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Swimming
Chapter 46
Swimming
RICK L. SHARP
Introduction
Competitive swimming is a sport practised
worldwide and includes swimming events of
varied distances (50–1500 m, 22 s to 16 min) and
stroke styles (freestyle or crawl stroke, backstroke, breaststroke and butterfly). Competitive
swimming meets are held year-round and the
age range of the swimmers is between 6 and 80
years. In the United States alone there are
between 1.0 and 1.5 million competitive swimmers affiliated with community club teams, high
school teams, college teams, and masters
swimming teams (M.L. Unger, personal
communication).
Each swimming practice session can last up to
about 3 h and may include a total swimming
volume of 10 000 metres or yards. During this
time, swimmers are engaged in various types of
training that include long-distance endurance
training, interval training, sprint training, and
stroke instruction. The specific stroke styles
swum during training depend on the athlete’s
specialty, but most swimmers swim at least 75%
of their total training volume in freestyle. This
training is frequently done twice per day and 6
days per week. In addition to this, many swimmers also participate in dry land training such
as strength training or supplemental endurance
running or cycling. Thus, the nutritional
demands of training in this sport can be quite
extraordinary.
Energy demands of
swimming training
The large volume of intensive training of these
athletes imposes a tremendous demand on
energy supply. Sherman and Maglischo (1992)
have estimated the energy requirement of
swimming training at approximately 16.8–
22.6 MJ · day–1 (4000–5400 kcal · day–1) for males
working 4 h · day–1 and between 14.2 and
16.8 MJ · day–1 (3400–4000 kcal · day–1) for females
working 4 h · day–1. Certainly, these values will
vary considerably according to such factors
as the intensity of the exercises used, the
swimmer’s body mass, and mechanical efficiency. Nevertheless, these high energy needs
can be difficult for swimmers to meet.
Several studies have examined the daily diets
of competitive swimmers to determine if energy
needs are being met. Van Handel et al. (1984)
used diet records to examine the energy intakes
of 14 female and 13 male competitive swimmers
who had competed in the US National Championhips and were preparing for the Olympic
Trials. Their findings indicate that the energy
intake of the men averaged 18.2 MJ · day–1
(4350 kcal · day–1), with a range between 12.6 and
28.6 MJ · day–1 (3010–6830 kcal · day–1). Expressed
relative to body weight, these men were consuming an average of 0.22 MJ · kg–1 (50 kcal · kg–1). The
women had energy intakes averaging 9.6 MJ ·
day–1 (2300 kcal · day–1), with a range between
6.3 and 13.8 MJ · day–1 (1500–3300 kcal · day–1).
Relative to body weight, these women consumed
609
610
sport-specific nutrition
an average of 0.15 MJ · kg–1 (36 kcal · kg–1). Distribution of energy for these athletes was 49%
of energy from carbohydrate and 34% of energy
from fat for the men, while the women reported
53% of energy from carbohydrate and 30% of
energy from fat.
Berning et al. (1991) reported energy intakes
of adolescent developmental level swimmers
attending a training camp. Males consumed an
average of 21.9 MJ · day–1 (5230 kcal · day–1) while
females reported 15.0 MJ · day–1 (3580 kcal ·
day–1). Distribution of energy among the energy
macronutrients was not different from the
general population, prompting the authors to
conclude that these swimmers consumed too
much fat and inadequate carbohydrate.
In an attempt to determine the influence of
training volume on the energy intake of competitive swimmers, Barr and Costill (1992) examined
diet records of 24 males during a period of ‘low
volume’ training (22 km · week–1) and during
‘high volume’ training (44 km · week–1). Energy
intake averaged 15.3 MJ · day–1 (3650 kcal · day–1)
during the lower volume training and increased
significantly to 17.7 MJ · day–1 (4230 kcal · day–1)
during the 6 weeks of high-volume training. It
was noted that this increase in energy intake did
not fully compensate for the higher energy
demand of the longer training, since the swimmers maintained their body weight while they
lost subcutaneous fat.
Costill et al. (1988a) examined male collegiate
swimmers before, during and after 10 days of
increasing training. Their training distance was
increased from 4266 to 8970 m · day–1 while
average intensity was maintained at 94% of their
maximum oxygen uptake. This resulted in an
average energy cost during training of 9.6 MJ ·
day–1 (2300 kcal · day–1). It was noted that four of
the 12 swimmers could not tolerate the higher
training volume and were forced to swim their
training bouts at slower speeds. In addition,
these swimmers had reduced muscle glycogen
concentration as a consequence of the combined
effect of the intensified training and their low
carbohydrate intakes. These findings led the
authors to conclude that some swimmers have
difficulty in meeting the energy demands of
high-volume training and experience chronic
muscle fatigue as a result of their failure to ingest
sufficient carbohydrate to match the energy
demands.
