This document discusses physical activity epidemiology and related methodologies. It defines epidemiology as the study of health events in populations and describes methods used in physical activity epidemiology like questionnaires, diaries, and technology to measure physical activity. It also summarizes common study designs in epidemiology including cross-sectional, case-control, cohort, and randomized clinical trials. The document outlines assessment of causality and key journals, educational requirements, and job opportunities in physical activity epidemiology.