minerals and vitamins
Food and drink supplies the body with fluids,
energy-producing substrates, and other impor-
tant components, such as salt, minerals, and vita-
mins. In a well-balanced diet, most nutrients are
supplied in sufficient amounts. However, there
can be some exceptions.
Iron is an important element in haemoglobin,
which binds to the red blood cells and aids in the
transport of oxygen throughout the body. There-
fore, an adequate iron intake is essential for ath-
letes and especially for female athletes, who lose
blood and, thus, haemoglobin during menstrua-
tion (see Chapter 24). The recommended daily
intake of iron for a player is approximately
20 mg, which should be ingested via solid foods
rather than in tablet form, as iron found in solid
foods is more effectively absorbed from the intes-
tine to the blood. Animal organs (liver, heart and
kidneys), dried fruits, bread, nuts, strawberries
and legumes are foods with a high content of
iron. It is advisable to increase iron intake in
periods when players are expected to increase
their red blood cell production, e.g. during the
preseason or when training at a high altitude.
A question commonly asked is whether or not
players should supplement their diet with vita-
mins. In general, vitamin supplementation is
not necessary, but there are conditions where it
might be beneficial. For example, it is advisable
to enhance vitamin E intake when training at
high altitudes, and to use vitamin C and multiple
B-vitamin supplements in hot climates (see
Chapters 20 and 26).
creatine
In team sports, the rate of muscle PCr utilization
is high during periods of match play and in the
following recovery periods PCr is resynthesized
(see above). This leads to the question whether
an athlete in team sports can benefit from inges-
tion of creatine in a period before a match, as it
has been shown that intake of creatine increases
the PCr and particularly creatine levels in
muscles (Harris et al. 1992). For example, it was
582 sport-specific nutrition
found that five subjects increased their total
muscle creatine level (PCr and creatine) by 25%
after a creatine intake of 20 g · day–1for 5 days
(Greenhaff et al. 1994). The effect of intake of crea-
tine is discussed in detail in Chapter 27 and the
discussion here will focus on issues relevant to
the team games players.
An elevated level of creatine and PCr may
affect PCr resynthesis after exercise (Greenhaff et
al.1994), which may have an impact on the
ability to perform intermittent exercise. In one
study, subjects performed 10 6-s high-intensity
exercise bouts on a cycle-ergometer separated by
24 s of rest, after they had ingested either creatine
(20 g · day–1) or placebo for a week (Balsom et al.
1993a). The group which ingested creatine had a
lower reduction in performance as the test pro-
gressed than the placebo group. On the other
hand, as one would expect, creatine ingestion
appears to have no effect on prolonged (>10 min)
continuous exercise performance (Balsom et al.
1993b).
Although creatine ingestion increases muscle
PCr and creatine concentration, it is doubtful that
athletes in team sports, except probably for vege-
tarians, will benefit from creatine supplementa-
tion, since creatine ingestion also causes an
increase in body mass. It is still unclear what
causes this increase, but it is most likely due to an
increased accumulation of water. Nevertheless, a
gain in body weight has a negative influence in
sports in which the athletes have to move their
body mass against gravity. For example, no dif-
ference in performance during intense intermit-
tent running (Yo-Yo intermittent recovery test)
was observed when a group of subjects per-
formed the test after 7 days of creatine intake
(20 g · day–1) compared with a test under control
conditions. Furthermore, it is unclear how
ingesting creatine for a period influences the
body’s own production of creatine and the
enzymes that are related to creatine/PCr synthe-
sis and breakdown. It may be that an athlete,
through regular intake of creatine, reduces his
ability to produce PCr and creatine, which may
result in a reduction in the PCr and creatine
levels when the athlete no longer is ingesting