There are two fundamental assumptions in epidemiology:

1.Human disease is not random

2.Human disease has causal and preventative factors that can be identified through scientific investigation of different populations or subgroups of individuals within a population (Hennekens, 1987).

The primary goal of epidemiology is to identify the determinants of health and disease to decrease mortality (death) and morbidity (a diseased condition or state) within a population (Kuller, 1987). Physical Activity Epidemiology, therefore, focuses on physical activity within populations and investigates how physical activity levels impact health and disease to decrease mortality and morbidity. Physical Activity Epidemiology typically incorporates both the assessment of physical activity, as well as, intervention efforts focusing on increasing physical activity.