Which form of carbohydrate is most effect at improving the endurance
performance of runners and cyclists?
A position paper for cyclists and runners
Joe Klapper
Fall 2005
Carbohydrate food intake is the most common way to reduce glycogen loss to
help prevent muscle fatigue and shutdown. However, there are two main forms of
carbohydrates (food and liquid), and which one works better at preventing fatigue and
improving endurance times? There are many articles that have differing data on whether
solid or liquid forms of carbohydrates (CHO) work better to lengthen the endurance times
of endurance athletes including runners and cyclists. If muscle fatigue can be prevented,
endurance athletes can run or bike for longer periods of time.
Common solid carbohydrates include bread, cereal, pasta, cookies and others.
The most popular forms of liquid carbohydrates are the popular sports drinks being sold
today. Both forms are said to be beneficial to runners and cyclists in order to improve
their performance levels. However, which form helps endurance more? For runners and
cyclists, every second matters. Every day their diet consists of foods and drinks that will
help improve their endurance and reduce their fatigue. It is very important for them to
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know what the food they eat does to their body and how it will affect their performance
level. Liquid sports drinks are well known to help replenish the body during and after
exercise. However, what does this carbohydrate-filled drink actually do to help improve
physical performance? Is it better to drink a sports drink prior and during exercise rather
than eating a CHO rich meal or candy bar before exercise? It would be greatly valuable
for runners and cyclists to know this information because of how important every second
is to them. If the carbohydrates in those sports drinks can improve their endurance more
than the carbohydrates that are received from meal sources, then it is quite possible they
will begin drinking liquid CHO drinks more often prior to exercise rather than eat a
carbohydrate meal.
Articles were found showing that liquid forms of CHO improved the performance
levels of endurance athletes. Similarly, articles were also found that showed solid forms
of CHO improving the performance levels of cyclists and runners. A few articles went
one step further and compared both forms of carbohydrates in their specific study. A
study performed by Neufer et al (1987) compared the effectiveness of liquid CHO and
solid CHO on improving the physical performance of endurance athletes. The results
show a significant difference in the amount of work output that was possible. As figure
1 shows, the work output in N*m that was possible when fed CHO in meal form was
128,118 N*m, compared to 114,442 when fed liquid carbohydrate drinks. Another study
performed by Peters et al (1995), also compared liquid and solid CHO ingestion with
regards to improving physical performance. However, different from the Neufer study,
this study found that the maximum running time for subjects given liquid forms of CHO
was much longer compared to semi-solid forms of carbohydrates (banana with
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marmalade, water and bread mixed together). Figure 2 shows the results from this study.
Because of these two studies, it is clear there is conflicting data in the scientific
community with regards to which form of carbohydrate is better for improving the
physical performance of endurance athletes such as runners and cyclists.
The results observed after comparing all the articles were very diverse. As stated
above some articles claimed liquid CHO did help to improve physical performance and
some articles said solid forms of CHO improved performance. There were also articles
that found the opposite of the previous two sentences, liquid CHO did not help or solid
CHO did not help to improve performance. As a whole, majority of the articles focused
on liquid CHO. This does not, however, mean that liquid CHO is more effective at
improving physical performance levels in endurance athletes; it simply means liquid
CHO has been studied more.
The articles in this argument are research reports that covered carbohydrate intake
and how they affect the performance of athletes. All the articles are from within the last
20 years with the majority of them being in the last ten. Every article’s research question
was whether or not carbohydrate intake prior and or during exercise can improve the
physical performance of endurance athletes such as runners and cyclists. Most of the
articles controlled what the subjects ate prior to the experiment. It is important to control
the intake of other nutrients to observe how carbohydrates (CHO) can improve
performance. Each article kept the subjects’ VO2 max at a constant. The VO2 max is
the maximum amount of oxygen that can be removed from circulating blood and used by
the working tissues during a specified period. This was done in order to see what the
maximum test time or maximum endurance times could be at a certain running or biking
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level. All of the articles did a good job at picking subjects that were in good physical
health. They also tried to pick subjects that were well trained athletes for either running
or cycling. The consistency of subject characteristics is important in order to have
endurance times comparing similar subjects. This allows the experimenter to make the
best judgment as to which form of carbohydrate is the best at maximizing endurance
times.
The position that I am going to argue for is that carbohydrates in solid form
(pasta, cereal, candy bars, etc.) are more effective at helping to improve endurance times
in runners and cyclists than liquid CHO. The main counterargument for this issue is that
carbohydrates in liquid form (sports drinks) are more effective than solid CHO at
improving endurance times and physical performance levels for runners and cyclists.
The reasons the position chosen is the best one are the studies have a stronger
methodology, the variety of solid CHO observed, and it makes the most sense
mechanistically.
