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Les avantages de la maltodextrine

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Les avantages de la maltodextrine

Messagepar Nutrimuscle-Conseils » 7 Jan 2009 13:47

Les avantages de la maltodextrine

Orienteering performance and ingestion of glucose and glucose polymers

Br. J. Sp. Med; Vol 23

U.M. Kujala, MD1'2 O.J. Heinonen, MD1 M. Kvist, MD1, O-P. Karkkainen, MSC3 J.


The benefit of glucose polymer ingestion in addition to 2.5
per cent glucose before and during a prolonged orienteering
competition was studied. The final time in the competition
in the group ingesting 2.5 per cent glucose (group G,
n=10) was 113 min 37 s±8 min 11 s, and in the group which
had additionally ingested glucose polymer (group G+GP,
n=8) 107 min 18s±4 min 41 s (NS). One fifth (21 per cent) of
the time difference between the two groups was due to difference
in orienteering errors. Group G+GP orienteered
the last third of the competition faster than group G
(p<0.05). The time ratio between the last third of the
competition and the first third of the competition was lower
in group G+GP than in group G (p<0.05). After the competition,
there was statistially insignificant tendency to
higher serum glucose and lower serum free fatty acid
concentrations in group G+GP, and serum insulin concentration
was higher in group G+GP than in group G
(p<0.05). Three subjects reported that they exhausted during
the competition. These same three subjects had the lowest
serum glucose concentrations after the competition (2.9
mmol.1-', 2.9 mmol.1-', 3.5 mmol.l-') and all of them were
from group G. It is concluded that glucose polymer syrup
ingestion is beneficial for prolonged psychophysical performance.



