Cycling

Chapter 43
Cycling
ASKER E. JEUKENDRUP
Introduction
Without doubt, cycling is the sport most intensively studied by exercise physiologists and
sport nutritionists. Christensen and Hansen
(1939) were among the first to report the effect of
different diets on cycling performance. These
early reports already demonstrated the importance of carbohydrates (CHO) for improving or
maintaining exercise performance. Since then,
many studies have investigated the effect of
CHO feedings during cycling, and the role of
CHO after exercise to replenish glycogen stores
and improve recovery (see Chapters 5–8). This
chapter will review some of the nutritional habits
of cyclists and will define some recommendations for nutrition during bicycling races or
intensive training. Although cycling obviously
has many disciplines (including road racing,
time trialing, track cycling, mountain biking,
BMX), this chapter will focus on road racing and
time trialling.
Energy cost of cycling
Cycling, triathlon and cross-country skiing are
among the sports with the highest reported
energy turnovers. The levels of energy expenditure in these endurance sports have been measured in the field by using doubly labelled water,
an accurate technique which allows measurements over longer periods (days) in the field
(Westerterp et al. 1986). Of particular interest are
the data obtained during the most demanding
562
cycling race in the world: the Tour de France
(Saris et al. 1989). This race has 20 stages and lasts
about 3 weeks in which the riders cover almost
4000 km. During these 3 weeks, energy expenditures of up to 35 MJ · day-1 (8300 kcal · day-1) have
been reported during the long (300 km) stages
(Saris et al. 1989). Recently, we performed measurements of power output during the stages of
the Tour de France using a power-measuring
system (SRM Training System, Germany) which
is claimed to be accurate to ± 1%, and to record
and store power data at 1-s intervals (G. Leinders
& A.E. Jeukendrup, unpublished findings).
These data show that average power output
during a 6-h stage may be over 240 W, which
indicates a very high energy turnover. With an
estimated average efficiency of 22%, this represents an energy expenditure of about 24 MJ
(5700 kcal) during the race itself. In order to
maintain energy balance, a similar amount of
energy has to be consumed on a daily basis.
Most of the energy intake is derived from CHO
(Saris et al. 1989), which is less energy-dense
than lipid, and many CHO-rich foods are bulky
and rich in fibre. A high-CHO/high-energy diet
entails a large food volume and considerable
eating time. Since cyclists in the Tour de France
are usually on the bike for 4–6 h · day–1 and they
avoid eating 1–3 h before the start, there is barely
time left to eat the large meals. Besides this,
appetite is usually depressed after strenuous
exercise. These factors make it very hard to maintain energy balance on a daily basis.
Studies on energy balance have usually
cycling
employed indirect calorimetry or doubly
labelled water as techniques to measure energy
expenditure, while energy intake is usually estimated by the reported food intakes of athletes.
The reported energy intakes, however, display
large variation and are susceptible to a number of
methodological errors. Besides that, there are
only a few studies available in the literature
which systematically looked at the food intake of
cyclists. Nevertheless, the few available studies
report mean energy intakes which are similar
to those of other groups of endurance athletes
and which range from 15 to 25 MJ · day-1 (3500–
6000 kcal · day-1) for male athletes (Erp van-Baart
et al. 1989), cyclists in the Tour de France and
563
Tour de l’Avenir having the highest energy
intakes (Table 43.1).
During the Tour de France, mean food intake was 24.3 MJ · day-1 (5800 kcal · day-1) while
the highest recorded values reached 32.4 MJ
(7600 kcal) on the days of the long (300 km) stages
(Saris et al. 1989). This indicates that the athletes
in the Tour de France match their energy expenditures quite well with their food intake (Fig.
43.1), and they remain weight stable (i.e. maintain energy balance) during the entire race. Only
during the long stages with extremely high
energy expenditures could food intake not completely compensate for the energy expended. In
general, riders in the Tour de France remain
Fig. 43.1 Daily energy
expenditure (䊉) and energy intake
(䊊) as measured in a cyclist
during the Tour de France. The
profile of the race as well as the
length of the stages are indicated
at the bottom of this figure. r, days
of rest. From Saris et al. (1989).