The methodology of the solid CHO pile of evidence is superior to liquid CHO
because the experimenters kept the subjects in the laboratory and controlled the diet the
subjects received in the days prior to the experiment. A study performed by Kirwan et al
(1998) observed the effects of different types of cereal and how they can enhance
performance. Subjects were required to “live in the General Clinical Research Center for
2 consecutive days and 3 nights before each trial,” in order to “control physical activity
and dietary intake.” The subjects were told what to eat during the days leading up to
experiment in order to control the other nutrients within the body. This allowed the
researchers to observe the differences that the CHO in the cereal can have on exercise
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performance. As shown in figure 3, the subjects had an endurance time of 266 minutes
when they ate the cereal, and 225 minutes when given a placebo. This shows a drastic
difference in times, and that can be associated with staying in the laboratory for a set
amount of time. Their performance is maximized and it is easier to tell how the solid
CHO worked to improve endurance. Similar to Kirwan, the study by Neufer et al (1987)
followed a procedure like the one that was performed by Kirwan. The subjects were
required to come in a day prior to the study in order to control how they exercised and
what they ate. As observed previously, the solid CHO had a higher work output
compared to liquid CHO. Having the subjects stay at the laboratory longer enables the
experimenter to perform the necessary tests and limit the amount of factors that could
hinder results from being maximized.
One of the factors that could inhibit endurance time is the diet that was consumed.
Having a diet that is rich in CHO and has the other nutrients at a constant level would be
the ideal situation to have in order to maximize the endurance times when given CHO.
Lamb et al (1991) instructed the participants to either be on a 90% CHO diet or a 50%
CHO diet with other nutrients covered in the remaining percentages. Within those two
percentage groups, the subjects were also instructed to either be given pasta or a CHO
supplement the day before the study. While there is no difference in the results of the
two groups when under a 90% CHO diet, the run time to fatigue was higher for the pasta
group in a 50% CHO diet compared to that of the supplement group with a 50% CHO
diet. This is shown by the graph in figure 4.
The counterargument articles did not give out mandatory orders regarding what
foods to eat, however the just gave suggestions on what the subjects should eat. There
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was no supervision given by the experimenters to ensure the subjects ate the food
suggested to them. The subjects could have eaten any food they wanted to, and not
followed the guidelines suggested by the experimenters. Anastasiou et al (2004) did what
was previously stated. They just instructed the subjects on what they could and could not
eat or how they could exercise prior to the experiment. The subjects also were not
required to stay at the laboratory. It is not as effective as having the subjects stay in the
laboratory and have a controlled diet given to them. How do the experimenters know the
subjects did not ingest salty foods that have no CHO? It is easier to control the non
important variables when in the presence of the subjects. By controlling other variables
such as other nutrients, it is easier to observe how different forms of carbohydrates can
affect the exercise performance of endurance athletes.
The only counterargument article that did give the subjects a set diet was
performed by Desbrow et al (2004). They did not make the subjects stay in the
laboratory, but they did make suggestions on foods they should eat. The experimenters
gave the subjects foods that were suggested and wanted them to eat these prior to the
experiment. The subjects were also “provided with a race breakfast for the morning of
the trial.” While the methods regarding foods were strong in this article, they did not
make the subjects stay at the laboratory. They relied on the subjects’ honesty that they
would ingest the given foods.
Another reason the position taken is the strongest is because many different types
of solid carbohydrates were tested. This is a good way to see how it is not just one type
of CHO that can improve physical performance. As read above, pasta was used, and so
were cereal forms of carbohydrates. Carbohydrates can also take the form of bananas as
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shown in the study by Murdoch et al (1993). This study examined whether solid or
slurried forms of bananas were more effective at improving the endurance performance to
exhaustion. The endurance times that were observed were 28.2, 44.1, and 46.4 minutes
for placebo, slurried, and solid ingestions, respectively. While the slurried banana is
taken at the same time as water in this experiment, it is still somewhat solid form.
Overall, this paragraph shows how many different types of CHO can be taken in order to
lengthen endurance times in runners and cyclists.
The counterarguments only focused on liquid sports drinks. While there are many
types of liquid sports drinks (many different brands), all of these drinks are similar in
content. The only problem with this is there was no other method that was tested.
Protein shakes were not tested with regards to the CHO content within them affecting
endurance times in runners or cyclists. The shakes were only studied for body builders,
who use completely different muscles than endurance athletes like runners and cyclists.
Soda was not tested to see if it will enhance endurance. Majority of the articles
suggesting that liquid CHO is the superior are articles that tested sports drinks. Had soda
or any other form of liquid with CHO in it been tested on runners and cyclists to observe
endurance times, there would be a big difference in results because of the amount of other
nutrients which hinder the paths of the CHO from directly affecting the muscles. There
would be more negative results rather than positive. In contrast, many different CHO
foods have the same effect on endurance times.