Introduction
Orienteering is a sport in which the orienteer has to
find his way through unfamiliar terrain from one
control (checkpoint) to another with a map and a
compass. The result of a competition thus, in addition
to physical capacity, also depends on the level of planning
and other orienteering skills as well as on the ability
to maintain the concentration level. In top level
orienteers the 02 consumption and heart rate are quite
even and about 90 per cent of the maximal
capacity during competitions"2. Throughout a long
competition, both the heart rate and the blood lactate
concentration are higher than the anaerobic threshold
determined in laboratory conditions2. The high heart
rate during an orienteering competition may be
explained by central stimuli3 in addition to the loading
of several different muscle groups at the same time
with uneven rhythm when running in difficult terrain.
Dietary carbohydrates and fluids during prolonged
endurance exercise enhance performance. The two
most important factors limiting prolonged, strenuous
exercise are believed to be dehydration and depletion
of muscle glycogen stores. During prolonged exercise
a muscle can increase its net blood borne glucose uptake
10- to 20-fold above the resting value4. Decrease in
blood glucose concentration and simultaneous decrease
in prolonged physical performance level are observed,
although the primary factors limiting performance are
not known exactly5. The effect of lowered blood glucose
levels on performance level in skill sports through
inadequate nutrition of the brain is also discussed6.
Glucose is the major energy source for the brain7. The
brain cannot store this carbohydrate, which means
that the cerebral metabolism is critically dependent
upon freely circulating ambient blood Flucose in order
to maintain normal neuronal function .
Gastric emptying is controlled for example by osmoreceptors
in the duodenum9. Gastric emptying rate
seems to be the primary limiting factor in delivering
water, carbohydrate, and minerals to the body10,
hyperosmolalic solutions being unfavourable. Glucose
polymers appear to be favourable because their osmolality
is low, while high amounts of carbohydrates are
delivered into the intestine.
However, on the basis of recent studies, there is
some disagreement whether carbohydrate feeding
during prolonged exercise enhances performance
by preventing the depletion of muscle glycogen
stores1' 12. The greatest volume of the repeated bolus
and its greatest carbohydrate concentration than can
simultaneously deliver fluid and enhance performance
is not known"3. There is also wide individual
variation in gastric emptying and intestinal transport
Br. J. Sp. Med., Vol. 23, No. 2 105
Correspondence to: DR Urho Kujala, Paavo Nurmi Centre, Sport
Medical Research Unit, Kiinamyllynkatu 10, SF-20520 Turku,
Finland
(© 1989 Butterworth & Co (Publishers) Ltd
0306-3674/89/020105-04 $03.00
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Orienteering performance: U. Kujala et al.
and also in other responses to fluid and substrate administration.
In 1986 there were 3151 ranked orienteers in the
male open class in Finland. We have analyzed the fluid
and carbohydrate use of orienteers in the Finnish
Championships and found it to be below the theoretically
optimal level. The aim of this study was to
analyze the benefit of more abundant energy and fluid
ingestion than is commonly used before and during
orienteering competition (prolonged psychophysical
performance) by using glucose polymers.
Subjects and methods
Eighteen male top level orienteers volunteered as subjects
for this study and gave their informed consent
(Table 1). The subjects were ranked between 4 and 157
in the Finnish ranking list, based in success in orienteering
competitions during previous months. The
orienteers were randomly divided into two groups.
Ten orienteers (group G) ingested before and during
their competition a total of 900 ml of 2.5 per cent glucose
according to a given schedule (Table 2). Eight
orienteers (group G+GP) ingested 900 ml of 2.5 per
cent glucose solution and additionally 400 ml of glucose
polymer syrup (Table 2). There was no significant
difference in the mean of the ranking positions between
the groups. Hence it was possible to obtain two groups
of the same performance level for this study. All subjects
orienteered the same course, which was 16 000
metres long when measured from one control to