The studies reviewed above suggest that
male competitive swimmers in the age range of
16–23 years typically ingest approximately
18.0 MJ · day–1 (4300 kcal · day–1), while females
consume only about 10.9 MJ · day–1 (2600 kcal ·
day–1) despite the fact that female and male
swimmers perform similar training volume and
intensity. When these data are compared with the
estimated energy requirements of swimming
training proposed by Sherman and Maglischo
(1992), males tend to remain in energy balance
(18.0 MJ · day–1 average intake vs. 16.8–22.6 MJ ·
day–1 (4300 vs. 5400 kcal · day–1) estimated
requirement) while female swimmers tend to
maintain a negative energy balance (10.9 MJ ·
day–1 average intake vs. 14.2–16.8 MJ · day–1 (2600
vs. 3400–4000 kcal · day–1) estimated requirement). These data illustrate the nutritional
dilemma facing competitive swimmers, especially females, and their coaches. The tremendous training demands imposed on these
athletes require careful consideration of the
swimmer’s diet to make sure that adequate
amounts of food are eaten to provide the energy,
macronutrients and micronutrients necessary to
support the enormous training loads.
Body composition
With such high energy demands of daily training
in competitive swimming, one might wonder
why body fat percentages of swimmers are not
lower than they are. Typically, male competitive
swimmers have body fat percentages in the
range of 8–15% and females at 15–22%. Indeed,
studies have confirmed that body composition of
competitive swimmers is usually about 4–6%
greater than age- and ability-matched endurance
runners (Novak et al. 1977; Thorland et al. 1983).
There are a number of possible explanations
for the tendency of swimmers to carry more fat
than runners despite similar training loads. One
swimming
explanation is that although running tends to
have a somewhat anorexic effect, especially in
the few hours after exercise, swimming may
have an opposite effect by stimulating appetite
(Harri & Kuusela 1986). This would imply that
swimmers tend to increase their energy consumption in parallel with their training where
runners may not. To this author’s knowledge,
there have been no published studies comparing
the effects of running and swimming on the
postexercise appetite. Under this assumption
of increased appetite in swimmers, swimmers
would not be expected to lose a great deal of
body fat during their training. A study by
Johnson et al. (1989) with female university
swimmers supports this argument since no
changes in body composition were observed
over a 25-week season of training. In contrast,
however, Barr et al. (1991) reported decreased
body fat, increased lean body mass, and no
change in body weight in male college swimmers
training 22 000 m · week–1 during a 25-week
season. In agreement with this study showing
changing body composition in males during
swim training is a study by Meleski and Malina
(1985) showing decreased body weight,
decreased absolute and relative fat mass, and
increased lean body mass in a group of female
college swimmers during the first 2 months of a
training season.
Fig. 46.1 Swimmers favour high
training volumes. This means that
a high energy intake is essential,
but opportunities for eating may
be limited when long training
sessions must be combined with
work or study. Photo © Allsport.
611
Another explanation that has been proposed
for the higher body fat percentages in competitive swimmers is a possible difference in fuel utilization both during and following the exercise
that promotes fat storage in swimmers. As
support for this argument, some have pointed to
studies of cold exposure which is known to
stimulate fat storage both in animal models and
in humans. To determine if swimming training
alters fuel utilization and the hormonal milieu
differently from running, Flynn et al. (1990)
monitored energy expenditure and fuel utilization of eight male swimmers and runners while
exercising at 75% of maximum oxygen uptake
and during 2 h of recovery. Although the energy
cost of recovery was similar between the two
exercise modes, the respiratory exchange ratio
results suggested increased fat oxidation after
swimming compared with running. In contrast,
serum glycerol concentration was elevated to a
greater extent after running than after swimming, suggesting enhanced mobilization of
triglycerides with running. Whether this different response can account for the differences in
body composition between runners and swimmers remains to be studied.
Carbohydrate needs in training
The high volume and intensity of swimming
sport-specific nutrition
training places a great demand not only on
dietary energy, but also on the carbohydrate
needs of these athletes. Maglischo (1993) has estimated that dietary carbohydrate needs of swimmers range between 500 and 800 g · day–1. Thus,
a swimmer who consumes a diet providing
16.8 MJ · day–1 (4300 kcal · day–1) with 50% of the
energy from carbohydrate will be consuming
approximately 500 g · day–1 of carbohydrate and
therefore may not meet the carbohydrate
demand of the daily training. Clearly, these athletes should make carbohydrate intake a priority
in their daily diet.
To determine the amount of muscle glycogen
depletion that can occur during typical swim
training bouts, Costill et al. (1988b) examined
muscle glycogen levels of male collegiate swimmers before and after swimming either 2743 or
5486 m. Each swimmer performed the 5486 m of
training twice; once by doing 60 ¥ 91.4 m swims
and once by performing 12 ¥ 457.2 m swims.
Biopsies were taken from the anterior deltoid
before, at the half-way point of the training
session (2743 m), and at the end of each training
session and analysed for glycogen concentration.
Additional biopsies were taken after 8 h of recovery and ingestion of 112 g carbohydrate to assess
the amount of glycogen repletion that might
occur in this amount of time. When the training
sessions were performed with repeated 91.4-m
swims, muscle glycogen concentration declined
by 68% at 2743 m, and by 87% at 5486 m (Fig.
