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Abstract

The goal of training is to prepare the distance athlete to perform at his or her best during major competitions. Whatever the event, nutrition plays a major role in the achievement of various factors that will see a runner or walker take the starting line in the best possible form. Everyday eating patterns must supply fuel and nutrients needed to optimize their performance during training sessions and to recover quickly afterwards. Carbohydrate and fluid intake before, during, and after a workout may help to reduce fatigue and enhance performance. Recovery eating should also consider issues for adaptation and the immune system that may involve intakes of protein and some micronutrients. Race preparation strategies should include preparation of adequate fuel stores, including carbohydrate loading for prolonged events such as the marathon or 50-km walk. Fluid and carbohydrate intake during races lasting an hour or more should also be considered. Sports foods and supplements of value to distance athletes include sports drinks and liquid meal supplements to allow nutrition goals to be achieved when normal foods are not practical. While caffeine is an ergogenic aid of possible value to distance athletes, most other supplements are of minimal benefit.
Nutrition for distance events
Louise M Burke1, Gregoire Millet2, Mark A Tarnopolsky3
1Department of Sports Nutrition, Australian Institute of Sport, Belconnen, Australia 2616
2 Department of performance enhancement, Aspire, PO Box 22287, Doha, Qatar
3 Departments of Pediatrics and Medicine, McMaster University, Hamilton, Canada.
Corresponding author:
Louise M Burke,
Department of Sports Nutrition,
Australian Institute of Sport,
Belconnen,
Australia 2616
Ph 61 2 6214 1351
Fax 61 2 6214 1603
Email: louise.burke@ausport.gov.au
Running title: Nutrition for distance events
Abstract:
The goal of training is to prepare the distance athlete to perform at his or her
best during major competitions. Whatever the event, nutrition plays a
substantial role in the achievement of various factors that will see a runner or
walker take the starting line in the best possible form. Everyday eating
patterns must supply fuel and nutrients needed to optimise their performance
during training sessions and to recover quickly afterward. Carbohydrate and
fluid intake before, during, and after a workout may help to reduce fatigue
and enhance performance. Recovery eating should also consider issues for
adaptation and the immune system which may involve intakes of protein and
some micronutrients. Race preparation strategies should include preparation
of adequate fuel stores, including carbohydrate loading for prolonged events
such as the marathon or 50 km walk. Fluid and carbohydrate intake during
races lasting an hour or longer should also be considered. Sports foods and
supplements of value to distance athletes include sports drinks and liquid
meal supplements to allow nutrition goals to be achieved when normal foods
are not practical. While caffeine is an ergogenic aid of possible value to
distance athletes, most other supplements are of minimal benefit.
Introduction
There are a large number of events which involve prolonged effort within the
IAAF umbrella of track and field, road running, cross country, and race-
walking. Events commonly undertaken by elite competitors include the 5,000
and 10,000 m track events, the half-marathon and marathon, the 20 and 50
km walks and cross-country runs (8 km for females and 12 km for males). In
addition, there is a vast array of “fun runs” and community events around the
world which can attract large fields ranging from the elite to the weekend
warrior. Nutrition plays a key role in assisting distance athletes of all levels to
achieve their training and competition goals.
Training for distance runners and walkers
Distance runners follow a periodised training program (see Stellingwerff et
al., 2007), split into base training (8 to 16 weeks), a precompetitive period (8-
6 weeks) and a competitive period (if track events) or a tapering phase (up to
3 weeks) prior to a marathon followed by a short transition/recovery phase.
Heat acclimatisation before competition in a hot environment and altitude
training are other specialised training techniques often undertaken by
distance runners and walkers. Altitude training remains a controversial area,
with coaches and scientists still arguing over the benefits of periods in a
hypoxic (lower oxygen) environment on performance at sea level. Distance
athletes who usually reside at low altitudes have a variety of options for
undertaking altitude training (see Hawley et al., 2007).
Since the athletes of East Africa origins (Kenya, Ethiopia and more recently,
Eritrea and Uganda) dominate distance running, the reasons for their
superiority have been extensively studied (Billat et al., 2003; Lucia et al.,
2007; Saltin et al. 1995). Among the key physiological factors of distance
running performance (i.e. VO2max, the maximal fraction of VO2max sustained
during the event, the velocity at lactate threshold and the running energy
cost), it appears that they have mainly a greater running economy (Lucia et
al., 2006) and a higher fractional utilisation of VO2max than Caucasian runners
(Saltin et al., 1995; Lucia et al., 2006). The underlying mechanisms of these
differences are still contradictory but are a combination of social, genetic and
anthropometric/biomechanical factors. The effects of the altitude
residence/training per se or of nutritional differences have not been identified.
