The beneficial effects of physical exercise on the decreased insulin sensitivity caused by detrimental lifestyle were reviewed based on experimental evidences. In epidemiological studies, disease prevention has been considered at three levels: primary (avoiding the occurrence of disease), secondary (early detection and reversal), and tertiary (prevention or delay of complications). The major purpose of physical exercise for primary prevention and treatment of lifestyle-related diseases is to improve insulin sensitivity. It is known that, during physical exercise, glucose uptake by the working muscles rises 7 to 20 times over the basal level, depending on the intensity of the work performed. However, intense exercise provokes the release of insulin-counter regulatory hormones such as glucagons and catecholamines, which ultimately cause a reduction in the insulin action. Continued physical training improves the reduced peripheral tissue sensitivity to insulin in impaired glucose tolerance and Type II diabetes, along with regularization of abnormal lipid metabolism. Furthermore, combination of salt intake restriction and physical training ameliorates hypertension. In practical terms, before diabetic patients undertake any program of physical exercise, various medical examinations are needed to determine whether they have good glycemic control and are without progressive complications. Because the effect of exercise that is manifested in improved insulin sensitivity decreases within 3 days after exercise and is no longer apparent after 1 week, a continued program is needed. For a safety practice, moderate- or low-intensity exercise is preferable. In conclusion, we have found sufficient evidences that support the theory that, combined with other forms of therapy, mild exercise training increases insulin action despite no influence on body mass index or maximal oxygen uptake. Along with evident benefits in health promotion, moderate-intensity exercise might play an important role in facilitating treatment of various diseases.