Disease prevention may be considered at three levels: primary (avoiding disease occurrence), secondary (early detection and reversal), and tertiary (prevention or delay of complications). Physical exercise could potentially contribute to all of these. Metabolic studies suggest the major effect of exercise is at the level of insulin sensitivity/resistance. Therefore, it may have the greatest benefit in primary prevention and in the early stages of the disease. Studies of migrants and of active and inactive professions support this notion. There is also provisional support for the benefit of exercise on metabolic control and prevention or delay of chronic complications in non-insulin-dependent (type II) diabetic patients. In designing a trial of exercise, aspects such as single/multifactorial intervention, the age range of subjects, and choice of outcome measures must be considered. The most widely used methodological tool in assessing physical activity levels in population studies is the activity questionnaire, which is nonreactive, practical, applicable, and accurate relative to other methods. A positive approach to exercise training for both the patient with type II diabetes and the general community appears to be warranted. However, trials examining the efficacy of activity intervention, with independent evaluation of both short- and long-term outcomes, are still needed.

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