Although a high running distance in training (80-150 km.wk-1 in 3,000–5,000
m runners; 150-220 km.wk-1 in marathon runners during base training) is
commonly observed in all distance runners, several studies have reported
that most African runners spend a larger part of their weekly training at high
relative intensity. The current trend in distance running is to a ‘polarised
training’ model; i.e. a large percentage (70-75%) at strictly aerobic intensity,
a small percentage (<10%) of ‘Tempo’ training at around or above lactate
threshold and 15-20% at high intensity.
Competition in distance events
Although most distance events involve a single race, there are some events
which require heats and finals (e.g. 5,000 and 10,000 m on the Olympic
Games and World Championship programs). Most distance runners and
walkers peak for several important events in a year (e.g. a Big City Marathon
or the World Championships). However, there may be other situations in
which they compete in a series of races including the lucrative professional
circuit in Europe, meets within a university circuit such as the NCAA season,
or in the cross-country schedule for club athletes. In general, the main
competition for track and field occurs in summer, whereas cross-country has
an autumn and/or winter season. Most road races attracting large fields of
both elite and community-based participants are scheduled over the warmer
months from spring to late autumn where heat and hydration become more
of an issue. The schedule of Big City Marathons, which includes races in
Boston, Chicago, New York, London, and Paris, extends from April to
November.
Aerobic metabolism typically accounts for more than 95% of the energy cost
of long-distance events, especially half-marathon and marathon races and
the longer walking events. However, there are critical times in all distance
races requiring anaerobic effort—for example, a surge, a hill, or a sprint
finish—that may be the ultimate factor in determining the order of race
finishers. The factors that limit the performance of distance runners and
walkers vary according to the duration and environment of the race and
nutrition is an important factor in success over the duration of the event.
Because many of these factors—such as fluid balance, the availability of
carbohydrate fuel, and even the disturbance to acid-base status arising from
anaerobic glycolysis—can be manipulated by dietary strategies, nutrition is
an important component of the athlete’s preparation for competition.
Nutritional Issues and Challenges
There is a range of common nutritional issues that arise in long-distance
running and walking as a result of issues related to optimal physique,
training, and race day performance. This review will provide an overview of
the major issues.
Physique
Very low levels of body fat are a striking feature of successful distance
athletes. However, it is hard to distinguish whether this is a critical factor in
determining successful performance or the outcome of the high training
volumes needed for successful performance. Low levels of both total mass
(which determines the total energy cost of running) and fat mass (dead
weight that must be transported) assist fast and economical movement.
These traits become even more important when the event involves long
distances or moving against gravity (e.g., running up hills in a road or cross
country race). Because upper-body musculature is unimportant for running
performance, elite runners and walkers typically exhibit minimal evidence of
muscle development in their arms and upper torso. Although there is
variability in the size of long-distance runners and walkers, the winners of
“hot weather” races tend to be small and light. A small and compact
physique offers thermoregulatory advantages, both by reducing the absolute
amount of heat that is produced (smaller muscle mass) and by achieving a
more efficient dissipation of heat generated by the body (enhanced ratio of
surface area to volume). There are data from both modelling (Dennis and
Noakes, 1999) and laboratory (Marino et al., 2000) sources to show that
lighter runners store less heat at the same running speed and enjoy an
advantage in conditions where heat dissipation mechanisms are at their limit.
Some runners and walkers achieve a small and very lean frame as a result of
their genetic background and training program. However, other runners with
naturally larger frames or higher levels of adiposity feel that they must whittle
themselves down to an “unnatural” size and body fat level to be competitive.
