This monograph addresses subjective perception of exertion during physical activity, summarizes the current level of information in this area and presents research results. The research section presents the scholar’s use of the Borg RPE (Rating of Perceived Exertion) scale when working with cardiac patients. The Borg scale is a laboratory method that helps individuals perceive the relation between the subjective sensation of exertion and objective indicators of cardio-vascular exertion. This helps