Exercise interventions to prevent and manage type 2 diabetes: physiological mechanisms.
Physical training is known to markedly increase insulin-mediated glucose uptake. This effect occurs predominantly in skeletal muscle and it has been shown in healthy individuals, people with impaired glucose tolerance and in patients with type 2 diabetes. The mechanism/s behind this adaptation includes an increase in glucose delivery, as well as an increase in glucose transport into the myocytes, and increases in glycolytic and oxidative enzyme activities. Furthermore, the capacity for glycogen synthesis increases with physical training. There has been less focus on the effect of physical training on insulin secretion, which is, however, known to decrease in the trained compared with the untrained state in healthy people. In patients with type 2 diabetes, in whom the β-cells have lost the capacity to secrete sufficient insulin in order to maintain normal glucose tolerance, the response to training is not a decrease in insulin secretion in response to a given stimulus. Rather, either no change or an increase is seen in the few studies that have been conducted. The mechanism for this opposite response is unknown, and this area needs high-quality intervention as well as cross-sectional studies.