Although many male runners eat and train specifically to reduce their body
fat and racing weight, the battle for a low percentage of body fat and weight
control is most often identified as a female problem. This may be because
females generally need to push their body characteristics further from their
natural shape than male runners to achieve the leanness that is considered
ideal. Attempts to deviate body fat further from the apparent biological
“default” can have negative effects, including “penalties” resulting from the
low body fat levels per se such as a lack of insulation against cold. Other
penalties arise from the nutrition and training methods used to manipulate
weight and body fat including restricted intakes of energy, protein,
carbohydrate and micronutrients (Burke, 2007). Some athletes develop frank
medical or psychiatric problems such as eating disorders, osteopaenia and
chronic menstrual dysfunction. More develop sub-clinical versions of these
problems; the spectrum of restrained eating, menstrual dysfunction and poor
bone health within the “female athlete triad” is covered in greater detail by
Manore et al. (2007) and similar issues should also be considered in the
evaluation of some male athletes.
The problems associated with poor bone health lie not only with the risk of a
premature onset of osteoporosis but also with the immediate problem of
stress fractures. Recurrent or chronic stress fractures can prevent the
athlete from competing at important times and interfere with his or her ability
to undertake the training volume necessary for high level performance. Many
athletes have had promising careers ended by this injury pattern. Distance
runners and walkers should be encouraged to set realistic weight and body
fat goals; these are specific to each athlete and must be judged by trial and
error over a period of time. Further discussion on dietary strategies to assist
with loss of weight and body fat is found in the review by O’Connor et al.
(2007).
Poor iron status
There is a common belief that endurance athletes, particularly distance
runners, are at high risk of iron deficiency; this has been given apparent
credibility because the target levels for iron status measures such as serum
ferritin are often set well above those of normal population standards to
provide a “safety margin” for athletes whose performance are underpinned
by the roles of iron in oxygen transport (haemoglobin and myoglobin) and
enzyme function (for review, see Deakin 2006).
The depletion of the body’s iron stores progresses through a number of
stages with different functional and diagnostic criteria (see Deakin 2006). The
literature is unclear, in part because of methodological concerns, whether
iron depletion, in the absence of anaemia impairs exercise performance
(Fogelholm 1995). Some studies of iron supplementation in iron-depleted but
non-anaemic female runners (Klingshirn et al. 1992; Newhouse et al. 1989;
Powell and Tucker 1991) failed to find differences in performance changes
between supplementation and placebo treatment groups, even when serum
ferritin increased with iron therapy (Klingshirn et al. 1992; Newhouse et al.
1989). However, in other studies, female runners with low ferritin levels
experienced a performance improvement, albeit in conjunction with an
increase in haemoglobin levels, after iron supplementation (Lamanca and
Haymes 1993; Schoene et al. 1983). Of course, athletes are also concerned
whether iron depletion affects their ability to recover between workouts or
races. Brownlie et al. (2004) exposed previously untrained participants with
non-anaemic iron depletion to a 4-week training program and found that
those with a tissue iron deficiency (based on abnormal serum transferrin
receptor concentrations) had an impaired adaptation to this training
compared with a similar group who received iron supplements. In contrast,
iron supplementation did not affect endurance cycling performance at the
end of the training program in the iron-depleted group who were not tissue
iron-depleted.
In summary, the true prevalence of iron-deficiency anaemia in distance
runners and walker is probably not greater than in the general population
(Fogelholm, 1995). However, reduced iron status does occur and may be
problematic for performance or adaptation to training, particularly altitude
training (see Hawley et al., 2007). The cause is essentially the same reason
that it occurs in the general population: a lower than desirable intake of high
bioavailability iron. Iron requirements may be increased in distance athletes
because of increased gastrointestinal or haemolytic iron losses (for review
see Deakin, 2006). However, the most important risk factor is still the low-
energy or low-iron diet. Females, vegetarian eaters, and those following diets
with restricted quantity and variety are at highest risk. Dietary interventions to
reverse or prevent a decline in iron status involve strategies to increase total
iron intake as well as to increase the bioavailability of this iron.
The management and prevention of iron deficiency requires careful diagnosis
using a variety of clinical, haematological, dietary, and medical data.
Haematological and biochemical tests that are routinely measured to indicate
iron status should be undertaken in a way that minimises or standardises the
effect of exercise on the results. In athletic populations, ferritin levels lower
than 30-35 ng/ml (Nielsen and Nachtigall 1998) are generally marked for
further consideration or review, especially where it makes a change in the
established iron status history of the individual. New tests including the
measurement of serum transferrin receptors and the characteristics of
reticulocytes may offer new opportunities. However, these tests are not
routinely available in all laboratories and need to be studied carefully in
relation to iron status in athletes.
