Body composition is a significant determinant of health and performance. Obesity, with its attendant health risks, is a major public health concern. Although not typically associated with athletes, participants in sports in which high body mass is an advantage can be at risk for excess body fat. Conversely, athletes in sports in which low mass for height is advantageous can be at risk for too low levels of body fat, low muscle mass for height, and low bone mass. Females with low body fat and restricted energy intake may experience oligomenorrhea or amenorrhea, which can lead to impaired musculoskeletal development in growing girls or bone loss in adults. Boys with high levels of activity and restricted energy and nutrient intake may also experience slowed growth. ...