35
35
30
30
25
25
20
20
15
15
Alps
12.5
Day 1 2 3 4
6
r
7
r
8
9 10 11 12 13 14 15 16 17 18 19 20 21
r
500 km
Table 43.1 Daily energy expenditures (EE) and energy intakes (EI) in cyclists.
NR, not recorded.
12.5
Race/category
EE
EI (MJ)
Reference
24-h race
Race across America
Tour de France (peak)
Tour de France (mean)
Tour de France
Tour de l’Avenir
Amateur cyclists
NR
NR
32.7 MJ
25.4 MJ
NR
NR
NR
43.4
35.4
32.4
24.7
24.3
23.3
18.3
Lindeman et al. 1991
Lindeman et al. 1991
Saris et al. 1989
Saris et al. 1989
Van Erp-Baart et al. 1989
Van Erp-Baart et al. 1989
Van Erp-Baart et al. 1989
Energy intake (MJ)
Energy expenditure (MJ)
40
564
sport-specific nutrition
remarkably weight stable (Saris et al. 1989; A.E.
Jeukendrup & G. Leinders, unpublished findings). Anecdotal evidence suggests that racers
who lose weight may not be able to finish the
race.
Brouns and colleagues (Brouns et al. 1989b–d)
performed a simulation study in the laboratory
in which the effect of diet manipulation was
studied in athletes expending 26 MJ · day-1
(6200 kcal · day-1) by exercising for 5 h in a respiration chamber. Subjects received ad libitum a
conventional solid diet with a high carbohydrate
content (62.5% CHO diet) supplemented with
water or the same diet supplemented with a 20%
CHO solution (80% CHO diet). Although food
intake was allowed ad libitum in both trials, the
CHO supplement enabled the subjects to maintain their daily energy balance, which they could
not when supplemented with water. As a consequence, exercise performance was improved.
These data show that during stage races or multiple days of intensive training, energy expenditure is very high and CHO-containing drinks
may be required to maintain energy balance in
cyclists involved in such rigorous programmes,
since digestion and absorption of solid meals
will be impaired and hunger feelings are suppressed during intensive physical exercise
(Brouns 1986).
Other reports in the literature regarding
energy intake of cyclists include those of the Race
Across America, a race from the West coast to the
East coast of the United States (Lindeman 1991).
Energy intake in one individual taking part in
this race was 35.4 MJ (8429 kcal) daily of which
78% was derived from CHO. During the preparation, this individual rode a 24-h race where
his energy intake was as much as 43.4 MJ · day-1
(10 343 kcal · day-1) with 75% of the energy from
CHO.
Eating behaviour of cyclists
An important observation from several of the
investigations which have reported very high
energy intakes in athletes is that a significant
amount of the day’s nutrient intake may be con-
sumed while the individual is exercising. For
example, CHO-rich foods and drinks consumed
while riding provided nearly 50% of the total
energy, and 60% of the daily CHO intake of
cyclists competing in the Tour de France stages
(Saris et al. 1989). Only by adopting such a nutritional regimen do these cyclists maintain energy
balance over the 20 days of the Tour de France.
Suitable food choices to attain such goals include
concentrated sports drinks and portable CHOrich foods such as fruit, confectionery, bread,
cakes and sports bars. It has also been reported
that a large part of the carbohydrates is from
snacks. These snacks usually contain simple carbohydrates, a fair amount of fat and little or no
micronutrients, and therefore it has often been
recommended that riders should replace these
snacks by fruit and snacks that contain less fat
and more micronutrients (Brouns 1986).
Preparing for a race
Athletes involved in prolonged moderate- to
high (> 70% of maximal oxygen uptake) intensity
exercise not only have unusually high energy
requirements but they also have greatly
increased CHO needs. The extra CHO is necessary to optimize fuel availability during training
sessions used, and to promote postexercise
muscle glycogen resynthesis. A well-known
method to restore glycogen levels to the preexercise level or even above that is known as
glycogen loading or glycogen supercompensation.
Glycogen loading
Muscle glycogen depletion and low blood
glucose levels have been shown to be major
factors in the development of fatigue during
endurance exercise. It is therefore important to
ensure optimal glycogen storage prior to exercise
and optimal delivery of CHO during exercise.