46.2). Using repeated 457.2-m swims, muscle
glycogen declined by 54% at 2743 m, and by 63%
at 5486 m. The greater amount of glycogen depletion with 91.4-m repeats than with 457.2-m
repeats was accounted for by a significantly
faster swimming speed during the 91.4-m
repeats (ª 7% faster than during the 457.2-m
repeats). In recovery, glycogen repletion was 52%
complete after 8 h and ingestion of 112 g of
carbohydrate.
These findings show the large loss of muscle
glycogen that can occur during a single training
session among competitive swimmers. When
one considers that many swimmers perform this
kind of training on a daily basis, and in many
140
120
100
Muscle glycogen (mmol.kg–1)
612
80
60
40
20
0
Pre-exercise
2743
5486
Distance per interval set (m)
Fig. 46.2 Muscle glycogen utilization during 2743- and
5486-m interval swim training using repeated 91.4-m
( ) or 457-m ( ) swims. Adapted from Costill et al.
(1988b).
instances twice per day, the probability of
chronic glycogen depletion is great, especially
considering the incomplete glycogen repletion in
the 8 h of recovery. Chronic glycogen depletion
may then result in poor performances in subsequent training sessions and in competitions that
may follow a period of such training. An obvious
solution to this problem is to train only once
per day and consume a diet containing at least
500 g · day–1 of carbohydrate. Less frequent training would likely not deplete glycogen from
working muscles as much as twice per day training, and the higher intake of dietary carbohydrate would tend to accelerate glycogen
repletion in the 24 h between training sessions,
especially if a large quantity of carbohydrate is
ingested during the first 2 h after the training is
finished (MacDougall et al. 1977; Ivy et al. 1988).
swimming
Lamb et al. (1990) tested whether a diet in
which 80% of calories came from carbohydrate
was superior to a 43% carbohydrate diet in supporting the daily training of collegiate swimmers. Both diets provided 19.6 MJ · day–1 (4680
kcal · day–1) and were maintained for 9 days.
During the last 5 days of each diet, swimmers
performed intervals of various distances ranging
from 50 m up to 3000 m and mean swim velocities
were recorded. These authors found no significant differences between the two diets in performance of the interval sets. However, they did
note that the swimmers who regularly consumed
a high carbohydrate diet tended to perform
better than those who generally consumed a low
carbohydrate diet. A possible reason for the lack
of difference in performance between the high
and moderate carbohydrate diets could be that
even in the moderate carbohydrate diet, enough
carbohydrate was supplied to support the
demands of their training. At 19.6 MJ · day–1 (4680
kcal · day–1) and 43% carbohydrate, these subjects
were consuming an average of 503 g carbohydrate · day–1. Costill and Miller (1980) reported
that muscle glycogen repletion is proportional to
the mass of carbohydrate consumed until carbohydrate intake reaches approximately 600 g ·
day–1. Therefore, it is possible that the 935 g of
carbohydrate that were provided in the 80% carbohydrate diet did not stimulate any greater rate
of glycogen repletion than the 503 g of carbohydrate provided in the 43% carbohydrate diet.
In light of the observations of Costill et al.
(1988a), wherein four of the 12 swimmers
studied failed to eat enough carbohydrate to
prevent chronic muscle glycogen depletion
during 8970 m · day–1 training, it would seem
prudent to recommend that swimmers consume
a diet that (i) meets the energy requirements of
training and (ii) provides at least 600 g carbohydrate · day–1.
Carbohydrate ingestion during
training sessions
A number of studies have shown improved
endurance performance when carbohydrate is
613
ingested at frequent intervals during the exercise
(Coyle et al. 1983, 1986; Coggan & Coyle 1987;
Davis et al. 1988; Tsintzas et al. 1993). Typically,
the exercise modes studied in these investigations have been either cycling or running. The
hypothesized benefit of carbohydrate ingestion
is improved maintenance of blood glucose
throughout the duration of the activity and/or
muscle glycogen sparing leading to increased
carbohydrate availability at a time when the low
endogenous carbohydrate supplies generally
limit muscular performance.
To determine if carbohydrate ingestion during
exercise would have similar beneficial effects on
the performance of swimming training bouts,
O’Sullivan et al. (1994) measured swimming
performances during a standardized training
session once while ingesting a placebo and once
while ingesting a liquid carbohydrate supplement. In each of these trials, the nine male collegiate swimmers performed a 5944-m training
session composed of a mixture of low- and highintensity interval training bouts. The final 914 m
of the training session was 10 ¥ 91.4 m swims
with 20 s rest between each as a performance
trial. Performance was measured as each
swimmer’s average velocity during the first 5,
second 5, and for the whole set of 10 ¥ 91.4 m.