another. The course had 24 control points and consisted
of three different parts (Figure 1).
From start to control 8 (4200 m), difficult (detailed)
orienteering
From control 8 to control 15 (7000 in), easy (rough)
orienteering
From control 15 to the finish (4800 m), difficult
(detailed) orienteering
Table 1. Age, height, weight and training of the athletes
G (n= 10) G+GP(n=8)
Age (years) 25.1±2.6 26.3±3.2
Height (cm) 181.8±6.5 182.7±4.9
Weight (kg) 69.7±5.7 67.9±5.5
Training 1986 (hours/week) 11.7±4.0 10.8±2.6
G; group ingesting 2.5% glucose solution
G+GP; group ingesting 2.5% glucose solution and glucose polymer
Mean±SD
Table 2. The study schedule
G G+GP
60 min before start blood sample A blood sample A
55 min before start 2.0 dl 2.5% gluc. 2.0 dl 2.5% gluc.
1.0 dl gluc. polym.
30 min before start 2.0 dl 2.5% gluc. 2.0 dl 2.5% gluc.
1.0 dl gluc. polym.
15 min before start 1.0 dl 2.5% gluc. 1.0 dl 2.5% gluc.
Control 8/4.2 km 2.0 dl 2.5% gluc. 2.0 dl 2.5% gluc.
1.0 dl gluc. polym.
Control 15/11.2 km 2.0 dl 2.5% gluc. 2.0 dl 2.5% gluc.
1.0 dl gluc. polym.
Finish/16 km blood sample B blood sample B
J Figure 1. Examples from the different thirds of the orienteering
course a: Detailed orienteering from the first third of the race;
b: Rough orienteering from the second third of the race;
c: Detailed orienteering from the last third of the race
The air temperature varied during the competition
between +5.5°C and +6.9°C and the relative humidity
between 50 per cent and 60 per cent.
The glucose polymer (maltodextrin) consisted of 5-7
glucose units/molecule (MXR; Huhtamaki OY Marli,
Finland). The glucose polymer syrup had 67 g
carbohydrates in 100 ml water and its osmolality was
674 mOsm/kg water. The average temperature of the
liquids ingested was 20°C. The scheme for group
G was chosen to correspond to the normal practice
among Finnish top level orienteers recorded in Finnish
Championships in 1986. When adjusting the
scheme of group G+GP, the practical possibilities in
normal orienteering competition had to be taken into
account.
Antecubital venous blood samples were taken one
hour before the competition (sample A) and 60-120 s
after the competition (sample B) (Table 2). Serum was
separated and stored in -20° until analysis. Immunoreactive
serum insulin (S-Ins) was determined by the
commercial RIA-method (Novo, Denmark), and
serum free fatty acids (S-FFA) were determined by enzymatic
colorimetric method (Nefa C, Wako Chemicals
GmbH, West Germany). A Transcon 102 FN
analyzer (Orion Analytica, Finland) was utilized for
combined enzymatic determination of serum glucose
(S-Gluc)14.
After the competition, the subjects answered a
structured questionnaire including data on previous
training and other background information, and comments
on aspects such as orienteering errors made and
gastrointestinal symptoms experienced during the
study competition. They also marked the exact route
that they had used on the maps. On the basis of this information
the time lost due to orienteering errors was
calculated. To evaluate the number of errors, the sum
score of orienteering errors was formed as follows:
1 point; small error; time loss 30 s - 2 min 30 s
2 points; moderate error; 2 min 30 s - 5 min
3 points; major error; more than 5 min
During the days preceding the study competition,
the subjects had a normal Finnish mixed diet; none of
the subjects underwent special carbohydrate loading.
106 Br. J. Sp. Med., Vol. 23, No. 2
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Orienteering performance: U. Kujala et al.
In the morning before the competition, the subjects
had a normal mixed light breakfast according to their
own habits, but including no more than 500 ml of
fluids.
Statistical differences were tested using the Mann-
Whitney U test and X2 test.
Results
One subject from both groups suffered from gastrointestinal
symptoms which lowered his performance.
On the basis of subjective opinions, three subjects in
group G and none in group G+GP reported feeling
exhausted during the competition.
There was no time difference between the groups in
the first third of the competition, but group G+GP ran
the last third in a shorter time than the control group G
(p<0.05), (Table 3). About one fifth (21 per cent) of the
total time difference between the groups was due to
difference in orienteering errors observed (Table 3).
The sum score of the errors during the last third of the
