Assess graduate-level understanding of the evidence and methods for evaluating the validity and reliability of wearable activity trackers for step count, heart rate, and energy expenditure in clinical and athletic populations; content includes comparator gold standards (e.g., direct observation, ECG, indirect calorimetry), common analytic approaches (ICC, Bland–Altman, MAE), study design and population-specific considerations, sources of measurement error, and implications for research and practice.