SUMMARY: High carbohydrate drinks improve short term performance (<1 hour) when swished in the mouth without swallowing (Burke & Maughan, 2015). Swallowing may increase performance benefits, but at the risk of discomfort during performance (i.e. nausea, bloating).
Current research suggests high carbohydrate drinks improve performance through altering the perception of fatigue rather than by refueling energy stores (Burke & Maughan, 2015). The following has been largely adapted from review of the literature performed by Burke and Maughan (2015).
Carbohydrates do not refuel muscles quickly enough to account for changes in performance.
The use of a sugary drink such as Coca-Cola or Gatorade to speed recovery is commonplace in many sports. It has been thought that ingesting these drinks may refuel energy reserves allowing athletes to continue in the face of exhaustion (Burke & Maughan, 2015).
The benefit of such drinks in this regard is well documented; it is clear the ingestion of carbohydrates in the form of sugar can improve performance in the short term. However, it is not clear how this occurs (Burke & Maughan, 2015). While carbohydrate ingestion over longer periods does result in refueled muscle glycogen (an important indicator of muscle-energy reserves), the speed at which carbohydrates are absorbed and transported to the working muscle is too slow to account for changes in performance if the drink is ingested during exercise. (Burke, Wood, Pyne, Telford, & Saunders, 2005). Instead of acting in this metabolic manner, current research is suggesting a neural mechanism.
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Sugar Affects the Brain!
It is proposed that receptors in the mouth and along the gastrointestinal tract bind sugars and other molecules as they are ingested and influence the brain’s reward and motor systems (Burke & Maughan, 2015).
What does the brain have to do with fatigue? The answer: everything. While levels of carbohydrates, heart rate, and core temperature (among many other physiological markers) can influence the perception of fatigue, it is ultimately the experience of fatigue that causes us to discontinue exercise.
This experience is thought to be an evolutionary adaption that prevents us from pushing ourselves to dangerous internal conditions (Burke & Maughan, 2015). Therefore, there is the potential to “trick” ourselves to push on. This is the general idea as to why swishing a carbohydrate drink in your mouth can improve your performance.
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Support for this theory has come in many forms:
- Neurotransmitter (signaling molecules in the brain) modifying drugs have been shown to reduce aerobic performance (Wilson & Maughan, 1992). This demonstrates the brain can alter maximal exertion.
- Carbohydrate solutions taken orally have been shown to offer performance improvement where solutions given intravenously have not (Jeukendrup, Brouns, Wagenmakers, & Saris, 1997; Carter, Jeukendrup, Mann, & Jones, 2004). This suggests the GI tract must be in some way related to the improvement in performance.
- Carbohydrate drinks given to exercisers with adequate energy reserves still show improvements in performance (Jeukendrup, Brouns, Wagenmakers, & Saris, 1997; Carter, Jeukendrup, & Jones, 2004a; Carter, Jeukendrup, Mann, & Jones, 2004b). It is therefore unlikely benefits are derived from refueling working muscles.
- Carbohydrates, when in the mouth, have been shown to alter brain activity in a manner that has previously been associated with changes in exercise performance (Wilson & Maughan, 1992; Chambers, Bridge, & Jones, 2009; Burke & Maughan, 2015).
- Numerous studies have demonstrated improved performance when subjects drink, swirl, and then spit out sugary drinks. (Chambers, Bridge, & Jones, 2009; Pottier, Bouckaert, Gilis, Roels, & Derave, 2010; Lane, Bird, Burke, & Hawley, 2012; Sinclair, et al., 2014).
Based on these findings, it is worth trying a flat soda the next time you are on a long bike ride to see for yourself! It is worthwhile to note that although the effect of swirling a carbohydrate drink in your mouth is highest after dietary fasting, the best performance is achieved through both eating beforehand and then ingesting a sugary drink (Burke & Maughan, 2015).
Should it be a hot day, drinking the beverage cold offers even more improvement. While swallowing the drink has shown the greatest increases in performance, drinking large volumes may cause bloating or nausea. Swirling in the mouth and spitting is recommended for individuals concerned with discomfort (Burke & Maughan, 2015).
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Burke, L. M., Wood, C., Pyne, D. B., Telford, R. D., & Saunders, P. U. (2005). Effect of carbohydrate intake on half-marathon performance of well-trained runners. International journal of sport nutrition and exercise metabolism, 15(6), 573-589. Retrieved from https://www.researchgate.net/profile/Louise_Burke2/publication/7256034_Effect_of_Carbohydrate_Intake_on_Half-Marathon_Performance_of_Well-Trained_Runners/links/09e4150daece98786b000000/Effect-of-Carbohydrate-Intake-on-Half-M.
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