The incidence of stress fractures of the lower extremities during U.S. military basic training is significantly higher among female military recruits than among male recruits. The prevalence of this injury has a marked impact on the health of service personnel and imposes a significant financial burden on the military by delaying completion of the training of new recruits. In addition to lengthening training time, increasing program costs, and delaying military readiness, stress fractures may share their etiology with the longer-term risk of osteoporosis.As part of the Defense Women’s Health Research Program, this book evaluates the impact of diet, genetic predisposition, and physical activity on bone mineral and calcium status in young servicewomen. It makes recommendations for reducing stress fractures and improving overall bone health through nutrition education and monitored physical training programs. The book also makes recommendations for future research to evaluate more fully the effects of fitness levels, physical activities, and other factors on stress fracture risk and bone health.