Current definitions of an athlete range from loosely defined to overly restrictive, rely on qualitative subjective descriptors, and fail to capture the majority of physically active patients. To improve the understanding between exercise and health metrics a more standardized and granular classification of exercising patients is required. We propose a simplified algorithm to categorize and define exercising patients based on the: (1) intent of exercise, (2) volume of exercise (hours/week), and (3) level of competition. Further classification of physically active patients can be derived based on the intensity and volume of activity using metabolic equivalent-hours per week. In conclusion, a formal framework to classify athletes and quantify both the volume and intensity of exercise will enable more precise and meaningful associations between exercise and health outcomes.