GSTM1 and anemia: This phenomenon causes an increase in free Hb, which can cause Hb loss in the urine (hemoglobinuria); (iii) an iron deficiency anemia (the most common) [31]: since iron is necessary for oxygen transport and energy metabolism, in endurance athletes with iron deficiency, there can be a reduction in exercise capacity and VO2 max, the maximum amount of oxygen that the body can use [32].