Many distance athletes are tempted to self-medicate with iron supplements
that can be purchased over the counter. However, there are several risks
involved with the consumption of iron supplements in the absence of a
confirmed iron status problem, including haemosiderosis or iron overload.
Typically, a 3-month period of supplementation, in the form of a daily dose of
100 mg of elemental iron, is needed to restore depleted iron stores (Nielsen
and Nachtigall 1998). In some cases, when it is not possible to enhance
dietary iron intake sufficiently, iron supplementation is continued at a lower
dose to prevent ongoing iron drain. In cases of extreme iron depletion or
where oral iron intake is not tolerated, intramuscular injections of iron can
achieve a rapid increase in iron stores. However, there is no evidence of
additional performance benefits over oral supplementation, and there are
higher risks of side effects. Iron injections will not increase haemoglobin
levels or other iron parameters in people who are not otherwise suboptimal in
iron status (Ashenden et al. 1998).
Carbohydrate needs for optimal training and recovery
Distance runners and walkers must be able to rapidly recover their muscle
fuel stores between daily or twice-daily sessions, and between races on the
competition circuit. A high-carbohydrate intake enhances the performance of
a single bout of prolonged running as well as the recovery and performance
of a subsequent running bout (Fallowfield and Williams, 1993). However,
muscle glycogen concentrations may not completely recover over 24 to 48 h
following a very strenuous running session (e.g., marathon) or unaccustomed
eccentric loading, despite a plentiful carbohydrate supply (Asp et al. 1997;
Sherman et al. 1983). Unaccustomed muscle damage may cause a
disruption to muscle cell function and may require an increase in total
carbohydrate intake in the first 24 h of recovery (Doyle et al. 1993) or a
greater recovery time (up to 7 days) for full replacement of muscle glycogen.
Logically, benefits from enhancing acute recovery between sessions should
translate over time into better training adaptations and long-term
performance gains. However, the literature, which includes three studies
involving runners, is curiously unclear in showing that high carbohydrate
diets provide superior training outcomes to moderate carbohydrate intakes
(Burke, 2007). Kirwan and colleagues (1988) studied well-trained runners
who increased their training by 150% for 5 days while consuming either high
(8 g/kg/d) or moderate (4 g/kg/d) intakes of carbohydrate. Muscle glycogen
concentration gradually declined in both treatments but was better preserved
with the higher carbohydrate diet; additionally, running economy at two
different running speeds was better. By contrast Sherman and colleagues
(1993) followed 7 days of training in two groups of runners who consumed
daily carbohydrate intakes of either 5 g/kg (gradually reduced muscle
glycogen levels) or 10 g/kg (maintained muscle glycogen concentrations). At
the end of this period, the groups did not differ in their capacity to undertake
two treadmill runs to exhaustion at 80% VO2max with a short recovery
interval at the end of a training session.
Finally, well-trained runners undertook 7 days of intensified training
supported by both moderate- (5.4 g/kg/d) and high- (8.5 g/kg/d) carbohydrate
diets (Achten et al. 2004). Muscle glycogen utilisation decreased during
submaximal running on the moderate-carbohydrate diet and there was a
decline in speed over 8 km (treadmill) and 16 km (outdoor) time-trials.
However, the high-carbohydrate treatment was associated with a smaller
decrease in 8 km speed and maintenance of 16 km performances. The
authors concluded that a high-carbohydrate diet reduced symptoms of
overreaching in runners during intensified training compared with a
moderate-carbohydrate diet but could not prevent it entirely.
An emerging interest is that of dietary periodisation – the so-called “train low,
compete high” approach - in which distance athletes deliberately train with
low glycogen or carbohydrate availability to enhance metabolic adaptations
to the training stimulus, then replete carbohydrate to enhance their
competition performance (see Hawley et al. 2007). Currently, there is
inadequate scientific support to recommend that distance athletes should
practice carbohydrate restriction for prolonged periods Indeed, the potential
disadvantages of this practice include an increased risk of illness and injury
(see Nimmo et al., 2007) and reduced well-being or capacity to train (see
Burke and Kiens, 2006). In fact, the available study supporting a “train low”
approach (Hansen et al., 2005) achieved glycogen depletion for some, but
not all, training sessions by manipulating the training time table rather than
dietary intake. Indeed, it is likely that elite athletes spontaneously periodise
carbohydrate availability within their microcycles of training because the
practicalities of their lifestyle and training mean that some sessions are taken
after an overnight fast, or without complete refuelling between workouts.