competition was 1.8±2.1 in group G and 1.4±1.3 in
group G+GP (NS). The time ratio between the last
third of the competition and the first third of the competition
was lower in group G+GP than in group G
(p<0.05), (Table 3).
After the competition, the serum insulin concentration
was higher in group G+GP than in group G
(p<0.05), (Figure 2). An insignificant trend to higher
serum glucose and lower serum free fatty acid concentrations
were correspondingly observed (Figures 3
and 4).
The lowest glucose concentration after the competition
in group G+GP was 4.8 mmol.l-', while in group
G there were two subjects with a glucose concentration
of 2.9 mmol.lP and one subject of 3.5 mmol.l'.
These three subjects orienteered the last third of the
competition proportionally more slowly than the
mean of group G, and they were also the same subjects
who reported that they had become exhausted during
the competition.
Discussion
Our study scheme was not assessed to be theoretically
optimal with reference to fluid and energy ingestion,
but the practical possibilities in an orienteering competition
has to be taken into account. For example, the
ingestion of carbohydrates 45-15 minutes before exercise,
which is common in orienteers, is not recommended
because it can cause hyperinsulinemia followed
Table 3. The time during the different thirds of the competition,
the time ratio between the last and first third of the competition,
the elapsed time and the estimated time lost due to orienteering
errors during different thirds of the competition in groups G and
G+GP (mean±SD) (*P<0.05, difference between the groups)
G (n= 10) G+GP(n=8)
Time I Start to control 8 (min.s) 31.07±1.48 30.52±1.39
Time II Control 8 to control 15 (min.s) 42.05±2.10 41.27±2.43
Time III Control 15 to finish (min.s) 40.25±6.40 34.59±1.59*
Time III/time I 1.30±0.21 1.14±0.08*
Total time (min.s) 113.37±8.11 107.18±4.41
Time lost due to errors 1 (min.s) 2.27±2.00 2.11 ± 1.33
Time lost due to errors 2 (min.s) 0.36±0.56 0.23±0.45
Time lost due to errors 3 (min.s) 1.56±2.50 1.05±1.15
20
_ 15
E
.3
0)
._c
Ce I0
5
Before
i-- P< 0.05
Figure 2. Serum insulin (S-Ins) concentration (mean±SEM)
60 min before and immediately after the competition
8
E
E
)
8~
4 Before After
2 .
Figure 3. Serum glucose (S-Gluc) concentration (mean±SEM)
60 min before and immediately after the competition
by hypoglycemia'5. In our study, pre-exercise carbohydrate
ingestion did not cause significant decrease
of endurance capacity in group G+GP when compared
to group F (Table 3). The group G+GP was
drinking 200 ml of a 2.5 per cent glucose solution and
100 ml of a 67 per cent carbohydrate solution at each
time point except for one. This effectively gives 300 ml
of a carbohydrate solution with a carbohydrate content
of 24 gm/100 ml. On the basis of laboratory experiments,
such a solution should be emptied reasonably
rapidly from the stomach and should be reasonably
well absorbed by the small intestine'.
There seems to be a more significant difference
between the groups in the final results of the orienteering
competition than in similar studies demanding
only physical performance capacity'2, although a dif-
Br. J. Sp. Med., Vol. 23, No. 2 107
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Br. J. Sp. Med., Vol. 23, No. 2
1.4
1 .2 ^ I~~~oT -1.0
E
E 0.8 -
cz 0.6 - After
0.4-
0.2 -
Before
Figure 4. Serum free fatty acids (S-FFA) concentration
(mean±SEM) 60 min before and immediately after the competition
ference in physical performance level has been noted
during exercise exceeding 90 min exercise also earlier5.
There is always a problem in attempting to compare
the performance of two different subjects.
Because we can also compare the results of the last
and the first thirds of the competition within both
groups, we can exclude the possibility that the time
differences between the groups are solely due to
groups selection. The number of orienteering errors
did not significantly differ between the groups, and
the group difference in the time lost due to orienteering
errors accounted for only one fifth of the total time
difference between the two groups. We suggest that
top level orienteers can concentrate and avoid making
serious errors even when the brain is working on
limited glucose. Thus one possible explanation for the
significant difference between the results can be attributed
to better nutrition of the brain. This is also in
