is therefore required that glucose, which can
be rapidly absorbed, is available when IDDM
athletes perform exercise training, to prevent
hypoglycaemia and to reduce the risk of coma
if hypoglycaemia occurs. This is particularly
important when running or cycling is performed
in conditions where it will be difficult to obtain
carbohydrates.
It seems that ingestion of 40 g carbohydrate ·
h–1is sufficient to avoid hypoglycaemia (Sane et
al.1988). Athletes with IDDM performed a 75-km
ski race and ingested glucose at an average rate
of 40 g · h–1(more in the later part of the exercise);
ingestion of glucose at this rate prevented
hypoglycaemia when insulin injection also was
reduced (Fig. 34.2). The glucose concentration
was, however, in the lower range for many of the
IDDM athletes at the end and more glucose may
have improved performance. Horton (1988) sug-
gested that glucose should be ingested at a rate of
462 special considerations
70–80 g · h–1during prolonged exercise. In normal
subjects, glucose ingestion at a rate of 60 g · h–1is
recommended (Costill & Hargreaves 1992) and
glucose should be ingested at the same rate in
athletes with IDDM. Furthermore, in addition to
supply of carbohydrates, athletes with IDDM
must always be aware of the risk of hypogly-
caemia and ingest glucose when symptoms of
hypoglycaemia come.
Exercise per sestimulates glycogen synthesis
after the training session when glucose is avail-
able. In diabetics, regulation of blood glucose
concentration is normally the focused subject
and glycogen synthesis in skeletal muscles is
regarded prerequisite for regulation of blood
glucose. In sport, on the other hand, the replen-
ishment of muscle glycogen stores is normally
viewed from a performance perspective. Muscle
glycogen is the most important energy substrate
in most types of sport and for optimal perfor-
mance, it is important that the glycogen stores
are replenished after each bout of exercise (Ivy
1991). Glycogen can be synthesized in people
with IDDM even in the absence of insulin injec-
tion after exercise (Mæhlum et al.1978). In the
absence of insulin, however, only half of the
glycogen store seems to be replenished (Fig.
34.3). Injection of insulin is therefore necessary
for optimal glycogen synthesis, even though the
administration of insulin after exercise increases
the risk for hypoglycaemia.Conclusion
The nature and intensity of any exercise training
programme combined with the personal require-
ments of a person with IDDM make it difficult to
generalize about factors, such as dose of insulin
administered before exercise and amount of
dietary intake. Monitoring the concentration of
glucose prior to any exercise ensures that the per-
formance is not undertaken in conditions which
may be adverse for the IDDM subject. If the
blood glucose level is low then the intensity of
exercise should be decreased or delayed until
ingested carbohydrate has time to boost the
blood glucose concentration. High blood glucose(^103375)
Blood glucose (mmol
–1.I
)
24
20
16
12
8
4
0
Distance (km)
Fig. 34.2Blood glucose concentration (individual and
mean) in athletes with IDDM during a 75-km ski race.
The shaded area shows healthy controls. The athletes
with IDDM reduced their daily insulin dose by about
35% and ingested about 270 g of carbohydrate during
the exercise (36 g · h–1). Adapted from Sane et al.(1988).