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Dextrose + maltodextrine 15 min avant l'effort...

Messagepar Nutrimuscle-Conseils » 6 Fév 2009 11:14

Dextrose + maltodextrine 15 min avant l'effort augmente la performance de sprints répétés sur 1 h de :
- 9,5 % par rapport au fait de ne pas boire
- 8 % par rapport à de l'eau

The Effects Of Ingesting a Carbohydrate-Electrolyte Beverage 15 Minutes Prior
to High-Intensity Exercise Performance

G. W. Davison a; C. McClean a; J. Brown a; S. Madigan a; D. Gamble a; T. Trinick b; E. Duly b

Research in Sports Medicine, 16: 155–166, 2008

The aim of this study was to examine the effect of ingesting a commercially
available carbohydrate-electrolyte (CHO-E) solution on strenuous
exercise performance. Ten apparently healthy male volunteers (Mean ± SD;
age 20 ± 2 yrs; height 178 ± 7 cm; body mass 77 ± 10 kg; estimated VO2max
56 ± 3 ml×kg-1×min-1) completed three experimental trials in random
order separated by a minimum of 7 days. For each trial, subjects consumed
(8 ml×kg-1 body mass) either a CHO-E solution (6% carbohydrate,
50 mg Na/500 ml), a non-CHO-E placebo, or no fluid, 15 minutes prior
to exercise. The exercise involved intermittent shuttle (20 m apart)
running for 1 hr followed by an incremental shuttle running test to
exhaustion. Subjects displayed longer exercise times when the CHO-E
Received 1 November 2007; accepted 25 February 2008.
Address correspondence to Dr. G.W. Davison, Sport and Exercise Sciences Research
Institute, University of Ulster at Jordanstown, Newtownabbey, Co Antrim BT37 OQB.
E-mail: gw.davison@ulster.ac.uk
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156 G.W. Davison et al.
solution was ingested compared with placebo or no fluid groups (exercise
time to exhaustion – CHO-E 649 ± 95 s, vs. placebo 601 ± 83 s, vs. no fluid
593 ± 107 s, P < 0.05). There was a main effect for time for specific gravity
of urine (P < 0.05 vs. postexercise, pooled data) and body mass (P < 0.05 vs.
postexercise, pooled data). The main finding from this investigation
indicates that drinking a CHO-E solution 15 minutes prior to exercise
improves performance. This study has practical implications for those
sports where drinking during activity is restricted.
Keywords: glucose ingestion, blood glucose concentration, exercise performance
INTRODUCTION
It is well documented that carbohydrate ingestion before and during exercise
is effective at maintaining or improving exercise performance (Hargreaves,
Hawley, and Jeukendrup 2004; Jeukendrup 2004). An increase in exercise
intensity results in a parallel increase in carbohydrate utilisation by the working
muscles. Carbohydrate supplementation should therefore maintain the
necessary intramuscular levels of tricarboxylic acid cycle intermediates
required for the increase in energy expenditure (Hargreaves 1995).
The effects of carbohydrate ingestion on exercise have been extensively
researched (Ali et al. 2007; Fahey et al. 1991; Patterson and Gray 2007). In
1980, a study by Van Handel and colleagues demonstrated that ingested
glucose may appear within the peripheral circulation rapidly, but it is not
recovered in expired air, suggesting that carbohydrate consumed during
exercise is not used for the production of energy. In a more recent study,
however, the consumption of glucose during exercise has been reported to
improve performance in prolonged endurance activity (Tsintzas et al.
1993). In addition, it has been demonstrated that ingested glucose is effectively
oxidised and contributes to energy supply by preventing a decline in
blood glucose concentration (Wright, Sherman, and Derbach 1991), and
fatigue from possible hypoglycemia (Coyle et al. 1983; Hargreaves 1995).
Fluid consumption during prolonged exercise also has been shown to be
beneficial for attenuating dehydration and improving performance, possibly
by the effective actions of important electrolyte molecules such as the extracellular
cation sodium and the intracellular cation potassium.
