the results of the present study suggest that it is too early to recommend athletes mouth rinse and expectorate carbohydrate–electrolyte solutions as the performance benefit was only observed after mouth rinsing and ingestion (Rollo 2011)”.
“The presence of carbohydrate in the mouth facilitated corticomotor excitability, even when it was simply held in the mouth and not swallowed. This was most likely due to activation of receptors in the mouth producing afferent activity in the facial, glossopharyngeal and vagus nerves. These afferent pathways project to the solitary nucleus in the medulla and pons (Bailey et al., 2006), where they may have the opportunity to influence descending motor activity (Yatesand Stocker, 1998), particularly the polysynaptic reticulospinal tract that modulates the gain of spinal motor neuron pools (Gant 2010)”.
The results are not crystal clear, but it does appear only swishing a carbohydrate drink in your mouth prior to endurance exercise improves performance. More research is needed, but this uncommon practice is one area research may be ahead of the athletes.
Despite popular anecdotal use, we must remember, we don’t have all the answers! This isn’t suggesting we will find all the answers in research, but top athletes aren’t always ahead of the curve. Use this knowledge and expand your understanding to advance the sport.
- Beelen M, Berghuis J, Bonaparte B, Ballak S, Jeukendrup AE,van Loon LJC. Carbohydrate mouth rinsing in the fed state does not enhance time trial performance. Int J Sport Nutr Exerc Metab.2009;19:400–9.
- Carter JM, Jeukendrup AE, Jones DA. The effect of carbohydratemouth rinse on 1-h cycle time trial performance. Med Sci SportsExerc. 2004;36(12):2107–11.
- Chambers ES, Bridge MW, Jones DA. Carbohydrate sensing in thehuman mouth: effects on exercise performance and brain activity.J Physiol. 2009;578(Pt 8):1779–94. Gant N, Stinear CM, Byblow WD. Carbohydrate in the mouthimmediately facilitates motor output. Brain Res. 2010;1350:151–8.
- Liu Y, Gao JH, Liu HL, Fox PT. The temporal response of thebrain after eating revealed by functional MRI. Nature. 2000;405:1058–62.
- Smeets PA, de Graaf C, Stafleu A, van Osch MJ, van der Grond J.Functional MRI of human hypothalamic responses following glu-cose ingestion. Neuroimage. 2005;24:363–8.37.
- Svebak S, Murgatroyd S. Metamotivational dominance: a multi-method validation of reversal theory constructs. J Pers Soc Psychol.1985;48:107–16.
- Pottier A, Bouckaert J, Gilis W, Roels T, Derave W. Mouth rinsebut not ingestion of a carbohydrate solution improves 1-h cycletime trial performance. Scand J Med Sci Sports. 2008;20:105–11.29.
- Rollo I, Cole M, Miller R, Williams C. The influence of mouth-rinsing a carbohydrate solution on 1-h running performance. MedSci Sports Exerc. 2010;42(4):798–804.30.
- Rollo I, Williams C. Influence of ingesting a carbohydrate–electrolyte solution before and during a 1-hr running performancetest.Int J Sport Nutr Exerc Metab. 2009;19:645–58.31.
- Rollo I, Williams C. Influence of ingesting a carbohydrate–electrolyte solution before and during a 1-hour run in fed endurance-trained runners. JSports Sci. 2010;28:593–602.32.
- Rollo I, Williams C, Gant N, Nute M. The influence of carbohy-drate mouth rinse on self-selected speeds during a 30-min treadmillrun.Int J Sport Nutr Exerc Metab. 2008;18:585–600.33.
- Rollo I, Williams C, Nevill A. Repeatability of scores on a noveltest of endurance running performance. J Sports Sci. 2008;26:1–8.
- Rollo I, Williams C, Nevill M. Med Sci Sports Exerc. Influence of ingesting versus mouth rinsing a carbohydrate solution during a 1-h run. 2011 Mar;43(3):468-75.
- Zafra MA, Molina F, Puerto A. The neural/cephalic phase reflexes in the physiology of nutrition. Neurosci Biobehav Rev. 2006;30(7):1032-44. Epub 2006 May 5. Review.
By G. John Mullen founder of the Center of Optimal Restoration, head strength coach at Santa Clara Swim Club, creator of the Swimmer's Shoulder System, and chief editor of the Swimming Science Research Review.