Exergames are popular video games that combine physical activity with digital gaming. To measure effects of exergame play on physical outcomes and health behaviors, most studies use external measures including accelerometry, indirect calorimetry, heart rate monitors, and written surveys. These measures may reduce external validity by burdening participants during gameplay. Many exergames have the capability to measure activity levels unobtrusively through monitors built into game equipment, and preliminary analysis indicates that exergame measures are significantly correlated with external measures of caloric expenditure, duration of play, and balance. Exergames also have unique capabilities to measure additional data, such as the game challenges, player movement, and levels of performance that affect aerobic activity. Researchers could capitalize on the data collected by the exergame itself, providing an efficient, unobtrusive, comprehensive measure of physical activity during exergame play.