Introduction
In determining proper nutritional recommenda-
tions in a sport discipline, it is important to assess
the requirements of the sport and determine
whether substrate availability may limit perfor-
mance. In team sports such as basketball, rugby,
soccer, hockey, ice-hockey, volleyball and team
handball, the players perform many different
types of exercise. The intensity can alter at any
time and range from standing still to sprinting
(Fig. 44.1). This is in contrast to sports disciplines
such as a 100-m sprint and a marathon run, in
which during the entire event continuous exer-
cise is performed at a very high or at a moderate
intensity, respectively. Due to the intermittent
nature of team sports, performance may not only
be impaired toward the end of a match, but also
after periods of intense exercise. Both types
of fatigue might be related to the metabolic
processes that occur during match-play. There-
fore, before discussing the diet of athletes in team
sports, energy provision and substrate utiliza-
tion during intermittent exercise and in team
sports will be considered.
Energy production and substrate
utilization in team sports
In most team sports, the exercise performed is
intermittent. It is therefore important to know
how metabolism and performance during an
exercise bout are influenced by previous exercise.
Through the years, this has been investigated
systematically by changing one of the variables
at a time. Such studies form the basis for under-
standing the physiology of intermittent exercise.
It has to be recognized, however, that in most la-
boratory studies the variations in exercise inten-
sity and duration are regular, whereas in many
intermittent sports the changes in exercise inten-
sity are irregular and can be almost random.Anaerobic energy production
In one study, subjects performed intermittent
cycle exercise for 1 h, alternating 15 s rest and 15 s
of exercise at a work rate that for continuous
cycling demanded maximum oxygen uptake
(Essenet al. 1977). Considerable fluctuations in
muscle levels of adenosine triphosphate (ATP)
and phosphocreatine (PCr) occurred. The PCr
concentration after an exercise period was 40% of
the resting level, and it increased to about 70% of
the initial level in the subsequent 15-s recovery
period, whereas the increase in muscle lactate
was low.
Also during competition in team sports, the
PCr concentration probably alternates continu-
ously as a result of the intermittent nature of the
game. Figure 44.2 shows an example of the fluc-
tuations of PCr determined by nuclear magnetic
resonance (NMR) during three 2-min intermit-
tent exercise periods that each included short
maximal contractions, low-intensity contractions
and rest. A pronounced decrease of PCr was
observed during the maximal contractions, but it
almost reached pre-exercise value at the end of