agreement with the fact that those subjects whose
blood glucose concentrations were lowest at the finish
subjectively became exhausted and objectively had
longer elapsed times during the last third of the competition.
This theory also agrees with other earlier
studies in skill sports but more studies are required6.
It has been suggested that, when the initial glycogen
levels are elevated, carbohydrate ingestion during
exercise does not result in a significant saving of muscle
glycogen or performance improvement during a
two-hour exercise period". We suggest that adequate
carbohydrate ingestion using glucose polymers during
long competitions is beneficial. In addition to increasing
performance level, the use of glucose polymers
might also hasten recovery, which is supported by a
smaller decrease in S-Ins concentration, and also by a
smaller increase in the plasma vasopressin concentration
in group G+GP than in group G (p<O.OO1), which
was recorded in the association with this study'6. We
did not measure muscle glycogen concentration,
because taking the samples would have significantly
disturbed the performance of the subjects in our study
schedule, a fact we discovered in our pilot study.
We conclude that the ingestion of glucose polymer
with 2.5 per cent glucose solution as one alternative in
carbohydrate feeding during high level prolonged
psychophysical performance is well tolerated and
beneficial. On the basis of our study we recommend
that more refreshment controls be provided in orienteering
competitions.
Acknowledgements
The authors thank the Finnish Central Sports Federation
and the Finnish Orienteering Association for their
financial support. Our acknowledgement is also due
to Erkki Alanen for the statistical work in the study.
References
1 Eklund, B., Hulten, B., Lundin, A., Nord, L., Saltin, B.
and Silander, L. (Eds.) 'Orienteering' Trygg-Hansa,
Stockholm, 1973
2 Karkkainen, O. P. (Ed.) 'Analysis of orienteering competition'
(in Finnish) Faculty of Physical and Health
Education, University of Jyvaskyla, Jyvaskyla, 1986
3 Morgan, W.P. Psychogenic factors and exercise
metabolism: a review Med Sci Sports Exerc 1985, 17, 309-
316
4 Wahren, J., Felig, P., Ahlborg, G. and Jorfeldt L. Glucose
metabolism during leg exercise in man I Clin Invest
1971, 50, 2715-2725
5 Ivy, J.L., Miller, W. and Dover, V. Endurance improved
by ingestion of a glucose-polymer supplement
Med Sci Sports Exerc 1983, 15, 466-471
6 Shephard, R.J. and Leatt, P. Carbohydrate and fluid
needs of the soccer player Sports Med 1987, 4, 164-176
7 Arky, R.A. 'Hypoglycemia' In Endocrinology (vol. 2)
G.F. Cahill, W.D. Odell, L. Martini, J.T. Potts, D.H.
Nelson, E. Steinberger, A.I. Winegrad (Eds.), Grune
and Stratton, New York, 1979
8 Ingvar, D.J. and Lassen, N.A. (Eds.) 'Brain work: The
coupling of function, metabolism and blood flow in the
brain' Academic Press, New York, 1975
9 Hunt, J.N. and Knox, M.T. 'Regulation of gastric emptying'
In Handbook of physiology (vol. 4) C.F. Code (Ed.),
American Physiological Society, Washington DC, 1968
10 Wheeler, K.B. and Banwell, J.G. Intestinal water and
electrolyte flux of glucose-polymer electrolyte solutions
Med Sci Sports Exerc 1986, 18, 436-439
11 Flynn, M.G., Costill, D.L., Hawley, J.A., Fink, W.J.,
Neufer, P.D., Fielding, R.A. and Sleeper, M.D. Influence
of selected carbohydrate drinks on cycling performance
and glycogen use Med Sci Sports Exerc 1987, 19,
37-40
12 Noakes, T.D., Lambert, E.V., Lambert, M.I., McArthur,
P.S.,Myburgh, K.H. and Benade, A.J.S. Carbohydrate
ingestion and muscle glycogen depletion
during marathon and ultramarathon racing Eur I App
Physiol 1988, 57, 482-489
13 Mitchell, J.B., Costill, D.L., Houmard, J.A., Flynn,
M.G., Fink, W.J. and Beltz J.D. Effects of carbohydrate
ingestion on gastric emptying and exercise performance
Med Sci Sports Exerc 1988, 20, 110-115
14 Lowry, O.H. and Passonneau, J.V.(Eds.) 'Flexible system
of enzymatic analysis' Academic Press, New York,
1972
15 Costill, D.L. Carbohydrates for exercise; dietary demands
for optimal performance Int I Sports Med 1988, 9,
1-18
16 Viinamaki, 0., Heinonen, O.J., Kujala, U.M. and
Alen, M. 1988 Glucose polymer syrup attenuates
strenuous physical exercise-induced vasopressin release
Acta Physiol Scand 1988, 134,(575), 103
108 Br. J. Sp. Med., Vol. 23, No. 2
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Messagepar Nutrimuscle-Conseils » 7 Jan 2009 13:55

