Several factors determine the intensity of a workout, including duration, exercise type, body weight, and personal fitness level. Heart rate is a common measure; higher heart rates generally indicate greater intensity. Additionally, the choice between aerobic or anaerobic activities influences intensity, with high-intensity interval training (HIIT) typically being more demanding. Environmental conditions, such as heat or humidity, can also affect perceived exertion. Tailoring workouts to individual capabilities ensures optimal benefits while minimizing injury risks.