Unless more sophisticated research can identify benefits from deliberately
“training low”, distance athletes should eat to promote carbohydrate
availability, at least for the most important training sessions of the week.
Recent recommendations for daily carbohydrate intake (Burke et al., 2004)
acknowledge that fuel requirements for distance athletes differ according to
body size and training loads. The targets of 7-10 g/kg/d for high volume
training and 5-7 g/kg/d for more moderate exercise loads provide a general
target that must be fine-tuned according to overall nutritional goals and
performance feedback from each athlete. Such recommendations may be
unfeasible for runners, particularly females, whose focus on low body mass
and body fat levels requires energy restriction and, by association, a lower
carbohydrate intake. The compromise is to periodise nutrition goals and
dietary carbohydrates intakes over the season, so that lower intakes and
physique goals are the priority of training periods, whereas greater
carbohydrate intakes are allowed during competition preparation and
recovery to maximise glycogen stores.
Although total intake of carbohydrate is probably the most important
determinant of post-exercise refuelling, during periods of high volume
training, the distance athlete should use other dietary strategies to promote
recovery. Speedy intake of carbohydrate after exercise will maximise the
period of effective refuelling time (Burke et al., 2004). Carbohydrate-rich
foods in recovery snacks and meals should be chosen according to the need
to meet practical challenges (e.g. finding portable foods when the athlete is
“on the go”) or to meet additional nutritional goals (e.g. to provide a source of
iron, protein or other nutrient need). It is probably useful to co-ingest protein
with carbohydrate-rich recovery snacks. Although the effect of protein on
glycogen resynthesis is likely to be minimal in most circumstances (see
Tipton et al. 2007), various issues of recovery and adaptation require protein
synthesis. Indeed, in addition to refuelling, the distance athlete needs to
consider a range of recovery eating goals after training and races, including
rehydration (Shirreffs et al., 2007); repair and adaptation (Hawley et al.,
2007) and preserving the immune system (Nimmo et al., 2007)
Protein requirements during training
Data from studies of essentially recreational exercisers have led to the belief
that protein requirements are not altered by any form of physical activity.
However, the high volumes of training and the training intensities possible
only in elite athletes result in estimated protein requirements that are nearly
twice that of sedentary individuals; i.e. 1.6 – 1.7 g/kg/d (Tarnopolsky et al.
1988; Friedman & Lemon, 1989). Even for modestly trained individuals,
there is an increase in protein requirements estimated from nitrogen balance
experiments (Meredith et al., 1989; Phillips et al., 1993). Although no study
has specifically calculated protein requirements for elite female athletes,
nitrogen balance data imply that requirements for women are about 25 %
less than for men; i.e. 1.2 – 1.3 g/kg/d (Phillips et al. 1993; McKenzie et al.,
2000) Most athletes will achieve these protein intakes from an everyday diet
providing 10-15% of energy as protein and adequate energy. Nevertheless,
it is important to evaluate protein intake on a g/kg basis as opposed to a
percentage of the diet to avoid low intakes that can be seen in energy
restricting athletes. A low energy intake will also negatively affect protein
requirements (Calloway, 1975).
There are benefits to the timing of nutrient delivery, especially when
undertaking high volumes of training. When female athletes consumed a
nutritional supplement immediately after each workout during a training
camp, they achieved an improvement in nitrogen balance, lesser weight loss,
and improved performance on a trial completed at the end of the week than
when the supplement was consumed after breakfast (Roy et al., 2002).
Fuelling Up for Competition
Preparation for racing should ensure that muscle carbohydrate stores are
matched to the anticipated fuel needs of the event. For races of up to 60-90
minute duration, normalised muscle glycogen stores are adequate and can
generally be achieved by 24-36 h of high carbohydrate intake. Carbohydrate
loading in preparation for prolonged exercise resulted from pioneering
studies undertaken in the 1960s using percutaneous biopsy techniques to
examine fuel utilisation and enzyme activities in the muscle. These studies
on healthy but untrained men produced the classic 7-day model to
supercompensate muscle glycogen stores; a 3-4 day depletion phase of hard
training and low carbohydrate intake followed by a 3-4-day loading phase of
high carbohydrate intake and exercise taper (Bergstrom et al., 1967). Early
field studies of prolonged running events showed that this strategy enhanced
sport performance, not by allowing the athlete to run faster but by prolonging
the time that race pace could be maintained (Karlsson and Saltin, 1971).