Although the bulk of evidence suggests that the benefits of ingesting
carbohydrate is limited to exercise lasting more than 90 minutes, where
muscle glycogen depletion is a potential cause of fatigue (Coggan and
Coyle 1987), it is common practice for athletes performing for shorter
periods to ingest commercially available CHO-E drinks prior to exercise.
The ingestion of carbohydrate within the hour prior to exercise can cause
an increase in both blood glucose and insulin concentration. This may be
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Carbohydrate-Electrolyte Ingestion Prior to Exhaustive Exercise 157
detrimental to homeostasis at the onset of exercise as there is a rapid fall
in blood glucose as a consequence of the combined stimulatory effects of
hyperinsulinaemia and increased muscle contractile activity (Hargreaves
et al. 2004). Notwithstanding this, the metabolic alterations associated
with carbohydrate ingestion in the 30–60 minutes before exercise has the
potential to improve exercise performance (Gleeson et al. 1986; Kirwan,
O’Gorman, and Evans et al. 1998; Hargreaves et al. 2004), and on balance
there appears to be no justifiable reason as to why carbohydrate consumption
should be avoided within the hour before exercise (Hargreaves et al.
2004). There is a paucity of research, however, on the efficacy of ingesting
a commercially available CHO-E solution 15 minutes prior to but not
during exercise. Consistent with the literature, we hypothesise that performance
would be enhanced following the ingestion of a CHO-E solution
15 minutes prior to strenuous aerobic exercise. A randomised, cross-over,
double-blind, placebo-controlled experimental design was employed to
test this hypothesis.
METHODS
Subjects
Ten (n = 10) apparently healthy male recreationally active (not participating
in more than two exercise [running or cycling] sessions per week)
volunteers (Mean ± SD; age 20 ± 2 years; height 178 ± 7 cm; body mass
77 ± 10 kg; estimated VO2max 56 ± 3 ml⋅kg−1⋅min−1) completed this study.
The nature and risks of the experimental procedures were explained to all
subjects, and their written informed consent was obtained prior to testing.
All procedures were approved by the Research and Ethics Committee of
the University of Ulster.
Experimental Design
The study constituted a double-blind placebo-controlled, randomised
cross-over design. All subjects were familiarised with all testing procedures
prior to experimental trials. All trials were performed at the same
time of day to negate diurnal variation. For 3 days prior to the first experimental
trial, all subjects were required to follow their “usual” diet, and
weigh and record all foods consumed. The same diet then was consumed
before the second and third trials. In order to facilitate compliance, diet
sheets were given to each subject, which were brought to the first trial,
photocopied, and returned to the subjects to ensure replication. All subjects
completed three experimental trials in random order separated by a
minimum of 7 days. For each trial, subjects consumed (8 ml.kg−1 body
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158 G.W. Davison et al.
mass) either a CHO-E solution (Powerade, Coca-Cola; 6% carbohydrate,
50 mg Na/500 ml), a non-CHO-E placebo (consisting of water, citric acid,
flavouring, stabilisers, and sweeteners), or no fluid, 15 minutes prior to
exercise. The drinks were identical in taste, colour, temperature, and
texture, and they were presented in the same coloured containers for all
trials. Prior to the experimental trials, a limited subject number were
given a small amount of the experimental beverages, and indicated no
taste variation between the two drinks. Preceding each trial, subjects’
nude body mass and stature were measured to the nearest 0.1 kg and 0.1 cm,
respectively, using a freestanding stadiometer (Seca Delta-Model 707,
Cardiokinetics, UK).
Intermittent Exercise and Performance
The exercise involved intermittent shuttle (20 m apart) running for 4 × 15 min
blocks. Each block consisted of 10 90 s segments: 3 × 20 m walking, 1 × 20 m
maximum sprint, 3 × 20 m jogging, and 3 × 20 m fast running (Shirreffs
and Merson 2003). On completion of the final block, subjects commenced
the incremental shuttle running test to exhaustion (Ramsbottom, Brewer,
and Williams 1988). Heart rate (HR) was recorded continuously during
each trial by means of ECG calibrated telemetry (Polar Electro OY,
Kempele, Finland).