During the carbohydrate supplementation trial,
the swimmers were given 1 g · kg–1 of glucose
polymers in 50% solution 10 min into the training
session, and 0.6 g · kg–1 of glucose polymers in
20% solution every 20 min thereafter according
to the feeding schedule of Coggan and Coyle
(1988). The placebo trial was the same as the
carbohydrate trial, but an artificially sweetened
placebo drink was substituted for the carbohydrate drink. The trials were conducted 7 days
apart in a randomized, double-blind manner.
Blood samples were taken before the training
session, immediately before each feeding, and at
the conclusion of the 10 ¥ 91.4 m performance
trial. During the placebo trial, blood glucose concentration remained fairly stable throughout the
first 100 min of the training but rose significantly
during the 10 ¥ 91.4 m performance test to a final
level of 6.3 mmol · l–1 (Fig. 46.3). In the carbohy-
614
sport-specific nutrition
drate feeding trial, blood glucose concentration
was slightly elevated over the placebo trial at all
time points, but no significant differences were
observed. Performance times for the 10 ¥ 91.4 m
training set at the end of training averaged 59.1 s
in the placebo trial and 59.9 s during the carbohydrate trial. The authors concluded that carbohydrate supplementation was not effective in
improving performance late in a swimming
practice because blood glucose remains stable
even without supplemental carbohydrate.
However, individual differences in their responses were presented. Two of the subjects did
Blood glucose (mM)
7
6
5
4
4846 m swim
Perf.
3
0
20
40
60
80
100
120
Time (min)
Fig. 46.3 Blood glucose concentration throughout a
5486-m swim training session when fed placebo (䊊) or
carbohydrate (䊉) every 20 min. Perf., performance trial
of 10 ¥ 91.4-m swims. Adapted from O’Sullivan et al.
(1994).
experience a substantial decline in blood glucose
concentration during the training in the placebo
trial. During his placebo trial, one swimmer’s
blood glucose concentration dropped from
4.3 mmol · l–1 before the training to a low of 2.6
mmol · l–1 immediately before the 10 ¥ 91.4 m performance trial (Table 46.1). The ingestion of carbohydrate completely prevented this decline and
his performance time improved by 1.3 s from
64.3 s in the placebo trial to 63.0 s in the carbohydrate trial. Another subject experienced a drop in
blood glucose concentration from 5.6 mmol · l–1
pre-exercise to 3.7 mmol · l–1 immediately before
the performance trial. Again, the carbohydrate
supplementation prevented this decline and performance improved by 1.1 s from 58.4 to 57.3 s.
Thus, it seems that the carbohydrate supplementation protocol used in this study is effective in
improving late-practice performance but only
for those individuals who normally experience
declining blood glucose concentration during
the training.
Because it would be impossible for swimmers
to know if they normally experience declining
blood glucose concentration during training
without taking blood samples, coaches may
want to recommend carbohydrate supplementation for the entire team. In those individuals who
are able to maintain their blood glucose concentrations without supplemental carbohydrate,
there is little, if any, risk in consuming the carbohydrate. Therefore, supplementing the entire
team would be one way of assuring that those
swimmers who need the extra carbohydrate
would get it. Alternatively, coaches could watch
their swimmers for signs of excessive muscle
Table 46.1 Responses of two subjects who had declining blood glucose concentration during placebo and
carbohydrate trials. Adapted from O’Sullivan et al. (1994).
Trial
Pre-exercise
(mmol · l-1)
Preperformance
(mmol · l-1)
Time/91.4 m (s)
Subject 1
Placebo
Carbohydrate
4.3
4.5
2.6
4.3
64.3
63.0
Subject 2
Placebo
Carbohydrate
5.6
5.7
3.7
7.2
58.4
57.3
swimming
fatigue during the latter part of training sessions
and prescribe a carbohydrate supplement only to
those who consistently seem to have difficulty
maintaining their work output.
There is a more fundamental question than
whether or not carbohydrate supplementation is
effective in improving training performance. By
preventing the decline in blood glucose concentration during training, we effectively eliminate
one of the physiological/metabolic stresses
imposed by the training. Since training is a
careful dosage of physical stress to create longterm adaptations that will ultimately improve
competitive performance potential, elimination
of these stresses may lessen the degree of adaptation experienced by the athlete. Whether or not
one adapts in a performance-enhancing way to
low carbohydrate availability is not currently
known, but this may be part of the stimulus that
improves glycogen storage in endurance athletes
(Gollnick et al. 1973; Piehl et al. 1974; Costill et al.
1985a).
Carbohydrate ingestion after training
Studies have shown that muscle glycogen resynthesis is accelerated when carbohydrate is
ingested within 1–2 h after the exercise is stopped
(Ivy et al. 1988). In this immediate postexercise
period, evidence suggests that high glycaemic
index sugars may be the preferred carbohydrate
source since insulin is known to be a potent
activator of muscle glycogen synthase. A recent
study also suggests including some protein in
the postexercise meal because the protein will
augment the insulin response to the carbohydrate and thereby stimulate an even greater rate
of muscle glycogen storage (Zawadzki et al.
