Dr. Jasem Ramadan, Associate Professor Department of Physiology, Faculty of Medicine, Kuwait University.

Introduction and objectives: One of the most important questions for all those who have an interested in the topic of physical activity (PA) and health is how much PA is needed in adults to prevent morbidities, disabilities, and premature death? There has been a considerable debate about the issue of the "dose-response" (frequency, intensity, duration, type) in relation to the role of PA in enhancing health, and in the prevention of disease, disability, and premature death. The aim of this presentation is to outline the updated evidence-based knowledge about the subject of dose-response relationship as it impact on PA and health benefits. Method: Objective measurements of frequency, duration (time), and intensity (absolute and relative) and the subjective assessments such as "little, moderate and heavy" or field studies (questionnaire, PA records and recall diaries) will be addressed, fractionalization of PA) comparing one continuous session of exercise with several short sessions of the same total duration; or 2) comparing a session of moderate-to-hard exercise with a session of longer duration, lower intensity, but equivalent energy expenditure, i.e., "trading intensity for duration. Results and discussion: There is evidence for a dose-response relationship between the volume of PA and all-cause mortality rates in adult women and men of all ages from the United States and Europe. The minimal effective dose is not well defined, but PA expending 1000 kcal.wk-1 (4200 kJ.wk-1) is associated with approximately 30% reduction in all-cause mortality rates. There is an inverse dose-response relationship between PA and both the incidence and mortality rates from all cardiovascular and coronary heart disease. Training at about 50% of maximal exercise tolerance is shown to be effective in reducing blood pressure, while training at high-intensity levels does not appear to provide additional benefits. There is a dose-response relationship between PA and the risk for colon cancer, prevention of type 2 diabetes, over weight, prevention of osteoporosis, depression and anxiety, and an improvement in activity of daily living.
Conclusion: Regular PA produces a number of major health benefits. It is associated with a reduction in all-cause mortality, fatal and nonfatal total cardiovascular disease, and coronary heart disease. Regular PA is also associated with a reduction in the incidence of obesity and type 2 diabetes mellitus and reduction in the incidence of colon cancer, blood pressure and osteoporosis.