Blood and Urine Sampling
Venous blood was collected following a 12 hr overnight fast from an
antecubital forearm vein prior to fluid ingestion and exercise and
immediately postexercise using the VacutainerTM method (Becton-
Dickinson, Oxford, UK). Blood for potassium, trigycerides, and
sodium determination were collected in serum separation glass vacutainer
tubes (SST) and allowed to clot for 10 minutes in the dark.
Blood for glucose determination was collected in sodium fluoride
vacutainers containing dipottasium ethylene diamine tetra-acetic acid
(EDTA). After centrifugation at 3000 rpm at 4°C for 10 minutes, the
blood aliquots were stored at −80°C. All aliquots were assayed within
2 days of collection. All samples for the same subject were analysed
within the same batch. Resting and postexercise PCV (packed cell volume)
and Hb concentration was measured on whole blood to correct for
acute exercise-induced plasma volume shifts using the equations of
Dill and Costill (1974).
Hydration levels were monitored pre- and postexercise using a total
solids refractometer (specific gravity of urine; Leica, TS 400, Leica
USA).
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Carbohydrate-Electrolyte Ingestion Prior to Exhaustive Exercise 159
Biochemical Analysis
Blood Glucose, Serum Triglycerides, Sodium, and Potassium. Blood glucose
was determined by the immobilised enzyme membrane method in conjunction
with a Clark electrode using a standard glucose analyser (YSI 2300
Analyser, Yellow Springs, Ohio, USA). Triglycerides, sodium, and potassium
were measured from blood samples by enzyme assay using the AerosetTM
analyser (Abbott Labs, IL, USA).
Packed Cell Volume (PCV) and Haemoglobin (Hb). PCV (%) was measured
using the standard microcapillary reader technique, and corrected
by 1.5% for plasma trapped within erythrocytes (Dacie and Lewis 1968).
Haemoglobin (g/dL) was measured using a β-haemoglobin photometer
(Hemocue Ltd, Angelholm, Sweden).
Statistical Analysis
Statistical analysis was performed using the SPSS package (Version 11.0,
Surrey, UK). Data were analysed using parametric statistics following
mathematical confirmation of a normal distribution using repeated
Shapiro-Wilk W tests. A paired samples t test was used to compare
performance times and maximum heart rate values between groups, while
a two-way analysis of variance (ANOVA) that incorporated one within
(state: rest vs. exercise) and one between (group: CHO-E vs. placebo vs.
no fluid) subjects factors was used to compare HR, specific gravity of
urine, and body mass. Following a significant interaction effect (state ×
group), within subjects factors were analysed using Bonferroni-corrected
paired samples t tests. Between subject differences were analysed using a
one-way ANOVA with a post-hoc Tukey honestly significant difference
(HSD) test. The alpha was established at P < 0.05, and all values are
reported as a mean ± standard deviation (SD). The required subject number
was determined using the power calculations of Altman (1980).
RESULTS
Exercise Times to Exhaustion
The run times of the CHO-E, placebo, and no-fluid groups were 649 ±
95 seconds (s), 601 ± 83 s, and 593 ± 107 s, respectively. Thus, when
the subjects ingested the CHO-E solution they ran 47 s longer than the
placebo group (P < 0.05) and 56 s longer than the no-fluid group
(P < 0.05). There was no difference between the placebo vs. no-fluid
group (P > 0.05).
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160 G.W. Davison et al.
Blood Metabolites
Blood glucose concentrations were maintained within the normal range in
all three experimental conditions. It was higher in the CHO-E group
following glucose ingestion (P < 0.05), however, when compared with
the placebo and no-fluid groups (Figure 1). There were no differences
between groups for triglycerides (Figure 2), or for the electrolytes sodium
(Figure 3) and potassium (Figure 4; P > 0.05).
Specific Gravity of Urine
There was a main effect for time for specific gravity of urine (P < 0.05 vs.
postexercise, pooled data) as shown in Table 1.
