Energy systems refer to the physiological mechanisms through which the human body produces and supplies energy required for carrying out various activities. In Physiological Anthropology, the study of energy systems is important for understanding human adaptation, physical performance, metabolism, and variation in energy expenditure among individuals and populations. The immediate source of energy for cellular activities is adenosine triphosphate (ATP), but the body stores only a limited amount of ATP. Therefore, it continuously regenerates ATP through different energy systems. The three major energy systems are the ATP-PC system, the anaerobic glycolytic system, and the aerobic or oxidative system. These systems operate simultaneously, but their relative contribution varies according to the intensity and duration of physical activity. The ATP-PC system, also called the phosphagen system, provides energy for very short-duration, high-intensity activities. Muscles contain small amounts of stored ATP and phosphocreatine (PC). Phosphocreatine rapidly donates a phosphate group to ADP to regenerate ATP. This system does not require oxygen and produces energy very quickly. It is particularly important during