Public health surveillance of physical activity.

There is a clear public health need to measure and track physical activity behavior. Surveillance systems should be flexible enough to keep up with scientific advances in identifying dose-response relationships and in developing new assessment techniques, and new ways to assess community indicators associated with physical activity. Having a strong public health surveillance system that produces data that can be used to plan, guide, and evaluate programs is essential for increasing the prevalence of an important health-related behavior: physical activity.