Body Mass and Heart Rate
Table 1 demonstrates a main effect for time for body mass (P < 0.05 vs.
postexercise, pooled data). Maximum postexercise HRs for the CHO-E,
placebo, and no fluid groups were 196 ± 7, 192 ± 7, and 195 ± 6 b.min−1,
respectively. There were differences between the CHO-E vs. placebo
group (P < 0.05).
Figure 1. Blood glucose (mmol.L-1) concentration for the three experimental
conditions.
2
3
4
5
6
7
8
9
10
Pre-supplementation Pre-exercise* Post-exercise
Blood glucose (mmol.L–1)
Glucose drink
Placebo drink
No fluid
*Indicates a difference between presupplementation for glucose drink only (P < 0.05).
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Carbohydrate-Electrolyte Ingestion Prior to Exhaustive Exercise 161
DISCUSSION
The main finding of this study indicates that a CHO-E solution ingested
15 minutes prior to but not during intermittent and exhaustive exercise
delays fatigue and improves exercise performance. This improvement in
Figure 2. Serum triglyceride (mmol.L−1) concentration for the three
experimental conditions.
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
Pre-supplementation Pre-exercise Post-exercise
Triglycerides (mmol.L–1)
Glucose drink
Placebo drink
No fluid
Figure 3. Serum sodium (mmol.L−1) concentration for the three experimental
conditions.
133
134
135
136
137
138
139
140
141
142
143
144
Pre-supplementation Pre-exercise Post-exercise
Sodium (mmol.L–1)
Glucose drink
Placebo drink
No fluid
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162 G.W. Davison et al.
performance is consistent with other published literature (see Table 2
below for an overview of the literature); however, the majority of these
studies used an experimental protocol that involved the ingestion of
carbohydrates 30–60 minutes before exercise or immediately before and
during exercise.
Figure 4. Serum potassium (mmol.L−1) concentration for the three
experimental conditions.
2.5
3
3.5
4
4.5
5
5.5
6
Pre-supplementation Pre-exercise Post-exercise
Potassium (mmol.L–1)
Glucose drink
Placebo drink
No fluid
Table 1. Body Mass and Specific Gravity of Urine
Before and Following Exercise
Parameter Preexercise Postexercise
Body mass (kg)
Glucose drink 77 ± 10 75 ± 10
Placebo drink 75 ± 9 73 ± 9
No fluid 77 ± 10 75 ± 10
Main effect for time
Specific gravity of urine (units)
Glucose drink 1.005 ± 0.003 1.020 ± 0.01
Placebo drink 1.008 ± 0.004 1.013 ± 0.01
No fluid 1.008 ± 0.005 1.019 ± 0.008
Main effect for time
All values are means ± SD. Main effect for time indicates a
difference between preexercise vs. postexercise (pooled glucose,
placebo, and no fluid values), P < 0.05.
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Carbohydrate-Electrolyte Ingestion Prior to Exhaustive Exercise 163
There is a distinct lack of published literature demonstrating that
carbohydrate ingestion may be beneficial if consumed 15 minutes prior
to the start of intermittent and exhaustive exercise. Moreover, studies
determining the relationship between carbohydrates and intermittent
exercise performance usually favour the option of ingesting before in
addition to during exercise, while there is a need to ascertain if carbohydrate
supplementation prior to but not during intermittent exercise can
increase performance as effectively. For example, Nicholas et al. (1995)
administered a 6.9% CHO-E solution or a noncarbohydrate placebo
immediately before and every 15 minutes during intermittent exercise
and observed an increase in endurance running capacity. Shirreffs and
Merson (2003) used a design similar to the present investigation and
demonstrated an improvement in exercise to exhaustion following the
administration of a commercially available CHO-E drink 20 minutes
prior to and during exercise. The biochemical mechanisms associated
with an improvement in exercise performance as a consequence of
ingesting carbohydrates during intermittent exercise are reported to
include (1) the prevention of hypoglycaemia, (2) maintaining a high rate
of carbohydrate oxidation, and (3) possible glycogen sparing (Nicholas
et al. 1995).
