Diabetic Mellitus – Type 2 and exercise
Diabetes mellitus (DM)
Diabetes mellitus (DM) is a common chronic condition, occurring both in young people (usually type 1 diabetes mellitus) and, more often, in adults (type 2 diabetes mellitus). Another type of DM is the gestational diabetes, which is a secondary DM that manifests as a complication of other diseases or side effects from drugs, etc.
This condition is due to insufficient secretion of insulin by the pancreatic cells, as well as to the increased resistance of the cells to the action of insulin. The main feature is the appearance of hyperglycemia (increased blood sugar), it disrupts the metabolism of carbohydrates, proteins, fats, water and electrolytes and is usually due to insufficient secretion of insulin by the cells of the pancreas.
According to the guidelines of the American Diabetes Association, the diagnosis of diabetes is made based on the presence of one of the following criteria:
- glycosylated hemoglobin ≥6.5%,
- plasma (fasting) glucose ≥126 mg/dl (7.0 mmol/l),
- 2-h plasma glucose ≥200 mg/dl (11.1 mmol/l) in a glucose tolerance test after taking 75 g of glucose, and the presence of classic symptoms of hyperglycemia (such as polyuria, polydipsia, unexplained weight loss) or the onset of a hyperglycemic crisis (increase in plasma glucose ≥ 200 mg/dl or 11.1 mmol/l).
A person can be classified as prediabetic if the value of glycosylated hemoglobin is 5.7–6.4%, plasma glucose (fasting) 100–125 mg/dl (5.6–6.9 mmol/l) or 2-h plasma glucose in a test glucose tolerance 140–199 mg/dl (7.8-11.0 mmol/l).
Although the exact causes of the disease are not completely clear, important predisposing causes are heredity, obesity, age and sex, poor diet, sedentary lifestyle, viral infections (usually Coxsackie B), autoimmune disorders, , endocrine diseases etc.
The disease mainly affects the vessels and nerves of the body. In blood vessels, it usually causes damage to their basement membrane (capillaries) or lesions of their inner lining (arteries) that lead to atherosclerosis. For this reason, diabetic patients often show ischemic heart disease, hypertension, obstructive lesions in the arteries mainly of the lower extremities, damage to the peripheral nerves, the vessels of the eyes (retinopathy), glomerulus from the kidneys and results in chronic renal failure), skin lesions, etc.
The main goal in the treatment of type 2 DM is to achieve and maintain normal levels of glucose and excellent lipid levels, with the aim of preventing or delaying microvascular, macrovascular and neurological complications.
DM treatment also concludes special diet programs (reduced carbohydrate intake), administration of drugs such as insulin, oral antidiabetic drugs, as well as the implementation of regular physical activity programs.
Also, the placement of continuous insulin infusion pumps and pancreas transplantation are applied in patients usually with type 1 diabetes.
Exercise results in DM
According to the international literature it has been observed that regular exercise improves glycemic control and lipid profile, as well as cardiorespiratory adequacy, cardiac function and the function of the autonomic nervous system of diabetic patients.
More specifically, many researchers have found that systematic physical activity:
- Reduces fasting glucose and glycosylated hemoglobin levels and increases insulin sensitivity. Regarding the lipid profile of patients, it causes a decrease in LDL and an increase in HDL levels.
- Improves aerobic capacity and the ability to perform physical work.
- Improves left ventricular function by increasing pulse volume, cardiac output, ejection fraction and diastolic function.
- Improves heart rate variability, both in time and frequency domain. The improvement of these indicators was more evident in the group of diabetic patients with CKD.
- Leads to all the other known beneficial effects of exercise.
Mechanisms that improve glycemic control due to regular exercise are increased insulin action in peripheral tissues, increased rate of glucose clearance by the liver, decreased rate of glucose production by the liver and increased glucose utilization by skeletal muscles. It is argued that the strongest beneficial effect of exercise is the enhancement of insulin action in peripheral tissues, which is attributed to both increased blood flow to skeletal muscle and to a reduction in insulin resistance. Increased insulin activity in muscle has been shown to be associated with increased GLUT-4 receptors, as well as enzymes, which regulate glucose storage and burning in muscle.
Moreover, body changes that exercise causes in the morphology of the muscles, is an important factor of increased muscle sensitization to insulin. Systematic aerobic exercise is known to increase the density of muscle capillaries and convert type IIb to IIa muscle fibers, which have increased amounts of glucose transporters and respond better to insulin.
Although insulin resistance in peripheral tissues is the main abnormality in patients with type 2 diabetes, a secondary disorder is increased production and decreased hepatic glucose clearance. In healthy individuals it has been found that regular exercise can lead to a reduced rate of hepatic glucose production during exercise, due to both reduced glycogenolysis and gluconeogenesis, but without altering glucose kinetics at rest.
On the contrary, it has been found that in both obese and diabetic patients, regular exercise causes an increased rate of glucose clearance from the liver. Therefore, regular exercise can improve the metabolic control of patients with type 2 diabetes, both by increasing insulin sensitivity in peripheral tissues and by improving glucose production in the liver. Exercise leads to a significant improvement in the lipid profile as shown by lowering triglyceride levels, total cholesterol and increasing HDL levels. It is argued that regular exercise improves metabolic control in certain age groups, such as young people and people aged between 40-54 years old.
Factors that contribute to patients’ physical fitness improvement with exercise are the beneficial cardiovascular (central) adjustments, such as the reduction of resting heart rate, the increase of pulse volume and cardiac output, and the improvement of diastolic dysfunction, as well as improving the action of the autonomic nervous system in the heart. Furthermore, to a large extent contribute the beneficial adjustments to the skeletal muscles (peripheral), which lead to an increase in arteriovenous oxygen difference, muscle strength and endurance.
The mechanisms through which exercise improves the action of the cardiac autonomic nervous system, especially in patients with its dysfunction, are not fully established. It may be the result of morphological adjustments in the heart from long-term exercise, either e.g. of cardiac hypertrophy, or an effect on the function of myocardial pacemaker cells.
In addition, changes caused by regular exercise in catecholamine concentrations, seem to improve the total functioning of the autonomic nervous system.
Also, centrifugal stimulus from chemoreceptors in the muscles seem to control the sympathetic and parasympathetic flow of stimuli to the heart, which indicates the link between improving the function of the autonomic nervous system and improving muscle function.
Instructions for safe exercise in patients with DM Careful patient testing for the possible presence of concomitant diseases (cardiovascular diseases, retinopathy, diabetic kidney disease, etc.).
Gradual increase in the intensity and duration of exercise. Learning affordable self-monitoring methods for blood sugar levels.
Avoid exercising during the hours when the effect of the insulin administered is at its maximum.
Take a light meal 20-30 min before exercise.
Avoid insulin injections in the extremities that are more exercised during exercise. Due to increased perspiration they accelerate its absorption.
Information on how to deal with hypoglycemia during exercise, which can sometimes occur late.
Exercise instructions for diabetic patients
Patients with type 2 DM should, if there are no contraindications and all the safety instructions are followed, develop daily or at least 4-5 days a week, a physical activity session for about 30 minutes, which can be cumulative (e.g. 3x10 minutes). The simplest forms are brisk walking, cycling and swimming. Of course, organized exercise programs in gyms with aerobic exercises, resistance exercises (3-4 times per week), which favor the greater use of glucose by the muscles and prevent their atrophy, and flexibility exercises offer the best results.
The variety of programs, including modern exercise programs, can act as a magnet for diabetics and possibly reduce their withdrawal rates from therapeutic exercise programs. It is therefore concluded that regular physical activity programs should be included in patients’ treatment with type 2 diabetes.