1992). Since competitive swimmers likely experience large decrements in muscle glycogen
concentration during single training sessions, it
seems wise to provide a carbohydrate source
soon after the training session ends. This strategy
may be helpful in preventing the chronic muscle
glycogen depletion that undoubtedly occurs in
many swimmers, especially those training twice
per day.
615
Chronic muscle glycogen depletion
and overtraining
With all the training competitive swimmers do, it
is not surprising that overtraining has become
almost an epidemic in swimming. The frequent,
high-volume, and high-intensity training these
athletes perform often results in a chronic muscle
fatigue that, if unchecked, may lead to the development of an overtraining state. Chronic muscle
fatigue has been linked to failure to adequately
replace the muscle glycogen stores between
training sessions due to the combination of
heavy training and inadequate dietary carbohydrate intake. Since a competitive swimming
season may last as long as 25 weeks before a
break from training is taken, swimmers can
suffer from chronic depletion for up to 6 months.
At the end of most swimming seasons, swimmers gradually reduce both the volume and
intensity of training in preparation for their
season-ending competition. This ‘taper period’
has not been studied extensively, but the few
studies that have been done indicate that
improved strength or power and increased
muscle glycogen stores may be partly responsible for the enhanced performance that typically
occurs with the taper.
Protein requirements during
swimming training
The prior discussion concerning carbohydrate
needs of competitive swimmers suggests that
many swimmers may experience chronic muscle
glycogen depletion during their daily training.
Lemon and Mullin (1980) have shown that
protein catabolism is accelerated when exercising while glycogen depleted. Therefore, competitive swimming training may often result in
increased protein catabolism that needs to be
compensated for with extra dietary protein
intake. Furthermore, the relatively low energy
intake that has been reported for some swimmers
may also trigger an increase in protein
catabolism.
Lean body mass has been shown to signifi-
616
sport-specific nutrition
cantly correlate with swimmers’ performance in
a 91.4-m freestyle (Stager et al. 1984). In addition,
numerous studies have shown the importance of
muscle strength and power in performance of
competitive swimming (Sharp et al. 1982; Costill
et al. 1985b, 1986; Sharp 1986; Cavanaugh &
Musch 1989). Thus, development and maintenance of lean mass to preserve muscle strength
and power should be a priority for competitive
swimmers. Unfortunately, this seems to be a difficult task during the heavy training phase of
their season as studies have shown decrements
in muscle power despite continued resistance
training during midseason (Sharp 1986;
Cavanaugh & Musch 1989) followed by
increased power during the taper phase of training (Costill et al. 1985b). Whether these changes
in muscle power are related to a chronic increase
in muscle protein catabolism followed by an
attenuation of muscle wasting during the taper
phase has not been studied.
There are other studies which provide indirect
evidence of an enhanced protein need during
swimming training. Kirwan et al. (1988) and
Morgan et al. (1988) showed evidence of muscle
damage with a twofold increase in serum creatine kinase activity and increased muscle soreness in male college swimmers when training
volume was increased from 4266 m · day–1 to
8970 m · day–1. In another study on the effects of
swimming training on protein catabolism,
Lemon et al. (1989) observed an increase in serum
urea concentration and urinary urea excretion
after a 4572-m training session in competitive
swimmers. Conversely, Mussini et al. (1985)
found no evidence of increased muscle proteolysis using postexercise urinary 3-methyl-histidine
excretion in a group of 16–20-year-old males performing a 2000-m competitive swimming training session. It should be noted, however, that the
training volume used in this study was considerably less than that used in the previous studies
and less than that typically used by most
competitive swimmers.
Although the United States recommended
daily allowance (RDA) for protein is set at
0.8 g · kg–1 for adults, Friedman and Lemon (1989)
suggest that a protein intake of approximately
1.5 g · kg–1 may be more appropriate to support endurance exercise training. In addition,
Marable et al. (1979) recommend a protein intake
up to 2–3 g · kg–1 to support the muscle building
requirements of resistance training. Since competitive swimming training employs considerable involvement in both endurance and
resistance training, their protein needs may
lie somewhere within this range of about
1.5–2 g · kg–1 · day–1. The typical young-adult
female competitive swimmer in the Netherlands
consumes approximately 50–60 g protein · day–1,
translating to about a protein intake of 0.9–
1.2 g · kg–1 · day–1 (van Erp-Baart et al. 1989).
These authors also report the typical protein
intake of male swimmers in the range of 80–
100 g · day–1, or a protein intake of about 1.1–
1.3 g · kg–1 · day–1.
Perhaps if swimmers maintained a higher
protein intake and a higher carbohydrate intake,
and consumed enough calories to match the
energy demands of their training, responses such
as loss of muscle power in the middle of the
season, chronic muscle fatigue, overtraining, and
recovery of power and performance ability
during taper would be lessened. Elimination
of these responses might be expected to result
in improved performance of these athletes
throughout their competitive season, instead
of only at the end of a taper period. However,
many coaches worry that the large performance
improvement usually observed with the seasonending taper would no longer occur if the swimmers were not pushed to the edge of overtraining
throughout the early and midseason phases.
