An accumulation of international scientific evidence indicates that physical inactivity is detrimental to health and that moderate levels of physical activity confer significant health benefits. Unfortunately, in countries where major surveys of physical activity have been conducted, the prevalence of sedentary behaviour has been found to be as high as 40%. In the US, where approximately 30% of adults report little or no physical activity, the Centers for Disease Control and the American College of Sports Medicine recently issued guidelines and recommendations on the amount and frequency of moderate levels of physical activity necessary to elicit health benefits in predominantly sedentary adults. These guidelines utilise a physical activity-health paradigm and, uniquely, recommend the potential effectiveness of activities of daily living or "lifestyle activity' for achieving health benefits. This article briefly reviews the rationale behind these guidelines and, in view of the historical association of the exercise training-fitness model to health, highlights some challenges and potential problems in applying these new guidelines to the general population.