These aspects have been discussed in detail
in Chapter 7. Supercompensation protocols
as described by Bergström and Hultman
(Bergström et al. 1967) and later adapted by
cycling
565
Fig. 43.2 Pre-exercise feedings
will top up liver glycogen. Photo
© Cor Vos.
Sherman et al. (1981) do not usually apply to
cycling at the highest level. Professional cyclists
and top-level amateurs have too many races in a
short time period and a week of nutritional
preparation is usually not possible. For this
group of cyclists, it is often recommended that
they eat high-CHO diets which are often
expressed in percentages of CHO in daily energy
intake. However, the absolute amounts may be
more important. In a 70-kg subject, the body
CHO stores are believed to amount to about
600–700 g (about 10 g · kg–1 body weight). It is
believed that ingesting more than 600–700 g
(10 g · kg–1 body weight) of CHO to replenish
these stores will not further improve glycogen
storage (Rauch et al. 1995). This is especially
important for sports with repeated days of exercise with very high energy expenditures, such as
in the Tour de France (Saris et al. 1989). If these
athletes would consume a 70% CHO diet (as
often recommended), they would consume more
than a kilo of CHO, assuming an energy intake of
25 MJ (6000 kcal).
Recently, however, we observed increased
glycogen storage after ingestion of 12–13 g · kg-1
body weight · day-1 compared to 9 g· kg-1 · day-1
when athletes trained on a daily basis (A.E.
Jeukendrup et al., unpublished observations).
Prerace feedings
It is often recommended that CHO ingestion
should be avoided in the hours preceding the
race in order to prevent rebound hypoglycaemia.
CHO ingestion 30–120 min prior to exercise
raises plasma glucose and insulin levels, which
stimulates glucose uptake and inhibits fat mobilization and oxidation during exercise. Early
studies showed that CHO ingestion in the fasted
state, about 45–60 min prior to an acute bout of
exercise, may result in a drop in the blood
glucose concentration as soon as exercise begins
(Foster et al. 1979; Koivisto et al. 1981). During
intense exercise, this was shown in one study to
result in hypoglycaemia and decreased performance (Foster et al. 1979). However, more recent
studies, in the fasted state (Gleeson et al. 1986) as
well as in the non-fasted state, as is usual in athletes going into competition, have not shown
these detrimental effects (Brouns et al. 1991). Due
to strong individual differences in response,
however, it is always possible that an individual
is prone to an exercise-induced insulin rebound
response after a CHO-rich solid or liquid meal. In
addition, pre-exercise CHO feedings 2–4 h before
the race may inhibit lipolysis, decrease the availability of plasma fatty acids and thereby deprive
566
sport-specific nutrition
the muscle of substrate. This, in turn, may accelerate glycogenolysis and increase whole-body
CHO oxidation. Large pre-exercise CHO feedings may compensate for the excess oxidized
CHO by providing sufficient glucose through the
blood, whereas small CHO feedings may not
provide sufficient substrate and result in premature glycogen depletion and fatigue. So, preexercise CHO feedings should be large enough
(> 200 g) to provide substrate to the muscle to
compensate for the accelerated glycogen breakdown and increased CHO oxidation.
Recommendations for
precompetition nutrition
1 Ensure a CHO intake of 10 g · kg–1 body
weight · day–1 during the 3 days before the race.
This amount of CHO should maximize glycogen
storage.
2 Drink plenty of fluids during the days before
the race, to ensure euhydration at the start. If
large sweat losses are to be expected, add a little
sodium (a pinch of salt) to the drinks.
3 Avoid food with a high dietary fibre content
during the days before the competition to
prevent gastrointestinal problems.
4 Eat a CHO-rich meal 2–4 h before the race to
replenish the liver glycogen stores: before short
races, light digestible CHO foods or energy
drinks; before long races, semisolid or solid food
such as energy bars and bread. Too much protein
and fat should be avoided since this may slow
gastric emptying and may cause gastrointestinal
discomfort. This meal should contain a fair
amount of CHO (> 200 g) to compensate for the
increased glycogen breakdown and CHO
oxidation.