In addition, they often fear that physiological
capacities such as aerobic endurance and anaerobic power will not be fully developed in their
athletes if training volume is reduced. Consequently, training for competitive swimming will
likely continue to place extraordinary demands
on the young athletes who choose this as their
sport.
swimming
Micronutrient requirements in
competitive swimming
The only vitamin or mineral that has received
much attention in the literature on dietary habits
of competitive swimmers is iron. Perhaps the
reason for this is that swimmers tend to consume
a large amount of food and typically exceed the
RDA for most of the nutrients. However, there is
evidence of iron deficiency, particularly among
female swimmers, even when RDA is met.
Brigham et al. (1993) determined iron status in
25 female college swimmers on a biweekly basis
throughout a 25-week competitive season. In
addition, they examined the effectiveness of iron
supplementation during this season. Before
breaking the swimmers into an experimental
(iron supplement) and placebo group, these
authors observed that 17 of the swimmers had
depleted iron stores (defined as serum ferritin
concentration < 12 mg · l–1) while five of the swimmers were defined as anaemic (haemoglobin
< 12 g · dl–1). During the 5 weeks in which the
experimental group received 39 mg elemental
iron as an iron supplement per day, haemoglobin
concentration increased in 24% of the subjects
and plasma ferritin concentration increased in
68% of the subjects. In the control group who did
not ingest an iron supplement, haemoglobin concentration decreased despite consuming a diet
containing 16.3 mg iron · day–1. These authors
concluded that moderate iron supplementation
is effective in preventing a decline in iron status
during swimming training but a higher dose
may be needed to reverse a pre-existing iron
deficiency.
Ganzit et al. (1993; cited in Burke 1993) tested
the effectiveness of 80 mg iron supplementation
per day in male and female swimmers. Swimmers in the experimental group maintained their
plasma ferritin levels while those swimmers in
the placebo group experienced a decrease in
plasma ferritin concentration. These authors
also noted an improvement in anaerobic capacity
and reduced lactic acid response to submaximal
exercise that was more marked in the experimental group than in the placebo group. In the
617
females, these improvements were confined
only to the group that received the dietary iron
supplement. Since haemoglobin concentrations
did not change in either of the groups, these
authors concluded that performance gains were
made at the level of iron-associated muscle
enzymes.
Walsh and McNaughton (1989) studied the
effects of 150 mg iron supplementation per day
.
on the haematology and Vo2max. of competitive
female swimmers training at least 2 h · day–1 and
7 days a week. During this period, the experimental group had an increase in haemoglobin
concentration from 12.5 g · dl–1 before supplementation to 13.6 g · dl–1 after supplementation
with no change in the placebo group. Plasma ferritin concentration dropped in the placebo group
from 28 to 16 mg · l–1 while no signficant change
was observed in the experimental group (26 to
21 mg · l–1). By the end of the study, 40% of the subjects in the placebo group were classified as iron
deficient (serum ferritin £ 12 mg · l–1, haemoglobin
≥ 12 g · dl–1) and 10% of the subjects were classified as anaemic (serum ferritin £ 12 mg · l–1,
haemoglobin £ 12 g · dl–1). These data are shown
in Fig. 46.4. None of the swimmers who received
the iron supplement was classified as either
iron deficient or anaemic. These authors concluded that young female swimmers should be
routinely tested for iron status and that iron
supplementation undertaken when deemed
necessary.
Conclusion
The nutritional problems that have been summarized in this chapter may all be linked to the
volume, frequency and intensity of training these
athletes perform. Thus, the difficulties in trying
to meet the energy demands, supply adequate
carbohydrate to fuel the exercise and aid recovery, minimize muscle proteolysis, and prevent
iron depletion and the associated negative effects
on haematology could be avoided most simply
by reducing training. At the very least, swimming coaches should design training programmes that lessen the risk of developing the
618
sport-specific nutrition
Serum iron (µg.dl–1)
95
educating swimmers and their parents about
general nutritional principles and specific nutritional problems of their sport are all ways swimming coaches can help assure that nutrition
supports the efforts of these dedicated athletes
instead of limiting their performance.
90
85
80
75
70
65
(a)
0
12
Ferritin (µg.l–1)
28
24
20
16
(b)
0
12
0
12
RBC (103.ml–1)
4800
4600
4400
(c)
Haemoglobin (g.dl–1)
14
13
12
(d)
0
12
Time (weeks)
Fig. 46.4 Iron status and haematology of female
competitive swimmers taking either placebo (䊊) or
150 mg iron supplement (䊉) daily during 12 weeks of
swim training. Adapted from Walsh and McNaughton
(1989).
nutritional problems outlined in this chapter.
Alternating between high and lower volume
training days, allowing adequate time between
intense practices for muscle glycogen recovery,
References
Barr, S.I. & Costill, D.L. (1992) Effect of increased training volume on nutrient intake of male collegiate
swimmers. International Journal of Sports Medicine 13,
47–51.