We specifically chose to include an intermittent exercise protocol
before exhaustive exercise in order to attempt to decrease muscle glycogen
levels in all experimental groups, and therefore demonstrate that any
increase in performance during the exercise may be due to a greater availability
of blood glucose and possible sparing of muscle glycogen as a
result of carbohydrate ingestion. The results of this study may therefore
interest sports performers that do not have the opportunity to ingest fluids
during exercise, but have aspirations to delay fatigue and enhance performance
during high-intensity, prolonged exercise.
Table 2. Overview of Carbohydrate Ingestion Prior to Exercise Performance
Reference
Timing of carbohydrate ingestion
before exercise Exercise outcome
Nicholas et al. (1995) Immediately before and during exercise Increase in performance
Tsintzas et al. (1996) Immediately before and during exercise Increase in performance
Patterson and Gray (2007) Immediately before and during exercise Increase in performance
Shirreffs and Merson (2003) 20 minutes Increase in performance
Gleeson et al. (1986) 45 minutes Increase in performance
Kirwan et al. (1998) 45 minutes Increase in performance
Sherman et al. (1991) 60 minutes Increase in performance
Thomas et al. (1991) 60 minutes Increase in performance
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164 G.W. Davison et al.
Elevated blood glucose levels as a result of carbohydrate feeding
during exercise have consistently been reported (Chryssanthopoulos et al.
1994; Tsintzas et al. 1993). In the present study, there was a significant
increase in blood glucose concentration 15 minutes after carbohydrate
consumption. Seiple and colleagues (1983) suggest that CHO-E solutions
greater than 2.5% glucose may slow the gastric emptying process;
however, although gastric emptying was not measured in this study, it is
evident from Figure 1 that large quantities of the 6% glucose solution
were absorbed from the gastrointestinal tract and appear in the bloodstream.
During exercise, there was a marked decrease in blood glucose
concentration in the CHO-E group. This decline in blood glucose concentration
occurs as a result of elevated skeletal muscle blood flow during
exercise, and an increase in glucose extraction. This is primarily due to an
increase in glucose transport, and activation of the glycolytic and oxidative
pathways responsible for glucose disposal (Hargreaves 1995). Therefore,
it is reasonable to postulate that augmented carbohydrate availability
in the latter stages of exercise may have contributed to the overall
increase in performance as observed in the present study (Balmer et al.
1995; Wiber and Moffatt 1992).
Heart rate (HR) in all experimental groups increased linearly over the
course of exercise. A significant difference was found between
the CHO-E and placebo groups only, which may be accounted for by
the increased exercise intensity in the CHO-E group. The additional glucose
concentration in the peripheral circulation may have allowed the
subjects to increase exercise intensity, thereby delaying fatigue and
improving performance. This finding is in agreement with Williams and
colleagues (1990), who also demonstrated that glucose ingestion is
associated with an increase in HR and an improvement in exercise
performance. Although we did not quantify perceived rate of exertion, it
has been suggested that glucose consumption may affect brain neurotransmitters
(Maughan 1991) and therefore may alter the perception
of exertion, allowing the individual to exercise at a greater intensity.
The current study does not facilitate elucidation of the mechanisms
underlying this effect, however, and such explanations remain purely
speculative.
It is unlikely that the differences in exercise performance between the
CHO-E group and the other groups could be due to the consumption of
additional electrolytes, as there was no difference in potassium or sodium
concentrations between groups. Moreover, although the specific gravity
of urine increased postexercise, there was no difference in dehydration
between groups, and this is supported by no interaction effect observed
for body mass. Therefore, it is reasonable to suggest that it was the provision
of additional carbohydrates that complemented existing muscle
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Carbohydrate-Electrolyte Ingestion Prior to Exhaustive Exercise 165
carbohydrate stores, enabling the CHO-E group to delay the onset of
fatigue and exercise for longer (Nicholas et al. 1995).
In conclusion, the ingestion of a commercially available CHO-E drink
15 minutes prior to (but not during) the onset of exercise improves run
time to exhaustion, possibly as a result of maintaining blood glucose concentration
and increasing available energy to the working muscles. This
study has practical implications for those sports where drinking during
activity is restricted.
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