It could be said that carbohydrates are an endurance athlete’s best friend. Without them we would fatigue and be unable to sustain the 20,000 or so muscle contractions it takes to complete a 4 hour ride. Physiologically speaking carbohydrates (CHO) are the main fuel source (combined with fat) to supply energy to not only skeletal muscle but also the brain, nervous system and cardiac muscle. Although we usually consume CHO to support muscle contraction and maintain blood glucose there are a few intriguing roles of CHO that many athletes are not aware of.
Generally speaking the rate limiting step in getting CHO to the muscle is the absorption from the gut into the blood stream. Carbohydrates come in various forms. This includes small and simple CHO such as glucose, fructose and galactose which are all monosaccharide’s. Bigger more complex CHO take longer to absorb as they are by nature more complex and take longer to breakdown before being absorbed. Under laboratory conditions we know that during intense exercise skeletal muscle can oxidise glucose at a rate much greater than we can absorb it and until recently the maximal rate of exogenous (consumed) CHO oxidation was thought to be ~1g/min.
In a study that has now seen the development of a well known brands ‘C2max’ energy gel formula researchers experimented with using multiple carbohydrate mixtures to see if they could increase the absorption rate when compared to glucose alone. Interestingly when they combined glucose with fructose they found that absorption could be increased by ~50% which then resulted in a significantly greater rate of exogenous CHO oxidation at the muscle (~1.7g/min). This finding was attributed to the possibility that glucose and fructose have different transporters across the gut wall and they coined the term ‘multiple CHO transporters’, which has had much interest over the last few years. For a more in depth insight into all this check out http://www.ncbi.nlm.nih.gov/pubmed/20574242
These same researchers have discovered an even more interesting fact about CHO that could have significant performance benefits for a range of athletes. As already discussed CHO is the primary fuel source for muscle contraction during high intensity exercise however, it appears that CHO may also play a role via centrally mediated mechanisms. By ‘centrally mediated’ I refer to the complex role of the brain and its neural control over skeletal muscle. In a study that looked at the effects of intravenously infusing glucose versus the traditional oral ingestion of glucose on cycling time trial performance an unexpected finding was revealed. These researchers observed that the distance covered during a 1-hour time trial was significantly greater under the conditions where subjects ingested the glucose orally. They developed the hypothesis that there may be receptors in the mouth that can sense CHO and can positively affect the brain in a way that enhances performance.
Since this first study there have been a multitude of studies completed to further investigate this remarkable role of orally ingesting CHO. It has even been shown that mouth rinsing a CHO solution then spitting it out (without swallowing any) enhances performance. These studies have confirmed that; 1) Certain areas of the brain related to motivation respond to CHO in the mouth, 2) It is the calorific (energy containing) characteristic of CHO that trigger these receptors because an artificially sweetened solution does not have the same effect and 3) It appears that the duration the solution is rinsed in the mouth is important.
Although much light has been shed on this topic there are still a few small things we are trying to figure out. It is not yet clear if this mouth rinse procedure still has an effect after a meal high in CHO has been consumed. Because most research studies require subjects to come into the laboratory without eating breakfast (fasted) we are not sure if under real life circumstance where an athlete would eat breakfast before an event if the rinse procedure is still effective. This question is currently being followed up by RMIT researchers in collaboration with the Australian Institute of Sport in hope that they can provide a clear set of guidelines for athletes competing in the 2012 London Olympics.
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