Introduction: The practice of physical exercise causes physiological changes in the body and among them the increase in the rate of production of heat and sweating. The sweat production and subsequent evaporation thermoregulatory mechanism is more efficient, however, dehydration can compromise performance. There are several ways to evaluate the changes in hydration levels after the practice of physical exercise and among them, the measure of acute changes in body weight before and after exercise. Objective: To evaluate the changes in hydration levels of marathon runners after athletics. Materials and Methods: A total of 6 athletes athletics, the national average age of 29.67 years, fit the practice of competitive exercises. The study took p...