Sugars for success?
Ian Macdonald, MD, DSc, PhD


As long ago as the 1930s it was known that dietary
carbohydrates enhance physical performance, especially in
prolonged exercise. It was also known that in intense
exercise over short periods the fuel used by active muscle is
solely glycogen. Unfortunately, the amount of glycogen
stored in muscle is limited (800 kCal). As this glycogen is
being used up, body fat has to be broken down in order to
provide for the continuing need for muscle contraction.
When fat becomes the prime source of muscle energy, a
marked drop in muscle efficiency occurs. This not only
means that more energy has to be spent to achieve the same
output, but also that the individual becomes ketotic.
The aim, therefore, is to make sure the supply of muscle
glycogen does not get depeleted. This applies especially to
long term events. Furthermore, as the body cannot convert
body fat or dietary fat to glycogen or glucose, and as dietary
protein is needed for other metabolic tasks, this leaves only
the carbohydrate in the diet as a major source of energy for
the muscles. Carbohydrates in the diet come in many forms
from complex starches to simple sugars such as sucrose,
glucose and fructose.
Short duration exercise
This is usually associated with high intensity activity. The
higher the intensity, the greater the muscle glycogen used
and the less fat is used as an energy source; above a V02
max of 95 per cent, glycogen exclusively is used. Thus a fast
pace in the early stages of exercise will lead to rapid muscle
depletion.
Moderate duration exercise of up to 60 to 90 minutes is
unlikely to be influenced by carbohydrate intake during the
event and so it need not be considered further. However,
the presumption in making this statement is that the
glycogen store in the active muscles is full of glycogen at
the commencement of the moderate duration event. It
should be remembered that in many short term events the
athlete has to compete several times a day in heats. This
will involve topping-up the musde glycogen between
events.
The value of training in short duration events, whereby
fatigue is delayed and power output is improved, is due
largely to the higher levels of glycogen in muscle when
trained. The influence of frequent exercise, which leads to
repeated bouts of musde glycogen reduction, results in
increasing the glycogen level in muscle. This glycogen must
come from the carbohydrate in the diet. Furthermore, the
amount of glycogen in muscle has a direct effect on
maximal power output. The success or otherwise in any
event may well be decided by the levels of musde glycogen
at that time.
Long duration exercise
It has been stated that when exercise is carried out at 50 per
cent V02 max or more, complete replacement cannot occur
during the exercise. But at lower levels of musde output,
the muscle glycogen can be renewed if the nutritional
intake is right. Obviously, the basic source of muscle
glycogen is the glucose in the blood. If the fall in blood
glucose concentration which is often seen in endurance
events can be prevented, then this should be encouraged.
The physiological picture is complicated by insulin. The
higher the level of blood glucose, the greater the output of
insulin. Insulin is helpful in that it encourages muscles to
take up glucose. However, it does have a disadvantage too.
A rapid output of insulin can lead to hypoglycaemia. This
is obviously not conducive to good athletic performance.
Carbohydrate loading
In 1939, it was observed that men on a high carbohydrate
diet for three days performed heavy workloads for more
than twice as long as men on a high fat diet for a similar
period. Presumably this was due to a greater content of
muscle glycogen while on the high carbohydrate diet.
Thirty years later it was proposed that the best way to
achieve maximum glycogen loading in preparation for an
endurance event would be first of all to deplete the muscles
of glycogen by exhaustive training. The low glycogen levels
would increase the activity of glycogen synthetase, an
enzyme which converts blood glucose to muscle glycogen.
Then, when a high carbohydrate diet was given just before
the endurance competition, the muscle stores of glycogen
would be higher than normal. It worked. Muscle glycogen
stores were twice as high as normal and endurance was
considerably increased.
The original regimen for building up these raised muscle
glycogen stores was fairly drastic and gave rise to athletes
becoming irritable, hypoglycaemic, unable to train and
subject to overstress injuries. It has subsequently been
learnt that neither the glycogen depletion by excessive
exercise, nor the three days of low carbohydrate diet are
necessary. Now the endurance trained athlete is able to
double his muscle glycogen level by resting for two or three
days while eating a diet rich in carbohydrate (8/10 g
CHO/kg BW/day).
Glycogen in the body, whether in the liver or in muscle,
is stored with about three times its weight of water.
Carbohydrate loading may produce a one to two kilogram
increase in body weight. It has been suggested that an