5 Although in general the intake of CHO in the
hours before a race does not have adverse effects
on performance, some individuals may develop
rebound hypoglycaemia when ingesting a highCHO meal or drinks before the race. These
individuals should delay eating CHO until the
warming up or 5 min before the race. An oral
glucose tolerance test can be used to determine
which individuals are prone to develop rebound
hypoglycaemia.
Nutrition during exercise
Nutrition during exercise longer than 90 min
CHO ingestion during exercise has been shown
to improve exercise performance in events of
90 min duration and longer by maintaining high
plasma glucose levels and high levels of CHO
oxidation. The increased availability of plasma
glucose enables the athlete to postpone fatigue or
to develop a higher power output in a final sprint
following endurance exercise (Hargreaves et al.
1984; Coggan & Coyle 1987, 1988, 1989; Mitchell
et al. 1988; Goodpaster et al. 1996). From numerous studies, we know that most of the soluble
CHO (glucose, maltose, sucrose, glucose polymers, soluble starch) are oxidized at similar rates,
as reviewed by Hawley et al. (1992), and similar
improvements in cycling performance have been
observed when ingesting glucose, maltodextrins
or soluble starch (Goodpaster et al. 1996). Exceptions are fructose, galactose and insoluble starch,
which are oxidized at slightly lower rates (Saris et
al. 1993; Leijssen et al. 1995) and do not seem to
have the same positive effect on performance
(Goodpaster et al. 1996). Therefore, glucose,
maltose, sucrose, glucose polymers and soluble
starch are all good CHO types to ingest during
exercise. Ingested CHO may be oxidized at rates
up to 1 g · min–1, which appears to be the maximal
exogenous CHO oxidation rate (for review, see
Hawley et al. 1992). Recently, we reported that
the oxidation rate of ingested CHO was similar
in well-trained cyclists and untrained individuals when they are exercising at the same relative
intensity and same rates of total CHO oxidation
(Jeukendrup et al. 1997b). The oxidation of exogenous CHO seems related to the amount ingested
(up to a certain limit) and the exercise intensity
and active muscle mass rather than any other
variables. Its maximal oxidation rate may be
determined by the absorption rate or by liver
metabolism (Jeukendrup 1997; Jeukendrup et al.
1999). However, additional research is required
to study the factors limiting exogenous CHO
oxidation. In order to maximize the contribution
of oral CHO to total energy expenditure, it may
be advised that 1–1.2 g CHO · min–1 (60–70 g · h–1)
cycling
should be ingested during exercise while slightly
higher rates of ingestion during the first hour
may speed up the achievement of these high
levels of oxidation. However, ingesting more
than 1.5 g · min–1 during exercise may not
result in increased exogenous CHO oxidation
(Wagenmakers et al. 1993) and increases the risk
of gastrointestinal problems.
Most studies of cyclists have shown that CHO
ingestion does not alter the rate of muscle
glycogen breakdown during exercise, although
during intermittent exercise glycogen may be
resynthesized during the low-intensity cycles
(Hargreaves et al. 1984; Kuipers et al. 1986). So the
mechanism by which CHO ingestion during
cycling improves performance in road races may
not only be maintaining the plasma glucose concentration, but also the resynthesis of muscle
glycogen during periods of low intensity.
Nutrition during high-intensity exercise
of about 1 h
Although previous studies suggested that CHO
feedings can improve exercise performance
during exercise of longer than 90 min duration,
recent evidence shows that CHO feedings can
also be effective during high-intensity exercise of
shorter duration (60 min) (Anantaraman et al.
1995; Below et al. 1995; Jeukendrup et al. 1997a).
567
We recently found improved time-trial performance (comparable to a 40-km time trial) in
well-trained cyclists when they ingested a
carbohydrate–electrolyte solution during exercise (75 g of CHO) compared with placebo (Fig.
43.3) (Jeukendrup et al. 1997a). Seventeen out of
19 subjects showed improved time-trial performance, while two athletes displayed a decreased
performance with the carbohydrate–electrolyte
solution. The average power output during the
time trial when the carbohydrate–electrolyte
solution was ingested was 298 ± 10 W vs. 291 ±
10 W with placebo. Although the beneficial effect
of the CHO ingestion during high intensity exercise of about 1 h duration has now been confirmed by several studies, the mechanism behind
this performance effect remains unclear and
central effects of glucose on the brain cannot be
excluded at this point (Jeukendrup et al. 1997a).
