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.
If you are interested in being a subject for this study you
can contact stephen.lane@rmit.edu.au
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