Barr, S.I., Costill, D.L., Fink, W.J. & Thomas, R. (1991)
Effect of increased training volume on blood lipids
and lipoproteins in male collegiate swimmers.
Medicine and Science in Sports and Exercise 23, 795–800.
Berning, J.R., Troup, J.P., Van Handel, P.J., Daniels, J. &
Daniels, N. (1991) The nutritional habits of young
adolescent swimmers. International Journal of Sport
Nutrition 1, 240–248.
Brigham, D.E., Beard, J.L., Krimmel, R.S. & Kenney,
W.L. (1993) Changes in iron status during competitive season in female collegiate swimmers. Nutrition
9, 418–422.
Burke, L.M. & Read, R.S.D. (1993) Dietary supplements
in sport. Sports Medicine 15, 43–65.
Cavanaugh, D.J. & Musch, K.I. (1989) Arm and leg
power of elite swimmers increase after taper as measured by Biokinetic variable resistance machines.
Journal of Swimming Research 5, 7–10.
Coggan, A.R. & Coyle, E.F. (1987) Reversal of fatigue
during prolonged exercise by carbohydrate infusion or ingestion. Journal of Applied Physiology 63,
2388–2395.
Coggan, A.R. & Coyle, E.F. (1988) Effect of carbohydrate feedings during high-intensity exercise. Journal
of Applied Physiology 65, 1703–1709.
Costill, D.L. & Miller, J.M. (1980) Nutrition for
endurance sport: carbohydrate and fluid balance.
International Journal of Sports Medicine 1, 2–14.
Costill, D.L., Fink, W.J., Hargreaves, M., King, D.S. &
Thomas, R. (1985a) Metabolic characteristics of
skeletal muscle during detraining from competitive
swimming. Medicine and Science in Sports and Exercise
17, 339–343.
Costill, D.L., King, D.S., Thomas, R. & Hargreaves, M.
(1985b) Effects of reduced training on muscular
power in swimmers. Physician and Sportsmedicine 13,
94–101.
Costill, D.L., Rayfield, R., Kirwan, J. & Thomas, R.
(1986) A computer based system for the measurement of force and power during front crawl swimming. Journal of Swimming Research 2, 16–19.
swimming
Costill, D.L., Flynn, M.G., Kirwan, J.P. et al. (1988a)
Effects of repeated days of intensified training on
muscle glycogen and swimming performance. Medicine and Science in Sports and Exercise 20, 249–254.
Costill, D.L., Hinrichs, D., Fink, W.J. & Hoopes, D.
(1988b) Muscle glycogen depletion during swimming interval training. Journal of Swimming Research
4, 15–18.
Coyle, E.F., Hagberg, J.M., Hurley, B.F., Martin, W.H.,
Ehsani, A.A. & Hollszy, J.O. (1983) Carbohydrate
feeding during prolonged strenuous exercise can
delay fatigue. Journal of Applied Physiology 55,
230–235.
Coyle, E.F., Coggan, A.R., Hemmert, M.K. & Ivy, J.L.
(1986) Muscle glycogen utilization during prolonged
exercise when fed carbohydrate. Journal of Applied
Physiology 61, 165–172.
Davis, J.M., Lamb, D.R., Pate, R.R., Slentz, C.A.,
Burgess, W.A. & Bartoli, W.P. (1988) Carbohydrate–
electrolyte drinks: effects on endurance cycling in
the heat. American Journal of Clinical Nutrition 48,
1023–1030.
Flynn, M.G., Costill, D.L., Kirwan, J.P. et al. (1990) Fat
storage in athletes: metabolic and hormonal
responses to swimming and running. International
Journal of Sports Medicine 11, 433–440.
Friedman, J.E. & Lemon, P.W. (1989) Effect of chronic
endurance exercise on retention of dietary protein.
International Journal of Sports Medicine 10, 118–123.
Ganzit, G.P., Giribaudo, C.G. & Biancotti, P.P. (1989)
Effetti della somministrazione di supplemento di
ferro ferritinico sull’ adaltamento funzionale
aerobico e anaerobico all’ alienamento, in nuotatori
maschi e femmine. Medicina dello Sport 42, 7–15.
Gollnick, P.D., Armstrong, R.B., Saltin, B., Saubert,
C.W., Sembrowich, W.L. & Shepherd, R.J. (1973)
Effects of training on enzyme activity and fiber composition of human skeletal muscle. Journal of Applied
Physiology 34, 107–111.
Harri, M. & Kuusela, P. (1986) Is swimming exercise or
cold exposure for rats? Acta Physiologica Scandinavica
126, 189–197.
Ivy, J.L., Katz, A., Cutler, C.L., Sherman, W.M. & Coyle,
E.F. (1988) Muscle glycogen synthesis after exercise:
effect of time of carbohydrate ingestion. Journal of
Applied Physiology 64, 1480–1485.
Johnson, G.O., Nebelsick-Gullett, L.J., Thorland, W.G.