Optimally, athletes should ingest a carbohydrate–electrolyte solution throughout exercise in
order to maintain a certain volume of fluid in the
stomach which will enhance gastric emptying
(Rehrer et al. 1990). It has recently been shown
that ingestion of CHO throughout exercise
improves performance more than ingestion of an
identical amount of CHO late in exercise
(McConell et al. 1996). Again, these results
suggest that CHO ingestion improves performance through mechanisms other than, or in
68
Time to complete work (min)
Fig. 43.3 Ingestion of a
carbohydrate–electrolyte (CE)
drink reduces time to complete a
set amount of work (analogues to
completion of a 40-km time trial).
(a) Individual data of 17 male (䊉)
and 2 female athletes (䊊); (b) the
means.
Time to complete work (min)
61
65
62
60
58
55
Placebo
(a)
CE
60
59
58
57
(b)
Placebo
CE
568
sport-specific nutrition
addition to, an increased CHO availability to the
contracting muscles.
Medium-chain triacylglycerol ingestion
during exercise
Recently it has been suggested that mediumchain triacylglycerol (MCT) ingestion during
cycling exercise may provide an additional fuel,
thereby possibly sparing endogenous CHO
stores and improving exercise capacity. MCT is
derived from coconut oil and contains mediumchain fatty acids which are rapidly absorbed and
oxidized (Massicotte et al. 1992; Jeukendrup et al.
1995, 1996a). However, despite its rapid metabolism, several studies show that ingestion of small
amounts of MCT (25–45 g of MCT over the course
of 1–3 h) may not be sufficient to alter fat oxidation, glycogen breakdown or cycling performance (Ivy et al. 1980; Jeukendrup et al. 1995,
1996a, 1996b, 1998). Larger amounts generally
cause gastrointestinal problems and can therefore not be recommended.
Fluid intake during exercise
Besides CHO, cyclists need to maintain their
water balance. Exercise-induced dehydration
may augment hyperthermia and multiple
studies show that prevention of dehydration by
fluid ingestion improves performance (see
Chapter 16). Dependent on the weather conditions, fluid losses may vary from 0.5 to up to
almost 3 l · h–1. Individual fluid loss can be estimated from weight loss although this also
includes a small amount of weight loss due to
glycogen and fat oxidation. During 90 min of
exercise, 100–300 g of glycogen and fat may be
oxidized. By regularly monitoring body weight
before and after training sessions and competitions, it is possible to predict the fluid loss in a
certain race. However, since the main limitation
seems to be the amount of beverage that can be
tolerated in the gastrointestinal tract, in most
conditions it is advisable to drink as much as possible. Completely compensating for sweat loss
by fluid consumption may not always be pos-
sible because sweat losses may exceed 2 l · h–1 and
ingestion of such amounts cannot be tolerated by
the gastrointestinal tract. Observations in professional cyclists during the Mediterranean Tour in
France and the Ruta del Sol in Spain show that
riders lose about 2.1–4.5 kg during a 4–5-h stage,
indicating that even cyclists who are well aware
of the importance of drinking cannot drink sufficiently during a race (G. Leinders & A.E.
Jeukendrup, unpublished findings). Therefore,
fluid and CHO consumption is usually limited
by the practical situation and by the amount of
drink that can be tolerated after ingestion. This
highlights the importance of making ‘drinking
during exercise’ a part of the regular training
programme.
Also during high-intensity exercise of about
1 h duration, water seems to be beneficial to performance. Below et al. (1995) showed that water
ingestion, independently of CHO, improved
time-trial performance (time trial of about 10 min
.
duration after 50 min at 80% Vo2max.), while
the CHO and water had an additive effect on
performance.
Palatability of drinks and food is a very important aspect because it will stimulate consumption
and with it increase the intake of fluid and CHO.
In addition, taste and flavour perception may
also influence the rate of gastric emptying.
Disliked flavour or aroma may slow gastric
emptying and may even cause nausea.
