PROJECT SUMMARY/ABSTRACT Restrictive eating disorders (EDs) most commonly affect female adolescents and can lead to low bone mineral density (BMD) and impaired bone microarchitecture. Peak bone accrual occurs during adolescence, and the presence of a restrictive ED at this time can increase the risk of osteoporosis into adulthood. Weight-bearing physical activity can promote bone accrual, but the bone health benefits may be reduced with an ED. Physical activity participation is often restricted during ED treatment due to concerns for compulsive exercise (i.e. rigid and highly-driven exercise behaviors) and interference with weight restoration. Data is lacking regarding if, when, and how patients return to physical activity and the associations with compulsive exercise and eating disorder behaviors during ED recovery. Additionally, the changes in BMD and bone microarchitecture, and the impact of weight-bearing physical activity on bone health in female adolescents as they recover from a restrictive ED are unknown. Addressing these knowledge gaps is essential to inform the clinical approach to physical activity integration and optimization of bone health during ED recovery among female adolescents. Dr. Aubrey Armento will conduct a prospective longitudinal clinical study of female adolescents admitted to the Children’s Hospital Colorado Eating Disorder Program (CHCO-EDP) over 1 year of treatment/recovery, compared to a healthy, physically active control group. The specific aims include: 1) examine physical activity participation (as measured by a wearable activity monitor) and its association with compulsive exercise and eating disorder behaviors, and 2) determine changes in BMD and bone microarchitecture and estimated strength (as measured by high resolution peripheral quantitative computed tomography; HR-pQCT) and the impact of weight-bearing physical activity on these bone outcomes. The findings of this study could shift current clinical paradigms to improve the