By Dr. Massimo Golia
Type 2 diabetes mellitus includes a heterogeneous group of metabolic diseases, characterized by chronic hyperglycemia and disorders of carbohydrate, lipid and protein metabolism, deriving from the lack of production and / or the resistance of peripheral tissues to the action of insulin . Type 2 diabetes mellitus is said of the adult because in general the pathology appears after the age of 40; unlike type 1 diabetes, in type 2 there is no absolute lack of insulin, but the target tissues show pathological resistance to its action.
Obesity is present in over 80% of patients with type two diabetes mellitus. It is accompanied by insulin resistance and hyperinsulinism compensating for hyperglycemia. Obesity plays a major role in the development of insulin resistance; in fact, adipose tissue is able to produce a series of substances (leptin, TNF-α, free fatty acids, resistin, adiponectin), which contribute to the development of insulin resistance. Furthermore, in obesity, adipose tissue is the site of a state of chronic low-intensity inflammation, which is a source of chemical mediators that aggravate insulin resistance.
Effects of physical activity / exercise and training on diabetic patients
For decades, physical exercise, combined with proper nutrition, has been considered a useful tool for diabetics. However, it is only for about 20 years that - based on the results of the numerous studies carried out - the international scientific community is unanimous in stating that regular exercise is effective not only in prevention, but also in the treatment of diabetes.
Studies have shown, in fact, that the effects of physical exercise are carried out both in acute (that is, after a single session) and in "chronic" (after a period of training) and at different levels: insulin sensitivity, transport of glucose and other risk factors related to diabetic disease; let's see them in detail.
Insulin sensitivity
Insulin resistance is a common anomaly in type 2 diabetes.
In subjects in the early phase of type 2 diabetes, insulin resistance reduces insulin-mediated glucose uptake by 35-40% compared to healthy individuals. Insulin-mediated glucose uptake occurs mainly in skeletal muscles and is directly related to the amount of muscle mass and inversely correlated with fat mass. Studies have shown that exercise increases peripheral insulin sensitivity in individuals with type 2 diabetes, and that this increased sensitivity persists from 24 to 72 hours post-exercise.
The effect of acute physical exercise on the mechanism of insulin sensitivity is lost in a few days, so that for this effect to continue the exercise must be carried out constantly and with no more than 2 days without effecting it.
Glucose transport
Muscle glucose uptake requires three steps. These are the transport of glucose from the blood to the muscle, the transport of glucose through the cell membrane and the phosphorylation of glucose within the muscle.
Schematic representation of the control of the entry of glucose into skeletal muscle during muscular work.
The only glucose transport gradient would not be sufficient to support glucose uptake during exercise, physical if blood flow and capillary recruitment were not increased. The increased blood flow is necessary to cope with the increased demands for oxygen and nutrients. Furthermore, the increase in blood flow is also accompanied by the opening of normally unused capillaries, so as to increase the circulation of the muscle.
The second step is the transport of glucose into the cell. This transport takes place at the level of the skeletal musculature using glucose transporters 4 (GLUT-4). Exercise is able to increase glucose transport within the cell, stimulating the translocation of GLUT4 from the cytosol to the cell surface.
Finally, the last step involves glucose phosphorylation by the hexokinase. Exercise has been shown to increase the levels of hexokinase in skeletal muscle.
