A brief summary of the consensus conference on "Physical Activity for Preventive Purposes" held in Nancy on November 22, 2005. Experts recommend sixty minutes of physical activity—moderate or vigorous—per day for children and adolescents, and thirty minutes of moderate activity (such as brisk walking) for adults. These are the thresholds at which beneficial health effects have been proven. They also recommend physical activity for people with chronic diseases, an essential component of their care.