A modified version of carbohydrate-loading was developed when well-trained
runners were shown to super-compensate their glycogen stores without a
severe depletion or glycogen stripping phase (Sherman et al., 1981). The
modified protocol, consisting simply of 3 d of high carbohydrate intake and
taper, was offered as a more practical competition preparation which avoided
the fatigue and complexity of the extreme diet and training requirements of
the previous depletion phase. More recently, muscle glycogen
concentrations were measured after 1 and 3 days of rest and a high
carbohydrate intake (10 g/kg body mass per day) in well-trained male
athletes (Bussau et al., 2002): this study found that optimal refuelling is
probably achieved within 36 to 48 h following the last exercise session, at
least when the athlete rests and consumes adequate carbohydrate.
Theoretically, carbohydrate loading can enhance performance in distance
races that would otherwise be limited by the fatigue caused by glycogen
depletion. Studies in well-trained runners have failed to detect benefits of
carbohydrate loading for 10 km treadmill running (Pitsiladis et al., 1996), a
20.9 km race on an indoor track (Sherman et al., 1981), and a 25 km
treadmill run (Sullo et al., 1998). By contrast, carbohydrate loading has been
shown to enhance performance of a 30 km cross country run (Karlsson and
Saltin, 1971), a 30 km treadmill run in trained men (Williams et al., 1992),
and a 25 km treadmill run in moderately trained men (Sullo et al., 1998).
Typically, carbohydrate loading is associated not with an increase in overall
running speed but with maintenance of race pace during the last part of the
run compared with the control trial or group. Therefore, runners and walkers
should consider carbohydrate loading for races of 30 km and longer.
Fat adaptation – a twist on depletion prior to carbohydrate loading
Distance runners and walkers should have a high capacity for fat oxidation
during exercise as a legacy of their training. However, this capacity can be
further up-regulated by as little as 5 d of training while following a low-
carbohydrate (<2.5 g/kg/d), high-fat (~65-70% of energy) diet. In trained
individuals, “fat adaptation” achieves a markedly increased fat oxidation and
reduced utilisation of muscle glycogen (“glycogen sparing”) during
subsequent sub-maximal exercise (Burke et al., 2000). This effect persists
even when followed by acute strategies to carbohydrate load, and eat
carbohydrate before and during the bout (for review see Burke and Kiens
2006). Such a combination of dietary strategies would seem the perfect
preparation for a marathon or distance walking event, simultaneously
optimising carbohydrate stores while maximising the capacity for fat
oxidation. Curiously, the effect on endurance and ultra-endurance
performance is unclear (Burke and Kiens, 2006).
There is now evidence that what was initially viewed as glycogen sparing
may be, in fact, a down-regulation of carbohydrate metabolism or “glycogen
impairment”. Fat adaptation/ carbohydrate restoration strategies are
associated with a reduction in the activity of a key enzyme regulating
carbohydrate metabolism, pyruvate dehydrogenase (Stellingwerff et al.,
2006). Such a change would impair rates of glycogenolysis at a time when
muscle carbohydrate requirements are high. This explains the observation
that when fat adaptation/carbohydrate restoration are applied to exercise
protocols which mimic a real-life race – self-pacing, and the interspersing of
high-intensity and moderate-intensity exercise - there is a compromised
ability to performance high-intensity sprints (Havemann et al. 2006) In many
endurance events, the critical activities in a race – the breakaway, the surge
up a hill, or the sprint to the finish line – are all dependent on the runner’s
ability to work at high intensities. With growing evidence that this critical
ability may be impaired, it now seems clear that fat adaptation or pre-loading
depletion strategies should not be undertaken by distance athletes.
Fluid and Fuel Intake during races
In distance running and walking events, especially road races, a network of
aid stations allows competitors to consume fluids during the race. In large
community participation events, a supply of water, sport drinks, and sponges
is provided, although elite competitors are usually provided with opportunities
to supply their own race beverages at specially marked tables. There is still
debate on the ideal hydration plans for distance events, with the observation
that most top runners are conservative with fluid intake while some of the
“back of the pack” participants in large community events risk serious
problems from over-consumption of fluids (Noakes, 2002; Almond et al.,
2005). These issues are covered in greater detail by Shirreffs et al. (2007).