individual's body weight, taken after emptying the
bladder, may provide an indication of glycogen stores.
The limitations of this carbohydrate loading need to be
spelled out. First, it is of no value for events lasting less
than 90 minutes. Those lasting two to four hours are ideal
for this procedure. It is unwise for older athletes, as chest
pains and abnormal ECGs have been reported. It may give
rise to muscle damage, severe depression and stomachache
especially if the original regimen is used. There is also
evidence that, if the carbohydrate loading technique is
repeated too often, it fails to work. Perhaps it should be
used no more than two to three times a year.
It may be that carbohydrate loading can, to some extent,
be replaced by a high carbohydrate diet whose energy
content is equal to that of the energy expenditure during
the exercise. To eat over 500 g carbohydrate a day, as may
be required by a 70kg person may not be pleasant unless
much of that carbohydrate load is provided as simple
sugars, especially sucrose or as complex carbohydrates,
e.g. bread, potatoes or rice.
Carbohydrate feeding immediately before
exercise
In a recent study, 10 well trained male cyclists were given,
four hours before the exercise, a meal containing 200g of
carbohydrate in the form of cereal, bread, milk and fruit
juice. Then, five minutes before exercising they were given
a solid carbohydrate cereal bar. This regimen of a meal four
hours before, followed by the solid carbohydrate five
minutes before the event, resulted in significantly greater
oxygen consumption. Of more immediate importance, it
enhanced work output.
During exercise
The consumption of carbohydrates or any other nutrient
during exercise has for long received the armchair criticism
that all the blood goes to the muscles and that little goes to
the gut. As a result, little, if any nutrient will be absorbed
during musde activity. This is good theoretical physiology,
but in practice is incorrect. It was first shown several years
ago when the world cross-country ski championships were
won, for several years successively, by Sweden whose team
had been advised to take sugars at a level greater than
previously recommended during this long duration event.
It is now widely accepted that frequent ingestion of
glucose, or preferably a glucose polymer
, during an event is
a necessity. What is open to discussion is the amount and
frequency, bearing in mind that adequate water ingestion is
the top priority in any endurance event and far more likely
to impair performance than any lack of carbohydrate.
Therefore, during exercise, unlike pre-exercise, the carbohydrate
should be in solution or accompanied by water.
It has been suggested that glucose is of limited value as it
seems to remain in compartments within an unavailable
pool in the body during exercise. This discrepancy in
opinon may be due to the strength of the glucose solution
given. It seems, from several studies, that one gram of
glucose polymer, not glucose as such, in 5 ml water is
physiologically and metabolically acceptable. The story
about reactive hypoglycaemia may be exaggerated.
There are several reports where glucose, glucose
polymer, and fructose solutions have been given at 30
minute intervals during endurance exercise. All report an
improvement in performance compared with placebo,
using solutions varying from 15 to 30 per cent carbohydrate.
There is no doubt that glucose polymer given orally
is completely available for use by active muscle during
moderate to long-duration exercise.
In summary, during events lasting longer than between
60 to 90 minutes, 50 g of glucose polymer as a 20 per cent
solution should be taken every 30 minutes by an adult.
Glucose as such is not to be recommended because of its
rather unpleasant taste and high osmotic pressure.
Post-event carbohydrate ingestion
Many athletes have to compete again within 24 hours or so
of an event, perhaps even 12 hours later. It is essential that
the muscle glycogen stores are restored to full capacity as
soon as possible. The muscle glycogen store is more
receptive to oral carbohydrate immediately after the end of
exercise than, say, four hours later. As athletes are not keen
to ingest anything immediately after an event, persuasion
is required!
Thus, it is necessary to consider the following time
sequences when offering advice on dietary energy intake:
Several days before the event (carbohydrate loading)
Immediately prior to the event
During the event
Immediately after the event.
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Messagepar Free » 8 Jan 2009 18:18

Nutrimuscle-Conseil, Merci mille fois de nous faire partager ces études ! C'est super intéressant...
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Messagepar Adil » 8 Jan 2009 19:48

En gros il est plus interessent de consommer un sucre complexe tel que la maltodextrine plutot qu'un sucre rapide comme le dextrose ?
Adil
 
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Messagepar Nutrimuscle-Conseils » 9 Jan 2009 05:45

Adil a écrit:En gros il est plus interessent de consommer un sucre complexe tel que la maltodextrine plutot qu'un sucre rapide comme le dextrose ?


pour la différence, la perf est de 5 % meilleure avec la maltodextrine sur des épreuves de 2 heures chez des sportifs de haut niveau :

Glucose polymer syrup attenuates prolonged endurance exercise-induced vasopressin release.
Acta Physiol Scand. 1989 May;136(1):69-73. Viinamäki O, Heinonen OJ, Kujala UM, Alén M.


We investigated the effect of glucose and glucose polymer ingestion on plasma arginine vasopressin (pAVP) levels, on plasma osmolality (p-osm), and on performance during two prolonged endurance events. The study subjects were 37 Finnish elite endurance athletes, of whom 18 were orienteers and 19 cross-country skiers. Plasma AVP increased in both combined glucose and glucose polymer groups, but the increase in the glucose polymer group was significantly smaller (P less than 0.001) than that in the glucose group. A significant change in p-osm caused a significant change in pAVP and vice versa. Both the orienteers and the skiers on glucose polymer tended to have more success in the competition; the orienteers on glucose polymer ran the last third of the competition significantly faster than those on glucose (P less than 0.05). It is suggested, in the light of the smaller pAVP response, that after glucose polymer ingestion the physical stress in prolonged endurance exercise is smaller than after ingestion of glucose.
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Messagepar Adil » 9 Jan 2009 17:40

5% c'est toujours bon à prendre

Mais partant de cette réflexion peut-on en déduire que les polymères de glucides possédant un poids moléculaire plus important que celui de la maltodextrine comme le waxy ou le ***** sont encore plus efficaces ? Ou je m'égare ?
Adil
 
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Messagepar Nutrimuscle-Conseils » 9 Jan 2009 19:45

on a pas de donné concernant la performance de la part du *****
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