concentrations are required to remove glucose,
and in line with this, highly trained people
have lower circulating insulin levels and a re-
duced insulin response to a glucose challenge.
However, the increased insulin sensitivity
during and after exercise increases the risk for
hypoglycaemia in insulin-treated diabetics.
Insulin-dependent diabetes mellitus
In people with IDDM, insulin secretion is lacking
or insufficient because of an almost total destruc-
tion of the insulin secreting b-cells in the pan-
creas. The b-cells are destroyed by the diabetic’s
own immune system (autoimmune destruction).
IDDM is treated with life-long insulin therapy by
insulin injection several times each day. Insulin is
produced as long-acting (elevates blood insulin
concentration for many hours) and rapid-acting
(elevates blood insulin for a much shorter period
of time) forms and most patients take a mixture
of both forms. In the evening (and some times
morning), long-acting insulin is injected to main-
tain the basal insulin concentration. Before each
meal, rapid-acting insulin is injected to stimulate
removal of the absorbed glucose. The insulin
dose required depends on the individual and it is
important to measure glucose concentration
often to establish the correct dose.
Exercise training for IDDM
IDDM normally develops at a young age and
exercise is a natural activity for children. It is par-
ticularly important for their social development
that they get the opportunity to participate in
group exercises with other children. Although
some children with IDDM develop fear of
participation in sports, exercise is regarded as
safe if children with IDDM are educated to adjust
their dose of insulin to the intensity of exercise.
Many people with IDDM participate in sport and
there are several examples of athletes at the top of
their sports.
These athletes clearly show that it is possible
for diabetic athletes to achieve a high perfor-
mance level. In non-diabetics, exercise training
460 special considerations
causes adaptations in skeletal muscle and circu-
latory system which is the background to the
increased performance (Holloszy & Booth 1976).
People with IDDM seem, however, to respond to
training in a similar way and there are therefore
no physiological reasons for not participating in
sport (Wallberg-Henriksson 1992).
Exercise training for people with IDDM is,
however, not without problems. The insulin con-
centration is important for control of the glucose
concentration and too high a concentration of
insulin in combination with exercise may cause
hypoglycaemia. Too low a concentration of insu-
lin, on the other hand, may cause elevation in
blood glucose and ketoacidosis. The greatest
problem is the development of hypoglycaemia
because of the inability to regulate prevailing
blood insulin concentrations. In people with
IDDM the insulin concentration in blood will
depend on the amount of insulin administered
and the rate of release of insulin from the site of
injection. The normal decrease in insulin level
during exercise will therefore not occur in people
with IDDM and, as exercise increases insulin sen-
sitivity, glucose uptake in skeletal muscles may
be too high. To mimic the reduction in concentra-
tion of insulin that occurs in normal subjects
during exercise, insulin injections have to be
avoided immediately prior to exercise in people
with IDDM.
Before exercise, it is important that the glucose
and insulin concentrations are neither too high
nor too low (Horton 1988). The concentration of
glucose should be measured to give information
about the insulin level. If the blood glucose con-
centration is below 5 mm,it may be a result of too
high a concentration of insulin and there is a high
risk for hypoglycaemia if exercise is performed.
It is therefore not advised to participate in exer-
cise, and glucose should be taken to raise the
blood glucose concentration before exercise is
performed. Furthermore, it is important that
athletes with IDDM should be able to recognize
the symptoms of hypoglycaemia and respond
accordingly.
Exercise is not recommended when the blood
glucose concentration is above 16 mm(Wallberg-