The use of carbohydrate–electrolyte drinks (sport drinks) during races of 60
min or longer provides the runner or walker with the potential to replace fluid
and carbohydrate simultaneously, with the option of altering the carbohydrate
concentration of the drink (typically 4-8 g/100 ml), according to the priority of
rehydration or refuelling in a particular event. Sports gels and confectionery
are other easily consumed sources of carbohydrate often consumed by
distance athletes. There is good evidence of the benefits of carbohydrate
intake during prolonged (>90 min) exercise (Hargreaves 1999), with reports
dating back to the Boston marathon in the 1920s that the consumption of
sweets during the race prevented hypoglycaemia and enhanced running
performance (Gordon et al. 1925; Levine et al. 1924). Recent studies in
which carbohydrate ingestion enhanced a running protocol include a 40 km
outdoor run in the heat (Millard-Stafford et al. 1992), a 30 km road run
(Tsintzas et al. 1993), a marathon run on a treadmill (Tsintzas et al. 1995)
and a ~2 h treadmill protocol to exhaustion at 70% VO2max (Tsintzas et al.
1996b). The generally accepted mechanisms of performance enhancement
include prevention of hypoglycaemia, sparing of liver glycogen, and provision
of an additional muscle fuel substrate (Hargreaves 1999). However, in the
case of running, there is some evidence of muscle glycogen sparing, at least
in selected fibres (Tsintzas et al. 1996a; Tsintzas et al. 1993).
The effect of carbohydrate intake during shorter distance events is unclear
with the potential mechanism of any performance enhancements being
attributable to effects on the central nervous system rather than provision of
muscle fuel (see Burke, 2007). One study involving a 15 km treadmill run in a
hot environment found an improvement in speed over the last, self-paced
portion of the run when carbohydrate was ingested immediately before and
during the run compared with a placebo trial (Millard-Stafford et al. 1997). By
contrast, carbohydrate intake during an 18 km run failed to enhance
performance of a large group of runners or the fastest runners in the group
compared with water (van Nieuwenhoven et al. 2005), and highly trained
runners experienced a trivial effect on performance when carbohydrate was
consumed during a half-marathon (Burke et al., 2005. Further studies are
needed to determine the full range of events that might benefit from
carbohydrate intake immediately before and during the race.
Sex differences in nutrition strategies
It has been assumed that dietary advice for female distance athletes would
be a simple extrapolation from male athletes, scaled to their smaller size.
However, numerous studies have found that females oxidise more fat and
less carbohydrate than men during endurance exercise (see Tarnopolsky,
2000). An early study found that increasing dietary carbohydrate intake from
55% to 75% of habitual energy intake for 4 days neither increased glycogen
storage nor enhanced cycling performance in female athletes, in stark
contrast to the results seen in males (Tarnopolsky et al., 1995). Of course,
the relatively low energy intake of the females limited carbohydrate intake to
< 6.5 g/kg/d even in the “loading” phase. A follow-up study provided an
additional trial in which 75% of a higher energy intake achieved carbohydrate
intakes > 8 g/kg/d (Tarnopolsky et al., 2001). With higher carbohydrate and
extra energy, females increased muscle glycogen, albeit to levels which were
about 50% of the increase seen in male subjects. From a practical
perspective, carbohydrate loading is of use to female athletes only if they are
prepared to consume adequate energy and carbohydrate.
In contrast to the limited ability for women to carbohydrate load, the dietary
recommendations for men and women with respect to sport drink
consumption during exercise (Riddell et al., 2003; Wallis et al., 2006), and for
post-exercise glycogen re-synthesis (Tarnopolsky et al., 1997), appear to be
similar.
.
Sport Foods and Supplements
Many distance athletes, even at a recreational level, are consumers of sport
foods and supplements. Products such as sports drinks and liquid meal
supplements are specially designed to help a runner or walker meet specific
needs for energy, fluid and nutrients in situations where everyday foods are
not practical to eat, although the expense must be considered (see Burke,
2007). Nutritional ergogenic aids have generally been poorly tested or have
failed to live up to their claims when rigorous testing has been undertaken on
distance running/walking performance. The exception is caffeine, which may
enhance the performance of some runners (for review, see Graham, 2001).