& Housh, T.J. (1989) The effect of a competitive
season on the body composition of university female
athletes. Journal of Sports Medicine and Physical Fitness
29, 314–320.
Kirwan, J.P., Costill, D.L., Flynn, M.G. et al. (1988)
Physiological responses to successive days of intense
training in competitive swimmers. Medicine and
Science in Sports and Exercise 3, 255–259.
Lamb, D.R., Rinehardt, K.F., Bartels, R.L., Sherman,
619
W.M. & Snook, J.T. (1990) Dietary carbohydrate and
intensity of interval swim training. American Journal
of Clinical Nutrition 52, 1058–1063.
Lemon, P.W. & Mullin, J.P. (1980) Effect of initial muscle
glycogen levels on protein catabolism during exercise. Journal of Applied Physiology 48, 624–629.
Lemon, P.W., Deutsch, D.T. & Payne, W.R. (1989) Urea
production during prolonged swimming. Journal of
Sports Science 7, 241–246.
MacDougall, J.D., Ward, G.R., Sale, D.G. & Sutton, J.R.
(1977) Muscle glycogen repletion after high-intensity
intermittent exercise. Journal of Applied Physiology 42,
129–132.
Maglischo, E.W. (1993) Swimming Even Faster. Mayfield
Publishing, Mountain View, CA.
Marable, N.L., Hickson, J.F., Korslund, M.K., Herbert,
W.G., Desjardins, R.F. & Thye, F.W. (1979) Urinary
nitrogen excretion as influenced by a musclebuilding exercise program and protein intake variation. Nutrition Reports International 19, 795–805.
Meleski, B.W. & Malina, R.M. (1985) Changes in body
composition and physique of elite university-level
female swimmers during a competitive season.
Journal of Sports Science 3, 33–40.
Morgan, W.P., Costill, D.L., Flynn, M.G., Raglin, J.S. &
O’Connor, P.J. (1988) Mood disturbance following
increased training in swimmers. Medicine and Science
in Sports and Exercise 4, 408–414.
Mussini, E., Colombo, L., De Ponte, G., Calzi, M. &
Marcucci, F. (1985) Effect of swimming on protein
degradation: 3-methylhistidine and creatinine excretion. Biochemical Medicine 34, 373–375.
Novak, L.P., Woodward, W.A., Bestit, C. &
Mellerowicz, H. (1977) Working capacity, body composition and anthropometry of olympic female athletes. Journal of Sports Medicine 17, 275–283.
O’Sullivan, S., Sharp, R.L. & King, D.S. (1994) Carbohydrate ingestion during competitive swim training.
Journal of Swimming Research 10, 35–40.
Piehl, K., Adolfsson, S. & Nazar, K. (1974) Glycogen
storage and glycogen synthase activity in trained
and untrained muscle of man. Acta Physiologica Scandinavica 90, 779–788.
Sharp, R.L. (1986) Muscle strength and power as
related to competitive swimming. Journal of Swimming Research 2, 5–10.
Sharp, R.L., Troup, J.P. & Costill, D.L. (1982) Relationship between power and sprint freestyle swimming.
Medicine and Science in Sports and Exercise 14, 53–
56.
Sherman, W.M. & Maglischo, E.W. (1992) Minimizing
athletic fatigue among swimmers: special emphasis
on nutrition. In Sports Science Exchange, Gatorade
Sports Science Institute. 4, 35.
Stager, J.M., Cordain, L. & Becker, T.J. (1984) Relationship of body composition to swimming performance
620
sport-specific nutrition
in female swimmers. Journal of Swimming Research 1,
21–26.
Thorland, W.G., Johnson, G.O., Housh, T.J. & Refsell,
M.J. (1983) Anthropometric characteristics of elite
adolescent competitive swimmers. Human Biology
55, 735–748.
Tsintzas, K., Liu, R., Williams, C., Campbell, I. &
Gaitanos, G. (1993) The effect of carbohydrate ingestion on performance during a 30 km race. International Journal of Sport Nutrition 3, 127–129.
Van Erp-Baart, A.M.J., Saris, W.H.M., Binkhorst, R.A.,
Vos, J.A. & Elvers, J.W.H. (1989) Nationwide survey
on nutritional habits in elite athletes. Part I. Energy,
carbohydrate, protein, and fat intake. International
Journal of Sports Medicine 10 (Suppl. 1), 3–10.
Van Handel, P.J., Cells, K.A., Bradley, P.W. & Troup, J.P.
(1984) Nutritional status of elite swimmers. Journal of
Swimming Research 1, 27–31.
Walsh, R. & McNaughton, L. (1989) Effects of iron supplementation on iron status of young female swimmers during the pre-season phase of competition.
Journal of Swimming Research 5, 13–18.
Zawadzki, K.M., Yaspelkis, B.B. & Ivy, J.L. (1992)
Carbohydrate–protein complex increases the rate
of muscle glycogen storage after exercise. Journal of
Applied Physiology 72, 1854–1859.
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