The unique method of the counterargument articles is that the liquid CHO can be
given at increments during the study. Khanna et al (2005) observed whether a CHOelectrolyte drink supplied during exercise can improve endurance performance. The
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carbohydrate drink was supplied every 15 minutes until exhaustion. The endurance time,
compared with the placebo, was significantly better when given the CHO drink (94.1 min
compared to 62.3). Giving the liquid CHO in increments is supposed to provide muscles
with the desired glycogen needed to prevent muscle fatigue over a longer period of time.
The liquid CHO travels fast through the body and works quicker than the solid CHO
since the solid CHO is given well prior to exercise and gradually helps the muscles
fatigue level. This is one good example of how giving CHO in increments during
exercise works to improve the performance of endurance athletes. .
The position articles do not address giving the solid CHO in intervals because
each is in meal form. It would be really hard to give a subject more solid CHO during
exercise. Solid CHO works gradually, not rapidly. It is not effective to take solid CHO
during a race because it will take that much longer for the food to work to reduce muscle
fatigue. It sits in the stomach until it dissolves into smaller molecules that travel through
the blood system.
In contrast to the statement that giving liquid CHO in increments during exercise
lengthens endurance times, Jarvis et al (1999) found that the increments did not help to
improve the endurance times in cyclists. Jarvis not only found that increments did not
work, but liquid CHO did not work at all to improve endurance times. The subjects were
either given the CHO drink or a placebo at intervals of 10 minutes for 50 minutes. The
rate of fatigue was almost identical for both groups (26% for the placebo and 27.2% for
CHO) suggesting that neither increments nor the liquid CHO at all help to improve
endurance times in athletes. It was found in this paper that liquid CHO did nothing more
than replenish the body during a race. Runners and cyclists may become dehydrated
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during an endurance test, and administering sports drinks will work to hydrate the runner
or cyclist. Hydration is not a major factor in endurance, as the muscles will still shut
down if the glycogen levels drop far enough.
As stated before, solid CHO takes a while to digest within the stomach, and this
will lengthen the endurance time. As the food sits within the stomach, it releases its
nutrients to the bloodstream in order to travel further down the gastrointestinal tract. The
carbohydrate nutrients, which supply glycogen to the muscles, take longer to get through
the bloodstream when the CHO is in solid form. This can be very beneficial because it
will bring glycogen stores to the muscles of the body for longer periods of time helping
the muscles to prevent shutdown. So by eating a meal rich in CHO an hour to four hours
prior to exercise, the runner or cyclist will have extra CHO stores during the desired
exercise. The CHO stores will eventually travel through the bloodstream to the muscles,
and provide the muscles with the glycogen that is needed to lower the muscle fatigue
level. When this happens, the runner or cyclist can run or ride for much longer periods of
time.
Liquid CHO, however, travels through the body fast. It provides the body with
the desired nutrients at the specific moment. As previously observed, liquid CHO is most
effective to replenishing the body to prevent dehydration, not muscle fatigue. However,
liquid CHO would be most effective at preventing muscle shutdown over a shorter period
of time. For sprinters, liquid CHO would be beneficial to ingest prior to and during
exercise in small increments. It would work fast through the body to provide muscles
with a quick burst of glycogen to go an extra mile or an extra minute. Also for body
builders, a quick energy burst is just enough for the muscles to work that much harder
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and that much longer to lift a certain amount. For this argument paper though, it makes
the most sense mechanistically that solid forms of CHO will work the longest to provide
the muscles with glycogen stores in order to prevent fatigue and in doing so increase the
endurance time.
In conclusion, because of the strong methods, the variety in CHO observed to be
effective, and how the CHO works mechanistically, solid CHO is superior to liquid CHO
in improving endurance times in runners and cyclists. These endurance athletes need the
desired supplement to prevent fatigue and ensure proper glycogen storage. Solid CHO
does the best at preventing fatigue and limiting the glycogen depletion over long periods
of time. Because of this, eating a meal or any other form of solid CHO is most effective
for runners and athletes regarding endurance.
Figures
1.
Work output
130,000
Work output (N*m)
125,000
120,000
115,000
110,000
105,000
Meal CHO
liquid CHO
type of CHO
This figure shows that the meal CHO work output is larger than the liquid CHO work
output.
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2.
Maximal test time
200
180
160
test time (min)
140
120
100
80
60
40
20
0
solid CHO
liquid CHO
type of CHO
This figure shows that when ingesting liquid CHO, the maximal test time possible is
higher than when ingesting solid CHO.
3.
total exercise time
270
260
exercise time
250
240
230
220
210
200
cereal
placebo
type of CHO
This figure shows that when the cereal was ingested, the exercise time increased
significantly compared to the placebo.
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4.
run time to exhaustion
180
160
run time to exhaustion (min)
140
120
100
80
60
40
20
0
pasta
supplement
type of CHO
This figure shows in the blue the different groups of the 50% CHO diet. The red is the
different groups of the 90% CHO diet. There is a slight difference between the pasta and
supplement in the 50% diet as shown.
References
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& Sidossis, L.S., (2004). Effect of maltose-containing sports drinks on exercise
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