NUTRITION IN SPORT

the high aerobic energy utilization is that oxygen
uptake in the recovery periods after intense exer-
cise is high (Bangsbo 1994a).

Substrate utilization

The large aerobic energy production and the pro-
nounced anaerobic energy turnover during
periods of a match in many team sports are asso-
ciated with a large consumption of substrates.
The dominant substrates are carbohydrate and
fat, either stored within the exercising muscle or
delivered via the blood to the muscles.
The carbohydrate used during a match is
mainly the glycogen stored within the exercising
muscles, but glucose extracted from the blood
may also be utilized by the muscles. Information
about the use of muscle glycogen during a match
can be obtained from determinations of glycogen
in muscle samples taken before and after the
match. The difference in glycogen content repre-
sents the net utilization of muscle glycogen, but it
does not show the total glycogen turnover, since
some resynthesis of glycogen probably occurs
during the rest and low-intensity exercise
periods during a match (Nordheim & Vøllestad
1990; Bangsbo 1994a). Muscle glycogen utiliza-
tion may be high in team sports. As an example,

576 sport-specific nutrition

in a study of Swedish soccer players the average

thigh muscle glycogen concentrations of five

players were 96, 32 and 9 mmol · kg–1wet weight

before, at half-time and after a non-competitive

match, respectively (Saltin 1973). An important

aspect to consider in intermittent sport is that

even though the muscle glycogen stores are not

completely depleted, the level of muscle glyco-

gen may be limiting for performance (see below).

Fat oxidation is probably high during most

team sports. Studies focusing on recovery from

intense exercise and intermittent exercise

suggest that fat is oxidized to a large extent after

intense exercise (Essen 1978; Bangsbo et al. 1991).

The primary source of the fat oxidized in the rest

periods in between the more intense exercise

may be muscle triacylglycerol (Bangsbo et al.

1991).

The role of protein in metabolism in team

sports is unclear, but studies with continuous

exercise at a mean work rate and duration similar

to team sports such as soccer and basketball have

shown that oxidation of proteins may contribute

less than 10% of the total energy production

(Wagenmakers et al. 1990).

As an example, an estimation of substrate uti-

lization and energy production during a soccer

game is shown in Fig. 44.3. It is clear that muscle

300

0

250

150

50

Protein

Substrate utilization (g)

Aerobic

100

96

40

20

Energy turnover (%)

200

100

0

60

80

98

Fat

Blood

glucose

Muscle

glycogen

Anaerobic

ATP + PCr

Fig. 44.3Estimated relative

aerobic and anaerobic energy

turnover (right) and

corresponding substrate

utilization (left) during a soccer

match. Adapted from Bangsbo

(1994a), with permission from

Acta Physiologica Scandinavica.