Nutrition during exercise: some observations
in professional cyclists
In general, professional cyclists tend to eat solid
food during the first hours of their stages, usually
consisting of chunks of banana, apple, white
bread with jamor rice cakes. The pace during the
first hours is usually slow and there is plenty of
time to digest the solid food. As soon as the speed
increases, the cyclists switch to fluid ingestion
and solid food will only be eaten when the speed
drastically drops or their stomachs feel empty.
Since they have only two bottles on their bike,
usually containing 0.5 l each, they have to get
new bottles regularly during the race. Profes-
cycling
569
Fig. 43.4 Feeding zone where
bags with solid and liquid food
are given to the riders. Photo ©
Cor Vos.
sional cyclists often receive their new bottles
from the team director in the car behind the pack.
One or two riders of the team will go to the car
and bring bottles for the whole team. Also they
usually have the opportunity to get additional
bottles at the feeding zone (2–4 h into the race). At
these feeding zones the athletes will receive a
little bag containing one or two bottles of fluid
and some solid food in case they get hungry or
get an empty feeling in their stomach (Fig. 43.4).
Often riders will take the bottles and throw away
the solid food.
Recommendations for nutrition
during exercise
1 During intense exercise lasting 45 min or
more, a CHO solution should be ingested. This
may improve performance by reducing/delaying fatigue.
2 Consume 60–70 g CHO · h–1 of exercise. This
can be optimally combined with fluid in quantities related to needs determined by environmental conditions, individual sweat rate and
gastrointestinal tolerance.
3 During exercise of up to 30–45 min duration,
there appears to be little need to consume CHO.
4 The type of soluble CHO (glucose, sucrose,
glucose polymer, etc.) does not make much dif-
ference when ingested in low to moderate quantities. Fructose and galactose are less effective.
5 Athletes should consume CHO beverages
throughout exercise, rather than only water early
in exercise followed by a CHO beverage late in
exercise.
6 Avoid drinks extremely high in CHO and/
or osmolality (> 15–20% CHO) because fluid
delivery will be hampered and gastrointestinal
problems may occur.
7 Try to predict the fluid loss during endurance
events of more than 90 min. The amount of fluid
to be ingested should in principle equal the predicted fluid loss. In warm weather conditions
with low humidity, athletes have to drink more
and the drinks can be more dilute. In cold
weather conditions, athletes will drink only
small amounts and drinks have to be more
concentrated.
8 Large drink volumes stimulate gastric emptying more than small volumes. Therefore,
it is recommended to ingest a fluid volume of 6–
8 ml · kg–1 body weight 3–5 min prior to the start
to ‘prime’ the stomach, followed by smaller
volumes (2–3 ml · kg–1 body weight) every
15–20 min.
9 The volume of fluid that athletes can ingest is
usually limited. Athletes should ‘learn’ to drink
during exercise. This aspect can be trained.
570
sport-specific nutrition
10 After drinking a lot, the stomach may feel
empty and uncomfortable. In this case it may be
wise to eat some light digestible solid food
(CHO). During long, low-intensity races, solid
food can be eaten also in the first phase of the
race.
11 Factors such as fibre content, protein content,
high osmolality and high CHO concentrations
have been associated with the development of
gastrointestinal symptoms during exercise, and
thus should be avoided during exercise.
Nutrition after exercise
Quick recovery is an extremely important aspect
of training and frequent competitions. Especially
during repeated days of training or in stage
races, it is important to recover as quickly as possible. Dietary measures have been shown to
influence recovery significantly. The restoration
of muscle glycogen stores and fluid balance after
heavy training or competition is probably the
most important factor determining the time
needed to recover. The rate at which glycogen
can be formed (synthesized) is dependent on
several factors:
1 The quantitative CHO ingestion.
2 The type of CHO.
3 The timing of CHO ingestion after exercise.
4 Coingestion of other nutrients.
Amount of CHO ingestion
The quantity of CHO is by far the most important
factor determining the rate of glycogen resynthesis. In studies, it appeared that the muscle glycogen resynthesis rate of 50 g CHO ingested every
2 h was double that of 25 g CHO ingested every
2 h (Blom et al. 1987; Ivy et al. 1988b). When more
than 50 g was ingested (100–225 g), muscle glycogen storage did not further increase (Blom et al.