Recent research has focused on the use of small doses of caffeine before
and during endurance exercise, since the benefits appear to be similar to that
achieved by larger doses of 6-9 mg/kg (see Maughan et al., 2007). Caffeine
intakes of as little as 3 mg/kg have been shown to enhance running
performance, including a worthwhile improvement of ~1% in an 8 km track
protocol (Bridge and Jones, 2006). However, runners who were provided
with very small amounts of caffeine (~ 1.3 mg/kg) during an 18 km road race
did not show a detectable improvement in performance (Van Nieuwenhoven
et al., 2005).
While bicarbonate supplementation is typically considered a strategy for
middle distance running (see Stellingwerff et al., 2007), it has been shown to
improve performance of the longer track events (e.g. 5,000 m races) (Oopik
et al., 2003; 2004). Creatine loading has become synonymous with the
enhancement of repeated sprint training or exercise bouts (see Tipton et al.,
2007) and is typically considered inappropriate for use by distance athletes.
In fact, runners recorded a slower time to complete a 6 km cross-country run
after creatine supplementation (Balsom et al, 1993), presumably due to the
accompanying increase in body mass. In spite of recent evidence that prior
creatine loading enhances the muscle’s capacity for glycogen loading or re-
synthesis (Nelson et al., 2001; van Loon et al., 2004), it is likely that the
increase in body mass would hinder performance in distance running events,
particularly if the course is hilly. Further research is needed to test the
hypothesis that glycerol hyperhydration can enhance thermoregulatory
function in conditions in which thermal stress limits running performance.
Finally, the claims made in support of the majority of other supplements and
compounds marketed as ergogenic aids are not supported by scientific
research (see Burke, 2007). Of course, more research is needed, using
rigorous control and carefully chosen protocols to test the claims for most
products. In many cases, particular (proposed) ergogenic compounds that
are used by distance athletes have not been appropriately tested and no
further comments can be made about these products. The reader is therefore
referred to the general conclusions provided by Maughan et al., 2007.
Summary of nutrition guidelines for distance athletes
Clear consensus
for Distance athletes should follow established
guidelines to meet the carbohydrate needs for their
training loads and to enhance recovery after each
training session. These strategies are particularly
important to promote performance and recovery for
key training sessions.
Distance athletes should consume sufficient
carbohydrate to prepare fuel stores that are
adequate for their event. Carbohydrate loading or
glycogen supercompensation will be of benefit to
longer events such as the marathon or 50 km walk.
A prolonged depletion phase is unnecessary and
may even impair performance.
Carbohydrate and fluid intake during an event is
possible and of probable value for races lasting
longer than 60 minutes. Each athlete should
experiment to find a plan that is practical and
provides benefits for their performance.
Iron deficiency may be a problem for some distance
runners, but this is a diagnosis of exclusion and
other causes need to be ruled out. Nutritional
counseling to increase intake of bioavailable iron is
an important goal of prevention and therapy.
Some sports supplements such as sports drinks and
liquid meals may be useful in providing a practical
way for distance athletes to meet their nutrition
goals. Moderate doses of caffeine can provide an
ergogenic benefit to distance running and may be
useful for some runners.
Clear consensus
against Distance athletes should not practise extreme levels
of energy restriction to achieve loss of body
weight/body fat without considering the effect on
their ability to meet goals for carbohydrate, protein,
iron or other nutrients. Hormonal balance, bone
health and the immune system are also critically
impaired by inadequate energy intakes.
Routine supplementation with iron or iron injections
in the belief that it enhances performance should be
strongly discouraged in the absence of documented
iron depletion or anaemia. Supplementation in the
absence of deficiency can lead to serious medical
conditions such as haemosiderosis.
The majority of supplements that are promoted to
distance athletes are unlikely to provide substantial
benefits, and should not replace sound eating and
training practices.
Issues that are
equivocal It is unclear whether distance athletes will enhance
adaptations and performance outcomes by
undertaking deliberate strategies to restrict
carbohydrate availability during training. In the real
world, elite athletes will probably achieve some level
of periodisation of carbohydrate status within the
microcycles of their training program. Any benefits
of more prolonged carbohydrate depletion need to
be balanced by the possible disadvantages.
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... It is not clear if this is due to fewer symptoms which leads to an increase in intake. In addition, there was no difference between genders [28,[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58]. ...
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