Inclusion Criteria:  Adolescent boys with haemophilia A or haemophilia B (for experimental group) and healthy adolescent boys (for control group).  Exclusion Criteria:  To be with another congenital coagulopathy such as von Willebrand syndrome. To be unable to stand without support due to hemophilic arthropathy. To be having another musculoskeletal problem. To be developing inhibitors against factor VIII-IX. To be having plasma level of factor VIII-IX above 6%