The daily requirement of iron for girls is 18 mg. Most girls don't take that much in. And excessive sweating can further exacerbate irion loss. As with all women, menstruation icreases iron intake needs. Iron deficiency or inadequate iron stores can occur without anemia and this is common in young female athletes.
Training causes the fluid in the blood to increase.
This test indicates iron stores in the body. Caffeine intake blocks iron uptake. Calcium Calcium intake is another nutrient where female athletes have higher needs, but fall far short of the mark. Stress fractures which can sideline a girl for the remainder of a season are the most tangible risk. Wieght bearing sports, those than involve running or jumping, are at greatest risk.