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VOLUME 16 NUMBER 1 • JULY 2019
41
SA JOURNAL OF DIABETES & VASCULAR DISEASE
CLINICAL COMMENTARY
normal energy metabolism. Regular exercise decreases diabetic
patients’ hyperglycaemic state, which warrants adjustment in
insulin medication.
11
• Chronic resistance training increases skeletal muscle mass, which,
in turn, is responsible for 80% of insulin-mediated glucose
uptake.
12
The increased insulin-mediated glucose uptake is
derived from the breakdown of triglycerides into fatty acids and
glycerol (lipolysis) for the provision of energy. This physiological
benefit decreases blood glucose and adipose tissue, which is
beneficial to diabetic patients with the co-morbidity of obesity.
12
• Enhanced insulin sensitivity warrants exogenous insulin
adjustment.
13
Insulin is a hormone that converts glucose to
glycogen, thereby reducing blood glucose levels. Increased
insulin sensitivity allows lower dosages of insulin to more readily
facilitate this function, thereby preventing the pancreas from
secreting copious amounts of insulin, and thus helping to prevent
pancreatic hyperactivity. Insulin binds to the insulin receptor, which
then results in subcellular signalling and GLUT-4 translocation.
Diabetic patients experience decreased insulin sensitivity due to a
myriad possible errors ranging from problems with the binding of
insulin to the insulin receptor, to erros in the subcellular signalling
or GLUT-4 translocation. When a diabetic patient exercises, there
is a concomitant decrease in the amount of insulin secreted,
which upregulates the sensitivity of the insulin receptors, enabling
them to better identify the presence of blood glucose, thus
increasing glucose absorption into the muscle groups that are
being exercised.
12
Habitual muscle strength training increases the
resting metabolic rate of the patient, increasing blood glucose
uptake without augmenting insulin secretion.
12
• Regular structured exercise results in reduced plasma triglyceride
and cholesterol levels. During prolonged aerobic exercise,
triglycerides are broken down into fatty acids and glycerol
in order to be converted into glucose.
12
This is an additional
benefit for diabetic patients with the co-morbidities of obesity
and hypertension. Regular exercise helps to reduce obesity
and hypertension.
1
Obesity has been associated with insulin
resistance, which inhibits cells from readily identifying insulin
(decreasing insulin sensitivity).
1
Exercise-induced hyperglycaemia
may be affected by the exercise intensity. Higher exercise
intensities are more likely to promote enhanced hepatic
glycogenolysis (the decomposition of glycogen to glucose,
occurring in the liver in response to hormonal and neural
signals), resulting in hyperglycaemia.
The risks that diabetic patients should be aware of
when exercising
During exercise, diabetic patients undergo various cardiovascular
and hormonal changes aimed at ensuring an adequate supply
of glucose in order to meet the energy demand required by the
physical activity in which they are engaged. As a result, the patient
may experience exercise-induced hypoglycaemia, exercise-induced
hyperglycaemia, exercise-induced ketosis and post-exercise hypo-
glycaemia.
• Exercise increases post-exercise insulin sensitivity, which increases
glucose re-absorption in both exercised muscles and the liver
in an attempt to replenish glycogen stores. This physiological
phenomenon is called exercise-induced hypoglycaemia, which
can have severe, harmful effects on diabetic patients. It is therefore
imperative to amend the injected exogenous insulin dosage after
exercising in order to maintain a healthy energy balance.
14,15
• Exercise increases insulin absorption, which alters glucose
metabolism. Exercise-induced insulin absorption is further
increased when a patient injects insulin shortly before an exercise
bout or uses fast-acting insulin. It is therefore recommended that
patients exercise 60 to 90 minutes after insulin injections only.
The high level of insulin during exercise increases the conversion
of glucose to glycogen, while supressing glycogenolysis
(breakdown of glycogen to glucose) and gluconeogenesis
(glucose formation from non-carbohydrates), which may lead
to exercise-induced hypoglycaemia.
15
• Many diabetic patientsmay furthermore run the risk of developing
exercise-induced ketosis. Prolonged exercise increases peripheral
glucose absorption of the exercising muscles, thereby stimulating
lipolysis (breaking down of triglycerides into glycerol and fatty
acids for the use of energy) and hepatic glucose production (the
formation of glucose from lactate and amino acids within the
liver, primarily regulated by insulin and glucagon) and ketogenesis
(the breaking of fatty acids for energy, producing ketones).
16
It is
recommended that diabetic patients check their blood glucose
and urine ketone levels before commencing an exercise session.
If their blood glucose concentration is higher than 250 mg/dl
(13.88 mmol/l) and/or ketones or blood are visible in their urine,
exercise should be postponed and the exogenous insulin dosage
adjusted.
15
• After exercise the individual experiences a state of exercise-
induced hyperglycaemia for a period of five to 15 minutes. This
is due to the need for increased glucose re-absorption into the
exercised muscle in order to replenish the glycogen stores. In
diabetic patients, the state of exercise-induced hyperglycaemia
may however occur for a period far longer than the normal
five to 15 minutes, and this may lead to adverse conditions.
14
Careful monitoring of blood glucose levels during and after
exercise is therefore essential in order to prevent this scenario.
Many diabetic patients experience enhanced insulin sensitivity,
resulting in increased re-absorption of glucose, producing
a state of post-exercise hypoglycaemia. Frontera
et al
. and
Trefts
et al
. postulated that this occurs due to increased insulin
sensitivity, which allows more glucose to be absorbed into the
previously exercised muscles, only to be converted and stored
as glycogen.
16,17
Various recommendations have been proposed
concerning overcoming post-exercise hypoglycaemia, including
decreasing the pre-exercise dosage of insulin, avoiding fast-
acting exogenous insulin immediately before exercising, and
the consumption of a balanced and appropriate post-exercise
meal.
15,17
Exercise therapists in South Africa
Physiotherapists and biokineticists are Health Professions Council
of South Africa-affiliated paramedical exercise therapists. Exercise
rehabilitation and therapy falls within their scope of profession.
18
Type 1 diabetic adolescents and adults who employ exercise
regimes in order to enhance their sports performance at elite
competitive levels are strongly encouraged to consult both a
biokineticist and an exercise scientist due to their complicated
intrinsic energy metabolism and exercise programme prescription
requirements. Non-insulin-dependent diabetics with CAD and
obesity co-morbidities should consult a biokineticist before starting
to exercise, to avoid the inherent exercise-induced risks. Diabetic