1987; Ivy et al. 1988b). Thus, 50 g in 2 h (or
25 g · h–1) appears to result in a maximum rate
of postexercise muscle glycogen resynthesis.
Frequent small meals do not appear to have an
advantage over a few large meals.
Type of CHO
To optimally restore glycogen levels after exercise, a source of CHO which is easily digested
and absorbed is needed. The rate of absorption
of a certain CHO is reflected by the glycaemic
index. Foods with a moderate to high glycaemic
Fig. 43.5 Rehydration and
carbohydrate loading start
immediately after the race. Photo
© Cor Vos.
cycling
index enter the bloodstream relatively rapidly,
resulting in a high rate of glycogen storage.
Foods with a low glycaemic index enter the
bloodstream slowly and result in a lower rate of
glycogen resynthesis. Therefore it is recommended that low glycaemic index foods should
not comprise the bulk of CHO after exercise
when a quick recovery is required.
Timing of CHO intake
During the first hours following exercise, glycogen resynthesis proceeds at a somewhat higher
rate than later on (Ivy et al. 1988a). Therefore, in
cases of short recovery times, CHO intake should
take place immediately after exercise. Although
this can maximize the rate of glycogen resynthesis in the early phase, the full process of glycogen
storage still takes considerable time. Depending
on the degree of glycogen depletion and the
type of meals consumed, it may take 10–36 h to
refill the glycogen stores to pre-exercise values.
Therefore, it is impossible to perform two or
more workouts per day without affecting the
initial glycogen stores. Even when CHO intake
between training bouts or competitions is very
high, the muscle glycogen levels will be suboptimal when the next activity is started within
8–16 h.
The rate at which fluid balance can be restored
depends on (i) the quantity of fluid consumed
and (ii) the composition of the fluid, especially
the sodium content. Recent studies show that
the postexercise fluid retention approximates
50% when the fluid that is consumed is low in
sodium. This is the case with most tap and
mineral waters as well as fruit juices. After the
consumption of carbohydrate–electrolyte solutions containing 25–100 mmol · l–1 sodium, the
water retention may be as high as 70–80%
(Maughan & Leiper 1995; Shirreffs et al. 1996).
From these findings, it can also be concluded
that, in order to restore fluid balance, the postexercise fluid consumption must be considerably
higher (150–200%) than the amount of fluid lost
as sweat.
571
Practical considerations
Usually, appetite is suppressed after exercise and
there is a preference for drinking fluids rather
than eating a meal. Therefore, beverages which
contain high-glycaemic-index CHO sources in
sufficient quantity (6 g · 100 ml–1 or more) should
be made available.
If preferred, the athlete may also ingest
easily digestible solid CHO-rich food such as
ripe banana, rice cake and sweets. When the
desire for normal meals returns, approximately
10 g CHO · kg–1 body weight of moderate- to
high-glycaemic-index CHO sources should be
eaten within 24 h. This can easily be realized by
consuming foods that are low in fat. For practical
reasons, a certain amount of low-glycaemic CHO
cannot be excluded from the diet.
Sleeping hours interrupt the feeding possibilities. Therefore, it is recommended to ingest an
amount of CHO prior to sleeping which is sufficient to supply the required 25 g · h–1 (e.g. 250 g
for a 10-h period).
Guidelines for postexercise nutrition
1 To maximize glycogen storage, it is recommended to ingest 100 g CHO during the first 2 h
after exercise in the form of liquids or easily
digestible solid or semisolid meals. In total,
about 10 g CHO · kg–1 body weight should be
eaten within 24 h, with two thirds of this preferably as high glycaemic index foods.
2 It is recommended to consume CHO sources
with moderate to high glycaemic index to hasten
recovery.
3 Addition of 25–100 mmol · l–1 sodium to postexercise rehydration beverages improves fluid
retention and the recovery of fluid balance.
Acknowledgements
The author would like to thank Dr G. Leinders
and the Rabobank professional cycling team for
their friendly co-operation.
572
sport-specific nutrition
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